Roll your own

It’s the height of summer, and we are enjoying a week’s vacation at the alt-QTH in New York’s beautiful Southern Tier. The weather is warm and dry, with occasional afternoon thunder showers keep everything green, and the pace is slow and peaceful. I usually bring up lots of radio projects to occupy my time, and this year was no exception.

I have always been very interested in portable QRP operation, and have been building out a couple of portable kits for that purpose. The most recent features the MTR-4B trail-friendly rig, combined with a SOTABeams 30 foot fiberglass mast, all of which fits easily in a day pack. I have long been a fan of end-fed half-wave (EFHW) antennas, and have a couple made up on 40 meters – with a small tuner these wires can be used on multiple bands. They require only one point of support, virtually no feed line, and are lightweight, good performers.

Just a couple of weeks ago, I came across a blog post by Michael, G0POT, where he describes his experience building a trapped EFHW for three bands, 20m, 30m, and 40m. This antenna can be used without a tuner on those bands, which is a hiking plus – one less piece of gear to carry.  The key to the antenna’s success is a 1:60 impedance transformer, or unun, which can be built in a small box. This becomes the rig-end termination of the antenna. Michael provides links to PA3HHO’s blog, with good pictorial instructions on how to wind this unun on a ferrite core. The resulting antenna is lightweight, needs no additional accessories, and performs well – it has become my portable favorite.

Now we come to the vacation story. I bought two toroids to make the unun, and still had the second one with me. I also have an old 1:4 balun built from a kit that I never use. Sitting on the deck looking for something to do, I decided to re-purpose the box and fittings from the balun to house a second 1:60 unun. These things just seem too useful not to have a spare on hand.

Well no problem, I brought tools and materials to build with, but unlike the primary QTH there is no well stocked bench here. And now, with the demise of the local Radio Shack store, no handy place to pick up that odd resistor you don’t happen to have.
Well, the odd resistor was in fact the issue. When I had made the first unun, I tested with my antenna analyzer and a 3.3 kOhm resistor, just to verify that I was seeing around 50 ohms (plus or minus) with the resistor across the output terminals. Just a sanity check, I’m never quite sure I’ve counted the turns correctly. I did not have the resistor with me in the kit…

Of course I could just build the thing and check it out with an EFHW attached to see how it performs, but it got me thinking. If I were stranded on a deserted island with a rig that needed a 3.3 kOhm resistor to become functional to call for help, and had only typical household items available (okay so not too deserted an island. Think abandoned resort with no Radio Shack nearby) could I fix the rig?

I asked myself the “what are resistors made of?” question. Precision metallic oxide films seemed beyond the realm of homebrew possibility, but what about good old carbon? We have lots of old crappy pencils lurking in the kitchen drawers, so I tracked one down that didn’t look too pristine, cut the eraser end off, and measured the resistance of the lead – only 16 Ohms, very low, but definitely promising.

To increase the resistance, I figured you have to reduce the cross-section of the material, so I tried making a dark pencil mark on a 3×5 index card and measured the resistance – about 10 Megohms. This could work.

My lovely XYL, Janette KC2LLA, supplied a very soft drawing pencil (more graphite, less clay in the lead), and I started systematically filling in dark lines of pencil lead on the 3×5 card, checking the resistance as I went. It continued to decrease to about 100 kOhms, then kinda stalled as I added more graphite. It occurred to me that the point of contact, (the meter leads) might be having an effect, so I added two alligator clips across the stripe, and the resistance dropped dramatically.

With the alligator clips in place, adding more graphite continued to reduce the resistance, but with less and less effect as the width of the graphite area moved out beyond the end of the alligator clips. It seemed to bottom out at around 6 kOhms – at this point Jan had a brilliant idea: cut the graphite area in two, and connect the two pieces in parallel.

Graphite covered index card pieces, ready for parallel hookup

Graphite covered index card pieces, ready for parallel hookup

I placed the two cut pieces, graphite sides facing out, between the clips and voila – 3 kOhms! By moving the position of the clips slightly I was able to dial in 3000 Ohms pretty precisely.

3k on the button!

3k on the button!

After assuring myself that the resistance reading was stable and repeatable, I proceeded to build the unun. Testing with the home-made resistor showed that the windings were fine.
The unun went in the box, and a re-check with my paper resistor showed good results.

Testing the 1:60 unun with a paper resistor!

Testing the 1:60 unun with a paper resistor!

It’s unlikely that the paper resistor will find a permanent home in my test equipment, but it was a fun and interesting experiment in kitchen physics that worked surprisingly well.

73,
de N2HTT

 

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Nice guys.

I’m very excited about operating out-of-doors this season. It seems to be in the air: the May 2017 issue of QST is featuring portable operating, with a nice assortment of hiker-ish tools adorning the cover. It wasn’t that bad a winter as winters go, but apparently we are all aching to get outside and get a little fresh air. And play radio, of course.

So for the last few weeks I have been getting together my kit to try my hand at SOTA (Summits on the Air). Basically, take a hike, climb a hill, set up a state-of-the-art QRP station, work a pile-up, pack up and go home. And, post lot’s of photos…

In addition to the physical fitness aspects of this ham radio niche (I’m working on that – actually, that’s part of my sudden fascination with hiking), there’s the challenge of setting up a station in any and all conditions. And, the toys are just the best.

I recently purchased a trail-friendly QRP rig, the MTR-4B from LNR Precision. I have only just started to use it, but I am really liking this little rig. Really essential QRP radio, nothing extra but everything you could want. I’ll probably do a write-up on it in another post, but in this post I want to discuss a critical accessory that took me a while to figure out. The fiberglass, telescoping, antenna mast.

Naturally, operating en plein air requires an antenna, and those pesky things generally need to be elevated into the air, the higher the better. There are two basic models for portable antenna supports:
“Throw a wire into a tree”
and
“The lightweight telescoping fiberglass push-up mast”

You really need to be prepared to employ either when you arrive at your summit. Of course, you may find a perfect, conveniently placed tree to throw a wire up into. (I wrote a blog post about this a while back.) Then again, you may not. Or, you may not want to, because you are in park land where you are not permitted to attach anything to the trees. In that case, the second choice is the way to go.

There are readily available, inexpensive fishing poles (called “squid poles” or “crappie poles”) that can be used to support an antenna at a reasonable height. These are typically 16 – 25 feet long when extended, but they suffer from two drawbacks: first, being intended for fishing, they are extremely flexible especially at the tip, and the weight of a wire antenna can cause the end to bend over sharply, and even break under the right (wrong) conditions. The other disadvantage is that collapsed, these things are about 4 1/2 feet long, or longer. You could pretend it was a hiking staff, but it seems just a cumbersome thing to carry on a hike up a hill.

No, what you want is a purpose-made fiberglass mast designed with hiking in mind. The one I have is from SOTABeams, extends to about 33 feet, and collapses down to about 26 inches. It weighs about three pounds, not a trivial load while hiking, but definitely worth its weight in altitude. This mast will easily support an end-fed half wave dipole (my favorite wire antenna) at a point a couple of feet from the top without bending over. Perfect… except it needs to be guyed in place.

