With the 20 Meter Oscillation Exorcism behind me, I have decided to take a break from electronics and do bit of woodwork. I took the walnut (I think) box that I bought via Amazon and cut out a big piece of the wood on the front. That's where the rectangular piece of copper clad board will go -- it will be the front panel, supporting the AF gain control, the bandswitch, the main tuning control, and the mic jack. A similar copper clad board will be on the back, this one supporting the antenna jack, speaker jack and 12V input jack (with space for a linear amplifier T/R control jack). (George Dobbs, G3RJV, calls this the "socketry.")
That beautiful copper sheeting will line the inside of the box.
I found the soft wood on this box to be very easy to work with. The little saw pictured above made the woodwork easy.
I have boiled linseed oil and clear polyurethane for the finish.
The transmitter was working fine on 40, but was horribly unstable on 20. In the past, this kind of thing would really drive me nuts, but experience has made me more patient. I know that "taming the beast" is part of the homebrew process.
I knew that layout was part of the problem: I had significantly less room on the board with this rig than I'd had with the BITX17: the additional bandpass filter and low pass filter, and the associated relays, used up a lot of copper clad real estate. So by the time I built the PA chain, the inputs were too close to the outputs.
The fact that the rig was stable on 40 but not on 20 led me to believe that this was not a problem of insufficient decoupling. Instead, I thought that I was getting additional inductive feedback at the higher frequency.
I noticed that the instability disappeared when I put the 1X scope probe on the input to the first amp in the RF chain (Q14). That was an important clue. Looking closely at the circuit, I realized that the base of Q14 had a long lead (several inches) up to the low pass filter. I had experienced problems with this lead on the BITX 17 project and had cured it with a relay at the low pass filter -- this relay took one end of the lead out of the circuit on transmit, preventing it from becoming a little radiator. I used that mod in this rig, and figured that that cured the trouble. Wrong. The other end of that lead was still connected to the input to the RF power chain. It was picking up enough RF to send the PA chain into oscillation.
I put a SECOND relay at the other end of the line. That took it completely out of the circuit. And the instability disappeared. I fired up the rig and worked California on 20. Very satisfying.
I got the BITX 20/40 on the air this morning. The receiver has been working for a week or so, but as usual it was a bit of a struggle to tame the transmitter. I got up early this morning and started poking and probing. I played with the driver and final coils a bit. I had used the same trifilar toroids that I'd used in the BITX 17, but this rig didn't seem to like them. So I went with FT-50-37 bifilars -- that seemed to work better. That IRF-510 seems to put out about seven watts on 40. (I still need to tame the transmitter on 20). The 40 meter signal looked great on the 'scopes (RIGOL and Tek!). Shortly before 8 am I worked AD4SY who reported that I was filling his shack with booming audio. Life is good.
Carl (M0ICR ex 2E0TEC) saved the day with my Tek 465 -- he sent the replacement HV multiplier that put the 'scope back in action. (Ace Tek repairman Tad WA1FQO made the repair. Tad sells Tek scopes on E-bay -- check out his products: Search for fqo63 on ebay.)
Carl notes a number of similarities between our workbenches and recent projects. All he needs now is a Drake 2-B!
Alan Wolke said he'd be interested in my reactions to having both a digi scope and an analog scope on the bench. I can already see areas where one might be a bit better than the other. The Tek is better at watching a fast moving audio or SSB waveform. But the Rigol doea all kinds of math tricks. Check out the FFT function shown on Carl's page: http://iqrp.net/
I am very pleased that you finally got it working with the help
of brothers from the fraternity. Having listened to your latest Podcast I think
that must be your alter ego! I have A Tek 465, Rigol 100MHz DS1102E and have
built 2 Bitx, one for 20m and the other for right bands- using a DDS VFO (3 if
you include the 80m version by Steve Drury G6ALU - look up MKARS80) ...I also
have 2 copies of SSD!
My website is here: www.iqrp.net where you can see both scopes in my
shack and images of my Bitx and my Hans Summers WSPR beacon!
I have just returned from my local radio club social meeting
(the Radio Society of Harrow) and took great pleasure in listening to
Soldersmoke 158 whilst driving there ... half on the way there and the other
half on the way back.
Very best wishes from
London (where it is cold, wet and miserable !)
