I’m Baaack! Dusting off the station. And, the SW-40 is on the air!

Completed SW-40 kit board from Dave Benson K1SWL

Completed SW-40 kit board from Dave Benson K1SWL

I am back to the blog after an almost 1 year hiatus from all forms of ham radio! It’s good to be melting solder once more. Really, really good!

During my down time, I have seen hits to my blog every so often. Someone seems to find my blog and read several entries, maybe looking for some clues in whatever project they’re working on currently, or just to satisfy their curiosity, boredom, or whatever. I’m glad it seems to still be useful or interesting to some out there. Because I don’t post anymore, I’ve lost any kind of regular following, which is understandable. Still, I’ll pass this blog entry along to Bill Meara of SolderSmoke in case some of his friends might enjoy the entry.

I had stuffed the kit board for the SW-40 last August but I was missing the PA transistor, a 2SC2078. I think I had stolen one from this kit to replace one I’d managed to blow up in the SW-20 some years ago. No worries. Some web browsing had found a supplier and the part (and some spares) arrived about a week later in the mail (I had none in my junkbox and due to the low cost I wanted to just use the intended part rather than make a substitution).

Unfortunately, my time was extraordinarily limited in both the fall and spring. I had ZERO time to play on radio. All that time, the kit, and my radio hobby life, sat idly by on the bench, untouched. I would occasionally look across the room at it, longingly, remembering happier days when I could play radio! It was sad to be honest. But I knew eventually I would find an opening again to play. And, come May 2016, I finally did.

When the dust settled in my schedule, the first order of business for me was to do some late spring antenna work (an SW-40 without an antenna is not too useful). I think many of us play antennas during the warm months of the year (at least those of us who live in colder latitudes).

I found that some severe windstorms had spun my 17 m dipole around on its mast, and it was beginning to torque the coax feed. The U-bolts normally hold quite well but I’m using a cheap plywood mast-to-dipole plate, and after a year some slack had developed, allowing the dipole to rotate a bit. This was solved by running a pair of bolts through the plate and mast. If any rotation takes place now, it will happen at the base of the mast, which can be easily corrected.

The longwire/tuner arrangement I use for most of the HF bands had held up perfectly. The homebrew tuner (see earlier blog entries for that!) is protected from the elements by a Rubbermaid “Roughneck” plastic tub, and it has done its job. The longwire had sagged slightly, which was easily corrected. I set the controls for 40 m CW and had under 1.5:1 VSWR, just like a year ago.

Feeling the ham radio mojo starting to return after the antenna work, I finally came back to my workbench.

This is no simple thing. Having been away for so long, it took me some time to remember what was what. I felt like I’d been in suspended animation and was just coming to.

Even approaching the work area after such a long time away seemed like some type of religious experience to me. As I rediscovered where things were again, the excitement began to build. I really wanted to finish this little rig and get it on the air.

The long-dry yellow sponge of the soldering station once again found water. The iron was switched on. The Kenwood TS-2000 behind me was turned on to listen to the background banter of hams on 40m. I was back in business.

I soldered in the PA transistor, found some pots for volume control and tuning in my junkbox, and soldered up some leads for a key. I did the “smoke test”, applying the 12V DC. And…


No smoke, but no signal anywhere on the 40m band. I double checked my cabling and my monitor rig and tried again. Still nothing.

The current draw was very low and barely changed from RX to TX, which is a very bad sign! It was at this point that I felt some frustration creep in about the manner in which the kit was built and NOT tested, stage by stage, which is what I normally try to do. Because of limited time last summer, I had simply thrown all the parts into the board and crossed my fingers. Let this be a lesson to those novice builders out there! This is NOT the way to go!

Fortunately, I guess, this (and probably most of my near-future radio projects) are simple enough and I’m familiar enough with the circuits that troubleshooting is not that hard. In fact, having it NOT work right away provided a mystery. And forced me to go back, stage by stage, to investigate my creation. Which was what I should have done before anyway.

The scope, which I’d not touched in a year, was activated. Dave’s kit has excellent documentation which actually has almost all nodes of the circuit annotated with both the DC and AC expected signal levels! This almost seems like cheating to me! But hey, it’s there and I used it.

I went back to the LO. No troubles there, a very solid signal around 3 MHz from the Colpitts. Then I checked out the 4 MHz oscillator of the NE602 chip of the TX mixer. Again, solid 4 MHz signal and the voltages checked out. EXCEPT — it died before it reached the input of the following buffer stage and “Q4”.

There are two IF cans, T2 and T3, between the TX mixer and the following buffer stage. The signal was fine on the primary side of T2, but something happened to it by the time it hit the secondary of T3. It was around 500 mV p-p when a 1.5 V p-p was expected. I found out that the capacitor C32 in parallel with the secondary was not the right value. Somehow I’d put in a 150 pF instead of a 47 pF. The change must have resulted in more RF getting shunted to ground, and very little was left to apply to the base of Q4. Once swapped out, I was able to tune T2 and T3 and…voila! The SW-40 came to life!

I was able to get 2.5 W out of this rig, which is the upper range Dave cites as the expected output (1.5 – 2.5 W). That was very satisfying. And the signal is clean as a whistle on the scope.

I was thrilled that the RX side worked fine, first go. I recall that I HAD actually tested some of those stages as I was building the kit, so that probably helped me there. Signals poured in to the little rig immediately and at loud amplification. How thrilling! There is always something special about “first light” for a creation of your own, even a kit.

I feel that the troubleshooting aspect of getting the rig on the air helped to make this kit feel more personally connected to me. Had everything just worked after stuffing the parts, I think part of me would still have wanted to go back through with the scope and measure the various signals coming out of the stages. It seems way too appliance operator-like not to. And all of Dave’s annotations of expected voltage just beckon the hobbyist to play.

What comes next is the boxing of the rig. I know some builders don’t really put their creations in much of a box. But I do like to sometimes take the rigs out camping or picnicking somewhere, and having it in a contained enclosure really helps! I purchased a box and a nice digital tuner kit from QRPkits.com last year, it’s the same one being sold for their Bitx kits (and the one I used for my Bitx17 I built two years ago, the KD1JV digital dial). Another option for a tuning “display” which I had used with my SW20 about 16 years ago was a kind of ingenious kit sold by Dave that would announce your frequency by sending CW through your headphones. It took up very little space. But I kind of like glowing numerals.

So, this one should be a sharp-looking little rig once completed. And I fully expect to make many CW contacts with it. Heading towards another solar minimum, it’s nice to have this old kit completed for a lower HF band. I’ll post a blog once this is boxed.

That’s it! Nice to be back in the “brotherhood”, at least in some small way.




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2 Responses to I’m Baaack! Dusting off the station. And, the SW-40 is on the air!

  1. Nice work Bert, welcome back to the hobby. Troubleshooting a rig makes it personal for sure.

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