Here’s the rub: it’s a beautiful day, you’ve hiked to the top of your local summit ready to deploy your station, but you are alone. Everyone had something better to do than take a hike to place where they could hold your mast up while you set up the guy lines. So now you are trying to somehow balance the mast against a rock or your daypack while trying to get the guy lines snug, running around in a circle over and over. It can’t be done. I know.

So it became necessary to figure out how to put up a 30 foot mast with four guy lines alone, and I think I’ve figured it out. All you need to do is a little one-time prep work before you head out, and you’ll be able to set up your mast alone in just a couple of minutes without even breaking a sweat. The answer makes use of simple trigonometry. (If simple trigonometry is not available in your area, regular trigonometry will do.)

The guy line scenario usually consists of four (but you can get away with three) guy lines attached to the mast some ways up the pole, extending out at a 45 degree angle, and anchored in the ground. The method I’m about to describe will work for any guying system, but since I purchased a guying kit with my mast from SOTABeams, I’ll describe how it works with that. My kit consisted of a guying ring (actually a plastic square with a round hole that fits around mast, plus 4 attachment holes), and a generous length of fluorescent yellow lightweight cord. You divide the cord into 4 equal parts, and tie each part into one of the attachment holes using a bowline knot. This is the starting point for my single-handed guying technique.

But first, a word about knots. This technique relies on using specific knots, and I’ll tell you what they are, but I’m not going to explain how to tie them. Look them up on Youtube, you can find much better descriptions than I could give. But do use these specific knots, it matters.

Okay here goes: the one-time preparation you need to do to your guy lines.

  1. Place the guy ring on your mast, and measure how high up from the base it rests. You can do this with no wires or lines attached by extending the mast out horizontally on the ground. This measurement is very important, so make sure the guy ring is sitting snug on the mast before you make the measurement. With my mast and setup, the ring is 10 feet 6 inches above the base of the mast.
  2. For each guy line, measure a distance equal to the height of the ring from the point where the line attaches to the ring. At this point, take a bight of the line (a bight just means fold the line and make an open loop) and tie an overhand knot, to create a permanent loop in the guy line at that point. After this step, I had a permanent loop 10 feet 6 inches from the attachment point in each of my guy lines.

    A Permanent Loop (bight tied in an overhand knot)

    A Permanent Loop (bight tied in an overhand knot)

  3. Here’s where the trigonometry comes in: each guy line when taut forms a triangle, with one point being the guying ring, one point the base of the mast, and one the point of attachment to the ground. We want the angle at the ground attachment point to be 45 degrees, and that means that the ground attachment point will be exactly as far away from the base of the mast as the guy ring is up the mast. (10 feet 6 inches in my case).
    And we can also compute the length of the guy line from the ground attachment to the guy ring, it will be 1.4 times the height of the guy ring (trigonometry) or in my case 14.85 feet.

    Detail drawing explaining trigonometry

    Detail drawing explaining trigonometry

    Do this calculation for your guy ring height, and round the answer up the next foot, because we want a little slack. I used 15 feet as my value. Measure this distance from the attachment point of the guy line, and tie another permanent loop at this point. Do this for each guy line.

So now you have 4 guy lines, each with two permanent loops tied in them at the same distances.

Guy line with two permanent loops tied in

Guy line with two permanent loops tied in

You are now ready to put up your mast alone. Here’s how to do it:

  1. Select the spot where the base of the mast will go, and stake the guy ring on the ground through each of the attachment loops. Stretch each line out straight in the direction it needs to go. For four lines, each opposite guy should line up straight.

    The Stakeout

    The Stakeout

  2. For each guy in turn, take the stake from the guy ring loop, and push it into the ground where the first permanent loop is. You don’t want to put the stake through the loop, just next to it using the loop as a location marker.

    Use the first loop to position the stake.

    Use the first loop to position the stake.

  3. For each guy, place the second permanent loop around the stake and anchor it. We’re done with the first loop.
  4. Place the mast on the spot where it will go, and start to extend it through the guy ring. Don’t forget to attach your antenna after you’ve got the mast going through the guy ring. Really.

    Starting the mast up

    Starting the mast up

  5. Extend the mast a section a time. Ignore the guy lines, pay attention to the antenna wire which is going all sorts of places you don’t want it to.

When the mast is fully extended, you can let go. The guys will be loose, but have enough tension to hold the mast upright, although leaning at an angle.

Self-standing, but leaning over

Self-standing, but leaning over

Now it’s time to adjust the guys for proper tension.

To make a tensioning mechanism we’re going to use two knots: a slip loop, and a trucker’s hitch. Go look them up, and then come back here. (Here is a nice YouTube video that demonstrates all the knots I have mentioned.)

Okay, start with guy line opposite the direction the mast is leaning. We will do this on all guys in turn, always moving next to the guy line opposite the lean.

  1. Tie a slip loop in the guy line about three or four feet up from the stake.
  2. Grab the line, and slip the permanent loop off the anchor. (Don’t let go of the line.) Loop the standing part of the line around the stake so it can move freely, and pull it up so there is a little tension on the line.
    Pull the free end of the guy line through the slip loop, and pull it to tension it the way you want. Tie a trucker’s hitch around both parts of the line to secure it.

    Guy line tensioned and secured with trucker's hitch

    Guy line tensioned and secured with trucker’s hitch

Voila, a beautiful, self-standing mast you put up all by yourself. You can tweak the tension on the guy lines until the mast is perfectly vertical. Now what was it I was going to do with this mast… oh, yes..

Beautifuly guyed mast, which we needed for some reason..

Beautifuly guyed mast, which we needed for some reason..

I know this guying process sounds a little complex, but believe me after you have done it fifty or sixty times it will become second nature. And speaking of nature, what could be better than enjoying the outdoors and ham radio at the same time, hanging around with a bunch of nice guys.
73, de
N2HTT

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A cootie?

Settling in for the long winter season, I have lots of bench projects waiting in the queue. Some have time constraints and are higher priority, such as getting my HX-1681 back on the air in time for this years Novice Rig Round-up (0000 UTC on FEB 18 through 2359 UTC on FEB 26, 2017). Others, like finishing the one tube regen I started, or repairing half a dozen broken items, will rise to the top of the list in due time. And there are some new home brew ideas I am eager to start, definitely including another QRP tube transmitter this year.
So with all these worthy items awaiting attention, how do I spend the little bench time I had available over the last two weeks? I built a cootie key, of course.

The "Depot" cootie key

The “Depot” cootie key

A cootie key, or sideswiper as they are also called, is a key that is operated with a horizontal motion of the hand, rather than the up-and-down motion of a straight key. It has two contacts, left and right, and unlike a paddle a key closure on either side closes the same circuit. Cooties go way back; they were the first attempt to solve the problem of “glass arm” (what we call a repetitive strain injury today) which was the frequent result of too much straight key activity. It is said that the first cooties were made by enterprising telegraphers who mounted two straight keys base to base on their sides, with the keys wired in parallel. Later, commercially made cooties appeared, touting less fatigue and faster keying speed as advantages.

In the early 20th Century the “bug” or semi-automatic key made its commercial debut. Since that key automatically completes the dits, the telegrapher does less work, and soon the bug pretty much completely supplanted the cootie key and they more-or-less disappeared. Today the advent of inexpensive electronic keyers and the paddle, which uses two separate circuits for the dot and dash, have pretty much relegated bugs and cooties to the attic, to be used only by aficionados of retro and antique gear.

But there is one other group of hams who have traditionally embraced the cootie: those seeking a key for next to no cash outlay. Cooties can be made out of any piece of springy steel and two contact points. Hacksaw blades are commonly used, but I have seen pictures of cooties made from steak knives jammed point first into a block of wood! This is a technology that lends itself to improvisation, and that is what ham radio is all about.

Sending with a cootie, or side-swiping, is tricky business. Basically, you start each character on the same side of the key (I’m right-handed, I start with my right index finger first), and then alternate thumb and finger creating the elements of the character. The timing is all on you, much as it is with a straight key. I found the technique difficult at first, but with some practice still find it difficult. My inclination is to start each character with whatever finger was left over after completing the last, but I can see that method quickly leads to disorganization and madness. The always-start-on-the-same-side approach makes sense if you think about each character as a separate unit, always formed the same way. Harder to learn, but I think you get a better sounding result.

I have actually owned a very fancy cootie key for some time now, made by Llaves Telegraphicas Artesanas (LTA) in Spain. The gentleman who made these keys, Guillermo Janer, EA6YG, has been a silent key since 2008, but you can still see a very nice page describing the keys he made at Morse Express.

LTA cootie, on a nice chunk of granit countertop

LTA cootie, on a nice chunk of granite countertop

This key is beautifully crafted, but really awkward to use. With the pivot in the center the throw is short, and the stiff brass arm has no give upon making contact, making for a very jerky feel when keying. After several tries to get used to it, I gave up and it sits very handsomely on the shelf where I display my key collection.

I got interested in cooties again when just recently one came up for sale on a club swapmeet listing. This was a cootie made by Vizkey. It gets excellent reviews, and I got intrigued. The Vizkey version is based on the venerable hacksaw blade which simultaneously provides the contacts and the spring tension for the key. These keys are a bit pricey though, and I wondered if there was a way to experiment with cooties that would require less commitment.

On to steak knives and blocks of wood.. I researched inexpensive home brew options, and came up with this really nice design by Mike Maynard, KC4ICY. His Depot Key, so named because all the parts can be obtained from, well, you know. Anyway it looked like a nice inexpensive way to play with a cootie, and being based on a hacksaw blade I figured it would be pretty much the authentic side-swiping experience. Mike estimates that his version of the cootie can be built for about $10. I think the actual number is closer to $20, but I didn’t have any old hacksaw blades handy and the Depot only had packages of two available. I did have most of the rest of the hardware on hand, as well as the wooden base (leftover from the external VXO project) and the wood finishing supplies (leftover from the Bayou Jumper.) I bought the angle irons, the hacksaw blade, and the 1/8 stereo plug which I was out of at the moment. And the buttons for the finger pieces.

My first attempt at finger pieces was to cut out two rectangles from a heavy polyethylene container. They looked awful, so I went searching through the craft department of our local Wal-Mart, and found a package of six really cheap coat buttons for $2. The buttons had flat backs so they fit together nicely around the hacksaw blade, and a #6 bolt fit the hole perfectly.

Coat button finger pieces

Coat button finger pieces

Construction was very straightforward. I cut the hacksaw blade to length using a pair of tin snips (don’t forget the safety goggles when working with springy steel), and drilled a hole near the cut end to accommodate the fingerpiece attachment. The blade was a little tough to drill, but no big deal really, just go slow and perhaps use a drop of oil on the bit. I used a wire brush in my Dremel tool to remove the paint from the hacksaw blade, as it was a rather garish white and yellow color scheme.

In a departure from Mike’s design, I added a bolt across the top of the angles holding the contacts, so I would only have to wire one side. This eliminates the possibility of using the key as a single lever paddle, but adds some rigidity to the contact posts.

Strain relief

Strain relief

The only other feature I added was a staple and a dab of hot glue to act as a strain relief for the cable, which is a short length of RG-174 coax. I put a piece of non-skid foam backing, (the kind used under rugs) on the underside, held in place with a few pieces of double-sided scotch tape. Although key is very light, this arrangement holds it in place just fine, and there is no need to hold the key with your other hand while keying.

Non-slip rug backing

Non-slip rug backing

So how does it play? Not bad, actually. The springiness of the blade, and the soft landing with a little give on the contacts is very pleasant. It makes a little noise when keying, but not nearly as bad as the LTA key, which clanks dramatically with each stroke.

I’ve been practicing off the air with it, and while I like the feel and the side-to-side keying, I still sound pretty awful. There is a tendency to run the dits together, and shorten the dahs. Based on internet advice, I set the contacts pretty far apart – this is supposed to help avoid the running together.

There are many online resources for on the art of sideswipery – the SideSiperNet website lists nets and other information, and has a gallery of keys posted by cootie afficianados that is very interesting to browse through. You can also find a short essay on the practice of side-swiping at Morse Express. The also feature another commercial cootie, the GHD-501 (see the bottom of the page), a pricey but beautiful instrument.

I like my homely little cootie, and will continue to play with it – maybe even venture out onto the air someday if my sending with it ever becomes comprehensible. I did get to satisfy my side-swiping itch without investing in an expensive instrument – dodged the bullet on that one.

73,
de N2HTT

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Another radio, another VXO

Well, another holiday season has steamrolled past, and as usual the need to celebrate rose to the top of the charts once again. My lovely XYL is always on the lookout for a ham radio themed holiday present for me, God bless her, and this year I was able to suggest something without the usual churning to find a suitable idea. Starting back in November, I became aware that the Four State QRP Group (4SQRP), renown for their excellent kit projects, was about to introduce a new QRP set paying homage to the paraset spy radios of World War II. I haven’t built a kit in a while, but as soon as I heard of this one, I was instantly lit up. What a cool idea: a little QRP transmitter, and regen receiver, made to fit in a wooden box harking back to the suitcase sets that went behind the lines in WW II. They had me at “wooden box”.

The Bayou Jumper, a Paraset replica in a wooden box.

The Bayou Jumper, a Paraset replica in a wooden box.

Of course this modern paraset replica uses a very different implementation of the technologies incorporated in the 1940s version. Although both the historical parasets, and the 4SQRP unit (called the Bayou Jumper) make use of a regen receiver, the modern rig implements the receiver using FETs and varactors, where the historical rig was all tubes.
The transmitter in the set is basically the 4SQRP NS-40 transmitter sharing a single circuit board with the regen. The NS-40 was another 4SQRP club kit, a simple but very robust 40 meter transmitter, using a 2N7000 oscillator driving an IRF510 FET PA. It produces a healthy 5 watts, and features an unusual low pass filter implemented with spiral coils built into the circuit board, thus eliminating the need to wind two additional toroids.

Bayou Jumper board, spiral coils visible upper right.

Bayou Jumper board, spiral coils visible upper right.

There is a wealth of information about both the Bayou Jumper kit, and the historical sets available on the kit website. There is also a Yahoo discussion group, with a lot of building resources and hints, and links to some historical documentation of the parasets of yore. Take a look at the files section of the Yahoo group for some good sources of historical info about the parasets. At the time of this writing, the first run of 100 kits is sold out, but they are rekitting them for a second run immediately, so keep an eye on the website if you are interested.

While perusing the historical info, I learned that the original suitcase sets were designed to be “portable” and weighed 42 pounds. By the end of the war a few years later, that weight had dropped to 9 pounds! And of course the replica weighs much less than a single pound, including the wooden box.

So I first heard about the BayouJumper right at the end of the November, and immediately checked the website for availability. “Coming soon” was the intel at the time, but unlike other kit radios, this one had a built-in parallel project: the wooden box. The radio is designed to fit a specific hinged wooden box available from HobbyLobby. If you are lucky enough to live near a HobbyLobby retail store, you can purchase just the box that fits the radio, ordering online you have to buy the set of three, which leaves open the possibility of other wooden packaged projects. Of course, the woodworkers among us could home-brew something fancier (and have, check the photo section of the Bayou Jumper Yahoo Group), but for me the prospect of obtaining the box, and decorating it provided a pleasant diversion while waiting for the kit to become available.

The Yahoo Group provided a wealth of advice on how to finish the box, which I took literally. I sealed my box with several coats of Minwax Polycrylic finish, and then used their Polyshades stains over the clear coat. I went through a number of colors I didn’t like, and wound up with a light coat of “Mission Oak”, with a heavier coat of “Honey Pine” over it. All I can say is that the samples at the hardware store look nothing at all like the color I got. Mine turned out looking like a pine box with a layer of travel grime over it. I’m not complaining.

Wooden box with travel decals

Wooden box with travel decals

Pictures of the project prototype showed it plastered with vintage travel stickers, miniaturized to fit the scale of the box. These turn out to be home-brew decals! A very interesting, and potentially useful technology. You purchase you sticker images in the form of downloadable PDF or JPG files (I got mine on etsy), and print them on special decal paper, which is available not surprisingly from decalpapers.com. After printing your images using high-quality photo settings for the printer, you spray the pages with several coats of gloss plastic finish like Krylon. After they are thoroughly dried, cut them out, soak briefly in cold water, and slide into place on the object to be decorated. Couldn’t be easier, and it actually worked. I finished with a light coat Polycrylic to lock them in place.

Decorated box (romance side.)

Decorated box (romance side.)

With the box all prepared, and with more time to wait until the kit shipped, I starting thinking about how to accessorize my as yet unbuilt paraset. Shipping along with the kit are these neat little boards that allow you to solder on a modern HC49/U crystal, and attach two pieces of #10 solid wire to make a board that will plug into a crystal socket intended for an FT-243 crystal.

Both sides of HC49 to FT-243 crystal adapter board.

Both sides of HC49 to FT-243 crystal adapter board.

Photos of these little boards on the Yahoo group showed a variation with pads for a trimmer capacitor and an inductor in series, to make a pluggable, pullable crystal. With my recent fascination with VXOs and crystal pulling still running high (see last post), I got the idea to build a pluggable VXO for the SKCC frequency of 7.055, using a bunch of shorty HC49 crystals, an inductor and a polyvaricon cap. I used a piece of single sided PCB, and just isolated the pads with a Dremel tool by hand. The circuit is very simple: just the variable cap and the inductor in series with the crystal. I used five crystals in parallel – putting them in parallel makes them easier to “pull” and increases the frequency range you can get. Also those little shorty crystals don’t have a lot of quartz in them, paralleling them increases the current they can handle.

My finished VXO used a 10 uH choke I had lying around, a 200 pF polyvaricon, and gives a range of about 3.5 kHz. Just enough to dial in that guy calling CQ almost but not quite on your frequency. I’ve used it with the W1TS simple transmitter with very good results.

7055ish pluggable VXO

7055ish pluggable VXO

Finally it was just a matter of watching the website for the release of the kit, hoping it would be in time for a Christmas delivery. By dint of checking my phone every 30 seconds for 10 straight days, I was aware of the kit release pretty promptly on the first day, Dec 18. I ordered pronto, and by Thursday before Christmas, had my kit in hand to be wrapped and placed under the tree. The minor obsession with early ordering turned out to be worthwhile – the first kit run of 100 was sold out in five days. Fear not, 4SQRP is doing addition kitting runs, and the kits will be available again soon. Watch the site.

Santa came through, and since I wanted to use the radio from the alt-qth later in the holiday week, I needed to get started on the build right away. The kit is straightforward to build, and the documentation is very good. There were a few minor inconsistencies, but checking the Yahoo Group resources before building should alert the builder to any gotchas. I am a slow kit builder: I check the value of each part with a meter, and mark up both the parts list and the schematic as I progress. It took me 5 hours over two sessions to complete the build, but I imagine a faster worker would take much less time.

Everything worked at first power up… but some major tweaking was needed. The transmitter section was fine, working as advertised and putting out a solid 5+ watts into a dummy load. The regen was going into and out of oscillation with the regen control, but I could not find the oscillator signal at all using my KX3. After reading on the reflector that it could be quite a ways above 7.3 MHz, I tried again, and finally found it up at 7.752!

Jim N5IB, one of the designers of the kit has been offering guidance on the reflector, and indicated that moving the regen down into the ham band was accomplished by either using the trim cap, or squeezing the turns together on the toroid. I wasn’t having any luck with the trim cap, which is only a 20 pF adjustment, so I took a look at the toroid on a photo of a completed board on the Yahoo group. Big difference, so I squeezed the coils to make them look like the photo, and that did the trick.

Toroid before squeezing

Toroid before squeezing

Toroid after squeezing

Toroid after squeezing

I wound up with a tuning range of 7.030 – 7.175 which is kinda high, but covers all the areas I am interested in. While I was testing with everything opened up, it was going from 7.015 up, but it seems to have jumped up once everything was in the box. Jim provided a hint on moving the range down a bit – adding a few pF across the base of the trimmer cap, and I may revisit this as some point. But for now it is working fine and I decided not to mess with it further. I painted the coil with some home-brew coil dope (artisanal) since I wasn’t able to get my hands on any clear nail polish.

Artisanal Coil Dope

Artisanal Coil Dope

My regen goes in and out of oscillation at about 75% of the pot range, and I wasn’t able to budge it with the corresponding trimmer cap. Anyway, I can get it to go into and out of oscillation at both ends of the tuning range, that’s all it needs to do, so again I decided it was good enough.

While hunting for the tuning limits, I was turning the rig on and off by plugging and unplugging the power cord, and I broke one of the tabs on the power jack. It had been mentioned on the Yahoo group that they are fragile and not to bend them too much on installation. Luckily, it was the ground side that broke, and I was able to solder the wire directly to the ground side of the jack. That was the worst mishap I encountered with the build, everything else went smoothly.

Well one week after Christmas is famously Straight Key Night (oh yes, also Hogmanay) and what better time to try out my new Bayou Jumper on the air. I have collected a fair number of crystals over the years, and so have lots of frequency options available on 40 meters. Because of SKN, the CW portion of the band was happening, leading to a textbook example of:

N2HTT’s Axiom of Operating Rock-bound

For any given crystal frequency there will be either:

  • A. Someone calling CQ exactly 500 Hz above or below you transmitter frequency with his passband cranked down tight, or:

  • B. Someone exactly on your crystal frequency, in hour two of a four-hour rag chew.

The upper end of 40 meters was too busy to shoe-horn in, but luckily I have a few rocks up in the old Novice CW portion of 40 meters, above 7.100 MHz. The Bayou Jumper is shipped with a 7.122 crystal (apparently the QRP-ARCI frequency) so that’s a good spot to look for them. I finally chanced across Tommy, AA4TB, calling CQ spot on 7.1175, one of my rocks. He was also QRP, running an HW-9, and we had a short but pleasant contact although he was faint and there was lots of QRM on my side. He must have been mystified when I told him my rig was a Bayou Jumper, and I was so excited that I forgot to send my SKCC number, but all in all, an excellent first QSO. A while later I worked Bill, KB0BWY on the same frequency, for my second and final SKN contact this year. The QSO with Bill is the current standing distance record for my Bayou Jumper at 1400 km.

On the air for SKN!

On the air for SKN!

Aside from breaking in the Bayou Jumper, SKN was kind of a bust for me this year as suddenly, on Friday afternoon (Dec 30th) I completely lost the ability to be heard on the air. I usually check for my signal on Reverse Beacon Network, but at some point Friday I just disappeared. I tried different rigs, actually put up a new antenna (40 meter sloper dipole), went QRO, switched coax, but all to no avail. I wasn’t getting out. It wasn’t until Sunday afternoon that I took the MFJ tuner out of the circuit, and just as suddenly I was back! Something must have fried in the tuner; I have it on the bench but haven’t had time to check it out yet. Unfortunately it was the last item I switched out, so I was down for most of the event.

After playing with the Bayou Jumper for a few days, I’m beginning to understand how the hams of yore could operate successfully using simple regen receivers. I’ve built a couple of regens, which work great, but I just couldn’t figure out the interplay between transmitter and receiver. Regens are so sensitive, they get blown away by the local signal when you transmit. Forget about hearing yourself in the receiver as a sidetone, or spotting you transmit frequency.

The Bayou Jumper revealed the secret to me: when you are transmitting, turn the receive audio OFF. Works like a charm, just mute the darn thing. No need to spot your transmitter, just get the receiver in the neighborhood of where you are calling, and sweep up and down a few kHz looking for a reply. It couldn’t be easier. I was definitely over thinking the whole process. I am going to try my old regens out with one of my home-brew transmitters, to see if I can get this to work.

Oh yes, one other thing: the Bayou Jumper has no sidetone. Actually not a big deal, your sending will be fine even without one. Where we’re going, we don’t need sidetones…

73 (and Happy New Year)
de N2HTT

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Wiggle room.

I’ve been spending a lot of time messing with VFOs recently, both vintage tube units and modern digital synthesis projects, all driven by the quest for frequency agility with homebrew QRP rigs. My favorite homebrew transmitter is the 2-tube W1TS rig, which has stubbornly resisted cooperating with an outboard VFO. Even Ralph WB8DQT, the author of the project, states in his documentation that VFO operation was not a design goal for this lovely little transmitter. I wholly agree; I have tried with a number of VFOs and a few different interfacing techniques, and I haven’t been able to get sufficient drive from an external VFO. The thing is just much happier with a crystal in its socket.

A while back, I had a thought: why couldn’t you add the parts necessary to create a VXO circuit around the crystal, and plug that VXO circuit into the crystal socket? You’d get some variability with a crystal driving the 6C4 oscillator. It should work, right? I tried putting together such a circuit, which never did work, since I didn’t have any clue what I was doing. It went on the pile of unsuccessful experiments, and I forgot about it.

Then just recently, I discovered acorn tubes. These tiny little tubes were popular in the 1940’s in VHF applications. Their small size resulted in less inter-electrode capacitance, extending their useful frequency range into the VHF. You can find them around on eBay, and from some of the sellers of NOS tubes.

I got interested when I came across a couple of articles by Dave Ingram K4TWJ (sk) in CQ Magazine describing QRP transmitter projects using these little tubes. I tracked down a bunch of his acorn circuits (old CQ magazine content is available behind a pay-wall here), and started accumulating parts to build a 2-watter using two 955 acorn triodes in a push-pull configuration. I have almost all the parts for this project and am looking forward to starting it soon. So what does this have to do with VXOs?

One of the acorn tube articles described an optional VXO circuit that could be substituted for the crystal in the oscillator. This got me thinking about my failed outboard VXO attempt, and I did a search for VXOs for use with tube rigs. I found a number of circuits: although mostly intended for use with solid state QRP rigs, there was one result that hit the jackpot.  I found a page showing a number of external VXOs intended to drive tube rigs done by NT9K,  Bill. (Scroll down this page to find the VXOs. Bill has a very interesting website, well worth looking around while you are there.)
This was exactly what I had tried building on my own a while back, but apparently his circuit worked!

I reached out to Bill and he replied to my email promptly, with the information I needed to try to reproduce the VXO. As is turns out, the original inspiration for the circuit was Dave Ingram again, who described it in another of his CQ columns. Bill provided the critical missing information – how much inductance was needed – and I built one of my own.

External VXO with HC/6 crystal onboard

External VXO with HC/6 crystal onboard

I actually had most of the parts on hand, except for the 365 pF air variable capacitor. These can be bought new from Antique Radio Supply fairly reasonably, and they are nicely made units. ARS ships really quickly too, so I had everything I needed in fairly short order.

Construction is point-to-point and the circuit is simple: the variable cap and inductance are placed in series with the crystal, with a short cable to allow plugging the circuit into the crystal socket on the rig. Using Bill’s projects as inspiration, I mounted my circuit on a small wooden plaque obtained from the local craft store. All the hardware is stainless steel and brass. Two posts allow easy interchange of the inductor in the circuit, which is actually quite handy as I tried a couple of different ones before settling on 40 turns wound on a T-68-2 powdered iron core, about 10 uH.

I had the ceramic FT-243 socket on hand and used that because most of my crystals are either vintage FT-243’s, or modern HC/49 style crystals mounted inside vintage FT-241 or FT-243 holders emptied of their out-of-band crystals.

Many VXO circuits are designed to use more than one crystal, all on the same frequency. It is easier to get more of a frequency swing with multiple crystals. But I am only looking for 1 or 2 kHz around the crystal frequency, just enough to work those guys you hear 500 Hz off your rock, running tight passband filtering, who will never hear your call. For that reason, and the fact that I don’t have duplicates of any of my FT-243 rocks, I opted for a single crystal socket. It would be easy enough to add another socket in the future if this gizmo proves useful.

I enjoyed the Thanksgiving weekend at the alt-QTH this year, as we entertained the entire family for Thanksgiving dinner. During the quiet moments, I worked on this little VXO project, and by Friday evening it was ready to try out. The W1TS transmitter lives at the primary QTH, so testing would have to be done with my Knight T-60 transmitter which is currently set up in the shack. I tried a number of different crystals and a couple of inductors, and got a range of results.

VXO connected to the Knight T-60 Transmitter

VXO connected to the Knight T-60 Transmitter

The two inductors I tried were hand wound: one was 5 turns of 22 ga wire on an FT-43-50 ferrite core, and the other was 40 turns of the same wire on a T-68-2 iron powder core. The ferrite version measured 13 uH on my digital LC meter – I didn’t measure the other one but the calculated value should be about 10 uH. In testing these coils performed about the same, I went with the red type 2 core, I think it looks nicer.

Results varied a lot with the type and activity of the crystal. Some of my vintage FT-243 rocks only moved a rather disappointing 700 Hz, but the smaller HC/6 types gave much better results with the same setup, swinging about 3.5 kHz. The HC/6 style rocks are the ones in the metal can, with the same pin spacing as the familiar FT-243s. I am looking forward to try this setup with the modern HC/49 crystals mounted in FT-243 holders that I use with the W1TS transmitter. I have a feeling that these will swing pretty well, as they are very active compared to the old vintage rocks.

HC/6. FT-243, and FT-241 crystals all share same pinout

HC/6. FT-243, and FT-241 crystals all share same pinout

Connection to the rig is with a jumper cable that can be plugged into the rig’s crystal socket. I had a plastic plug on hand that fits the FT-243 socket (left over from an RF pre-amplifier project), and I used a short length of 300 ohm twin-lead for the jumper. This has much less capacitive loading than coax, but a short length of coax would have worked fine as well.

300 ohm twin-lead terminated with weird plastic plug

300 ohm twin-lead terminated with weird plastic plug

Another plug idea that I have used often is to open up and empty a vintage FT-241 crystal holder (these were mostly used for VHF radios, and are plentiful at frequencies outside the ham bands), drill a hole to accommodate the coax, and use the holder as a plug for the crystal socket. You can do this with an Ft-243 crystal as well, but I think the larger size of the FT-241’s make them easier to use for this purpose.

Coax terminated with plug made from an FT-241 crystal holder

Coax terminated with plug made from an FT-241 crystal holder

So Thanksgiving this year was great: warm house, big family dinner, snowy landscape (yes, we actually had a foot of snow the Tuesday before), and a small homebrew project. Much to be thankful for.

73
de N2HTT

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Novices.

Lately, I have been completely preoccupied with the completion of my Novice station at the alt-qth (Otego, NY). It all started with participation in a vintage rig event last February, the Novice Rig Roundup. Since then I have been obsessing a bit about creating a fully functional Novice station, first by experimenting with refurbishing a transmitter/VFO pair, then the Heathkit HX-1681/HR-1680 twins.

Well, the Novice station is now complete and on the air, and later in this post I will describe the additional gear I added to complete it. But before getting to that, let’s consider the history of the Novice license that gave rise to this niche. It is a fascinating history, and actually before learning about it, I wasn’t even aware that the Heathkit gear was a Novice station. Here follows a much abridged history of the Novice license:

(The following information is drawn largely from a Wikipedia article here, but also from this page, and this page.)

Starting with the Radio Act of 1912 amateurs in the US were required to obtain a license. At the outset, there was basically only one license (well, two actually, but the conveyed the same privileges, just different method of application) and all licensees had the same privileges. This license was known as Amateur First Grade in 1912, then became Amateur Class in 1927, then Amateur First Class in 1932.

The alternate license in 1912, Amateur Second Grade, allowed applicants who could not get to a Department of Commerce field office to attest to their operating qualifications, and then later be examined by a licensed amateur to become First Grade. This license was renamed Temporary Amateur in 1927. In all cases though, the privileges granted were the same, not a novice in sight.

In 1933, the licensing scheme was reorganized by the Federal Radio Commission to comprise Class A, B, and C licenses. Here the first notion of class privilege arrived.

Class A licenses got the whole enchilada, and the Amateur First Class licenses were grandfathered into this group.

Class B licensees were excluded from certain “reserved radio-telephone bands”.

The Class C license roughly corresponded to the old Second Class licenses, with exams performed by other licensed amateurs rather than at a field office, but the existing Second Class licenses were not grandfathered in and had to re-apply because the examination had been made more stringent.

The Communications Act of 1934 created the Federal Communications Commission, the FCC we know and love today which replaced the FRC. No change in amateur licensing accompanied this event.

It wasn’t until 1951 (a year particularly important to me) that the FCC restructured amateur licensing to create six license classes, including the first Novice license. The new Novice license was restricted to CW only portions of the 80, 40, and 15 meter bands (but also phone and CW on 2 meter band), with input power restricted to 75 watts. (Power restrictions were specified in terms of input power, as this was easier to measure than output power or effective radiated power. The net result was that Novice transmitters with typical efficiencies of 30 – 50% would put out a maximum signal of around 40 watts.)

The Novice license was a one-year, non-renewable affair, it was upgrade to General or out at the end of the year. In addition, Novice transmitters were required to be crystal controlled, restricting operation to one fixed frequency at a time. This gave rise to an operating style where one would call on the crystal frequency, and then listen up and down the band for a reply on someone else’s crystal frequency, resulting in a full-duplex QSO. All kinds of quaint calling conventions arose to indicate “listening up” or “down 5kc”. I am not up to speed on these, having heard of them but never used them.

Post-war surplus crystals in the ham bands were relatively plentiful but considered a big expense for a ham just starting out (usually a teenager with a paper-route budget) giving rise to all sorts of clever techniques for moving the frequencies around a bit. Crystal munging was definitely part of Novice culture.

In 1964, the FCC and the ARRL came up with Incentive Licensing, which removed some privilege from existing licensees as an incentive to upgrade. This really annoyed a lot of hams, some of which left the hobby rather than upgrade. The term of the Novice License was extended to two years in 1967, and they lost their 2 meter privileges.

In 1977 the power restrictions in the Novice sub-bands were changed when all license classes were granted a maximum of 250 watt output in these bands, and the crystal controlled requirement was removed. (This change is what qualifies my Heathkit gear as a Novice rig.) In 1978, the Novice license was made renewable with a five-year term.

As of 2000, no new Novice licenses can be issued, but existing Novice licenses can continue to be renewed. I couldn’t find a precise number, but somewhere around 1% of licensed amateurs continue to hold Novice licenses today.

So the 1951 Novice license is the model for the Novice nostalgia genre, with restricted power and crystal controlled transmitters. I’ve tried this kind of operation, and can tell you that it isn’t easy – I have a lot of respect for any op that learned the ropes this way. Thus my intense interest in a vintage station with the frequency agility afforded by a VFO, and how I wound up with my 1977-street legal Novice rig.

Complete Heathkit Novice Station

Complete Heathkit Novice Station

Centering around the HX-1681/HR-1680 transmitter-receiver twins, I have been building out my station with carefully selected vintage acquisitions, to make a state-of-the-art 1980’s Novice station. Most recently, I have added three pieces of gear.

HS-1661 Speaker

HS-1661 Speaker

The first is a Heathkit HS-1661 desktop speaker. This unit was made to match the HX/HR twins, and puts out booming audio connected to the HR-1680. Ironically, this is the third HS-1661 I have owned; one I gave to a good friend to use with his HW-16, and the other I sold as part of the package when I sold my HW-16 station. These are really nice speakers – about 5×7 inch oval in a nice metal cabinet, with an impedance of about 4 ohms. They clean up nicely, and are impossible to kill, making them a good bet when one comes up at auction or in the classifieds.

HM-2140 Watt Meter

HM-2140 Watt Meter

The second piece of gear is a Heathkit HM-2140 dual watt-meter. The one I found was in pristine condition, and is working perfectly, not even needing recalibration. They show forward and reflected power (or SWR) on two meter faces, and if you are a SSB op, can read in peak power as well with the addition of a 9v battery.

Finally, I decided to add a manual antenna tuner. If you read my last post, you know that I had intended to use an auto tuner with the station, but at the last moment I decided that would just be too anachronistic. I looked at the various Heathkit tuners that were common in the time period: the SA-2040 and SA-2060, but did not find anything that filled the bill. These tuners are all physically large and apparently very robust, and I don’t think people part with them. Those who do seem to want prices that do not seem reasonable to me, so I broadened my search.

I was delighted to come across a Cubic Communications ST-3B tuner. I had never heard of this tuner (or company) before, but apparently they were around in the 1980’s and contemporaneous with my Heathkit gear, The reviews I found of this unit were all very enthusiastic. From some additional research, it appears that Cubic Communications made mostly commercial gear, and not much ham stuff, and are still around and kicking today having nothing to do with amateur radio.

Cubic Communications ST-3B tuner

Cubic Communications ST-3B tuner

The unit I found was dirty and scuffed on the outside, but pristine on the inside, and clearly built like a tank. Some work with a Mr. Clear Magic Eraser, and using an ultrasonic cleaner on the knobs, resulted in a very presentable exterior. I will probably paint the cabinet at some point, but it’s fine as is for now. It has two charming features: the capacitors are driven by 6:1 reduction drive verniers, and if you apply 12 vdc, the meters illuminate. With the little red cube logos in each meter, the dials look like illuminated eyes, kinda cute in a spooky way. It really does load up the end fed half wave that I usually use very well.

Spooky, but cute

Spooky, but cute

This weekend saw the running of the SKCC Weekend Sprintathon, one of my very favorite operating events, and marked the maiden voyage of my new vintage Heathkit station. I was delighted to discover that I could crank the drive level way down and operate the transmitter stably at 5 watts out, thus combining all of my ham radio favorites: CW, QRP operation, and radios that glow (at least partially) in the dark.

It doesn’t get much better than that.

73,
de N2HTT

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Together Again (for the first time)

Summer is winding down, and a lovely summer it was. I think the weather here in the Northeast was the best I can remember for quite some time. Sure, we had some beastly hot, humid days, but on the whole it was great. A time to play outside, spend time with friends and family, and travel. Not so good for hanging around in a dark basement workshop, building radio gear.

Coming into the summer I had been working on a low voltage regen receiver, still a work in progress, and refurbishing the Knight V-44 VFO. The VFO needed lots of work, especially after I destroyed the main tuning coil with the careless application of an electric know (still slapping my forehead over that one.) At the beginning of June I got the coil rebuilt correctly, but was still not happy with the output into the Knight T-60. A friend of mine with access to a spectrum analyzer was going to help me out, but we didn’t get together then, and this became another project waiting for renewed attention.

But the summer was not without some ham radio excitement. The real attention-getter crept up on me unexpectedly. First, some back story:

About five years ago I discovered that Heathkit had manufactured kits in the late seventies for a CW transmitter/receiver pair. The receiver was released first, in 1978. All solid state, ham bands only with a switchable narrow filter, LSB/USB/CW, and built-in dial calibration. This was the HR-1680, and it was quite popular from the outset.

About two years later, the matching transmitter, the HX-1681 came out. CW only, no WARC bands, the transmitter was a hybrid – mostly solid state but with a tube final consisting of a pair of 6146’s that produced a full 100 watts out on 80 – 10 meters. Both units were housed in handsome matching heavy aluminium cases (Heathkit teal, of course) and both sported meters and main tuning dials that glowed red when illuminated. By slaving the receiver to the transmitter, smooth full break-in QSK was possible along with receiver muting and a sidetone. When I first heard of this pair, and researched them a bit I knew I had to have a set as my primary vintage rigs.

New arrival in the shack

New arrival in the shack

While the receivers are relatively plentiful in the used market, the transmitters are hard to come by. Perhaps because of the delay in producing the kit, or maybe the CW-only capability, but it is my understanding that the transmitter did not sell well. They are hard to find used. Soon after buying the receiver, I located an auction for a 1681 but had to let it pass for financial reasons. On and off over the last five years I would see one of those transmitters come up on auction or in classifieds, but it was never the right time. Too expensive, or the seller was selling them as a pair and wouldn’t break up the station. It never quite worked out – until this Forth of July.

Maybe it was because most folks have more interesting things to do than watching eBay auctions on a big holiday weekend, or maybe the way the listing was worded it didn’t come up on the radar, but during the week leading up to the 4th I found an HX-1681 up for auction at a an extremely attractive price. Cosmetically a 9, and completely untested by the seller who did not have the required big iron power supply. I got the nod from management, and went for it. I won the auction at a very good price, and a week later my beautiful transmitter arrived.

Becoming a new owner of an HX-1681 brings new responsibilities. I also did not have the required big iron power supply, and that became the next imperative. The power supply is the Heathkit HP-23, later renamed the PS-23 after Honeywell threatened Heathkit with litigation over the HP mark. Several versions of this supply were made: the HP-23, then PS-23, PS-23A, PS-23B and finally PS-23C. There were minor user interface changes between the models, but basically they all supplied 12 vac for filaments, two plate voltages of 800 and 250 vdc, a negative bias voltage of -130 vdc, chassis ground and a switch line to allow the rig to turn the power supply on and off. These power supplies would work with all of the Heathkit tube rigs, requiring only minor tweaking to match any of the rigs.

One used to see these things by the dozens on eBay and on the classifieds, and could usually find them for well under $100, but recently they have become more scarce, and correspondingly more expensive. I shopped around for as long as I could, but the urge to be able to turn on my new transmitter was strong, and I wound up buying one for a little more than I normally would have, had I shopped longer. It was a clear win of instant gratification over common sense. Life is short, eat dessert first.

The unit I picked was a PS-23, one of the oldest and simplest models. Later models sport a switch for changing the low plate voltage between 250 and 275 volts. On this model it’s a hardwired change, which seemed to me an advantage – since I only needed the higher voltage, a convenient front panel switch that let you set the wrong voltage didn’t seem that necessary.

The wiring looked good

The wiring looked good

The unit I selected was not the cheapest around, but the photos showed that it had been recapped with modern plastic and aluminium electrolytic caps. Since the recap kits run about $60, I figured that was one additional expense I could avoid up front. The only real downside was the unit came with a home-made, dodgy looking connecting cable, instead of the usual 8-wire covered cable. Hey, the seller said it worked, what could go wrong?

Dodgy home-made cable

Dodgy home-made cable

Okay, so the first thing I planned to do, before applying power to the 1681, was to go through the final resistance checks listed in the assembly manual. The manual itself was a bit of a challenge. Several years ago, it was common to find scans of Heathkit manuals online, but at some point someone acquired the intellectual property rights to the manuals, and began assiduously getting them off the web. Today it is difficult to find much more than schematics, and partial manuals online.

My 1681 did not come with a manual; all I had was a fragment of the assembly manual that described the resistance and initial voltage checks, alignment and adjustments, and basic operating instructions. Okay, that should be enough to get me going… until I realized that the resistance checks all referred to pictorials to locate test points, and I didn’t have the pictures. I needed to find a manual.

There are folks who sell paper facsimile manuals for specific Heathkit gear, and I was starting to look at those offerings, when I stumbled across an auction listing for someone selling a box full of unused Heathkit manuals. The assortment happened to include both the 1680 and 1681, with all diagrams and schematics, as well as manuals for some other toothsome Heathkit gear I don’t own (yet), all for a the price of a single facsimile. I couldn’t pass it up, and within a few days I had the manuals I needed along with the beginnings of a fine Heathkit library.

Lucky manual find

Lucky manual find

With the manual and pictures in hand, I opened up the 1681 and went through the resistance checks. The checks required verifying that a short to ground did not appear at a particular point, but did not specify the resistances you should see. All the checks passed but I was concerned about one resistance measurement which was about 3 ohms. That seemed awfully close to a short, and I spent about an hour tracing through the schematic before finding a 2.2 ohm resistor between the line and ground. Everything was okay.

The next phase was the initial voltage check. The 1681 is wired with a 3-wire AC cord, with the chassis grounded. I guess by the 1980’s this was already common practice. Older gear I have refurbished has come with 2-wire, non-polarized plugs – these are extremely dangerous, and the first thing I do when I find those is to rewire the gear with a 3-wire cord, chassis ground and inline fuse in the AC line. Not required this time, just saying…

So I powered up the PS-23, and did a careful check of the voltages supplied at the 11-pin socket. Everything looked good (I had already made the change for the 275 vdc low plate voltage) so I hooked the power cable, and turned on the 1681. The beautiful dial lights lit up red, and I immediately noticed a sizzling sound coming from the dodgy home-made cable. I don’t know about you, but when I hear sizzling sounds coming from a cable carrying more voltage than the third rail of the New York City Subway on one of the wires, I think “Abort! Abort!” That was the end of Voltage Test 1. Happily, there did not appear to be any damage to the rig or the power supply. Magic smoke intact, it was time to find a replacement cable.

Back to eBay, where there are perennial offers of a pair of 11-pin sockets and a six-foot length of 8-wire cable (this turns out to be a WireMan product BTW) which includes a helpful scan of the wiring instructions from the PS-23 manual. Assembling the cable was straightforward, and in short order I had a correctly wired, non-sizzling power cable for the HX-1681.

New cable and plugs

New cable and plugs

The initial voltage tests passed. This was the exciting moment, the first time I would try to load up the transmitter. Following the tune up instructions, I placed all the controls in the correct settings, and took the first step. Placing the meter in Ip position, and switching the mode switch to Tune, I should see the meter point to an indicator mark showing the correct idling plate current…..

Nothing. Nada. No meter deflection. Arrrrrrrrrrrrgggh!

Okay. I powered everything down, and gave this development a little thought. The easiest thing to check would be the tubes in the final. One 12BY7A and two 6146‘s. I pulled the tubes and tested them on my Hickok 6000a tester – they were perfectly fine, happy little tubes. That wasn’t it.

In thinking over what I had already checked, I realized there was one resistance measurement I had not bothered to make. There was a footnote in the resistance check instructions that that stated with the meter in the Ip position, and the mode switch in the Spot position, one of the outputs from the VFO should be at ground. I had not checked this, since most of the resistance checks were to insure that there was not a short to ground at the test point. I made the neglected test, and instead of a short to ground, I had an open – infinite resistance. There was something wrong with the switch!

Pulling out my trusty can of Radio Shack Control/Contact Cleaner and Lubricant, I went after all the switches and pots in the rig. My technique is the nest each control in a wad of paper towelling on all sides, and then literally blast the crap out of it while moving the control through its entire range repeatedly. This cleaner foams up a la Scrubbing Bubbles for electronics, and I have had good success with it before. The key is to be sure to mop up any excess; let the control sit for while and then wipe it down again. It’s a good idea to check the next day for any residue which may have seeped out.

After the control cleaning exercise, everything worked fine. The plate idle current looked a tad low, so I adjusted it according to the manual, and after that the meter indication was spot on. I did not re-neutralize the tubes or realign the output, and these steps did not appear to be necessary.

It's alive!

It’s alive!

After figuring that out, there was one more small issue to deal with. The HX-1681 manual describes a simple mod to the HR-1680 receiver to better match audio levels for the sidetone produced by the transmitter. This involved changing a 33k ohm resistor on the audio board of the receiver for a 100k Ohm value, and adding a 10k ohm resistor in series with one on the audio lines to the volume control. I found both these resistor values in our local RadioShack in Oneonta NY, and made the change “in the field” so to speak, as the receiver was already at my upstate QTH.

I was ready to install and test the transmitter with its companion 1680. I needed three shielded male-male RCA phono plug cables to connect receiver mute, sidetone, and receive antenna. Although the manual calls for coax with phono plugs to connect the receive antenna, the shielded audio cable (also from RadioShack) seems to work fine; I’ll replace it with coax if I notice any problems. The initial tune-up into a dummy load went well, but I was a little disappointed to hear hum in the audio out when the transmitter was keyed. On a hunch, I grounded the transmitter and receiver chassis together, and the hum disappeared.

My habit is to use an end fed half wave antenna cut for 40 meters, with a 4:1 balun and a manual antenna tuner at the upstate QTH. This works fine with my modern solid state rigs, but the setup is a bit cumbersome for use with output tank of the a tube transmitter. There is a concern that there might be harmonics in the output that are stronger than the current FCC regulations allow; these are more stringent now than when these tube transmitters roamed the earth. Using a resonant antenna is best, but a tuner also helps clean up the signal.

The problem is the chicken-and-egg relationship between the transmitter output tank and the tuner. When you tune the transmitter for maximum RF out, you are adjusting the tank to load to whatever it sees. If that happens to be an antenna tuner that you then adjust for lowest SWR, you are de-tuning the transmitter tank…

Here’s my solution to this conundrum (since I really can’t set up a resonant antenna given the configuration of my upstate shack): I load up the transmitter into a resonant dummy load, back off the plate current a lot, then switch to an auto-tuner connected to whatever antenna configuration I have set up. When all the chatter subsides, the auto-tuner has got my “random wire” looking as resonant as it’s going to get. I can then bring up the transmitter power and tweak the tank. The perfect fusion of retro and space age technology.

With everything installed and working,  it turned out that propagation was not great that weekend with minor magnetic storms going on. I did see my signal in RBN, so I know I’m getting out. There just wasn’t enough time that weekend to make a QSO though.

RBN can hear me!

RBN can hear me!

There will be some further embellishments on this station in the coming months, but I’m pretty excited. There are lots of retro radio events coming up: Straight Key Night, Novice Rig Roundup, the Classic Exchange and others. I am really looking forward to putting my twins through their paces.

73
de N2HTT

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