January 20, 2014 MLK Day. Tough winter. Shack heated by Heathkit. BITX 20/40 Almost done: Bandswitching arrangement. VFO construction using spreadsheets. 2N2222s wired in backwards! (CBE not EBC! Who knew?) Other amusing building errors. Crystal filter evaluation -- the G3UUR method. Sweeping a filter with an Arduino DDS. Building a BITX in LTSpice. New Rigol 'scope (now 100 MHz). Tek 465 REBORN! QRP HATERS -- They are out there! MAILBAG. BITX 20/40 dual band bandsweep
The homebrew phone QRP community has been waiting anxiously for the unveiling of Farhan's new design: The Minima. It is a general coverage transceiver with many innovative circuit features. It has an Arduino in it and an Si570. Farhan's write up of the design process and the construction of the prototypes is really interesting.
Our friend Bert is once again melting solder. And he has launched a blog. (SolderSmoke listeners will remember Bert as the advisor to the University of Virginia radio club. That was the club that had its HQ in some sort of nuclear reactor building. They put up a huge wire antenna, but then took it down when they realized bike riders could possibly, uh, run into it.) Bert has some interesting stuff on his blog, including an article on conductive paint and one on the use of mail boxes as antenna tuner enclosures. And he reports that he has dusted off a BITX 20 kit. Welcome back Bert!
Preston: Your use of the
term "First Light" is especially appropriate. I got the concept from a
wonderful book of that title by the author Richard PRESTON. I pulled it off the
shelf this morning, and, as my coffee was brewing, read this on the dust cover:
Light won the American Institute of Physics award in science writing. An
asteroid has been named "Preston" in honor of First Light. It is likely someday to
collide with Mars or the earth."
The book's glossary
defines first light as: "A technical term from astronomy signifying the moment
when starlight is allowed to fall on a new mirror for the first time." The
first light experience must, I think, be similar to the feelings we get when we
first allow RF to fall on the front end of a new homebrew receiver.
Congrats on the S-107 OM.
73 Bill N2CQR
From Preston Douglas WJ2V:
happy to report that my little novice rig (well it's not so little if you weigh
it) consisting of my restored circa 1960 Hallicrafters S-107 and circa 1959
KnightKit T-50 (with V-44) made our first QSO with a guy 20 miles away on Staten
Island. This was Saturday afternoon, in full daylight, on 40 meters. He was
also running vintage equipment (Heath) but running an SB-200 Heath linear. I
have no idea why he needed a linear on 40 meter CW, but he seemed happy with it.
I could easily hear his signal via leakage through my Daiwa cavity switch, so
it was a pretty powerful signal. The T-50 puts out maybe 20-25 watts full bore,
but it certainly works fine, and got a 569 signal report. The 9 part was
obviously the important one.
I had just turned on the equipment, so the
S-107 needed to be adjusted a bit during the QSO to allow for a bit of warm up
drift. It stabilizes ten or fifteen minutes after warmup. I had to use a
straight key as I have not yet built the little kit that interfaces solid state
keyers with old rigs. I'll get to it on a slow afternoon this winter perhaps.
But for now, a straight key is about the right speed for this setup. T/R
requires switching the antenna, the VFO to transmit, and the receiver to standby
for transmitting. Not exactly QSK. Since there are so many switches, it may not
pay to add an antenna relay switch to this setup. Besides, switching is part of
I did not get set up
in time for New Years, so missed the chance to operate SKN.
I learned about
first light from Bill Meara's podcasts. It refers to the first time a telescope
is used, but, as he says, it applies just as well to a new (old)
All of this was caused by a local ham
offering a Hallicrafters S-107 for ten bucks. Even with the few bucks needed to
put it right, I sure got my money's worth.
Regards guys and Happy New
Earlier from Preston:
I am pleased to report my S-107 is restored
to full function. Based on the build up of filth on it before cleaning, it is
also cleaner than it has been for many years. The greasy dirt (I shudder to
think what it was made of) in between the flutes of the control knobs has
succumbed to a toothbrush and detergent. Who'd have thought what a difference
clean controls would make in the overall appeal of a radio?
The S-107 was purchased without
negotiation from a local and fellow member of the Long Island Mobile Radio Club
for ten bucks. I cheerfully handed over a ten spot and drove home with this
On the bench, the tubes lit, and I
could hear a couple of AM stations, but it made an awful racket with 60/120
cycle hum. New electrolytic caps cured that. The chassis felt "hot" to the
touch. Resistance checks on the HV-to-AC sides of the transformer confirmed
that, thankfully, there were no shorts. On advice of some pros on this list and
elsewhere, I removed a cap and resistor from the AC line to the chassis that
Hallicrafters thought was a good idea. With a new three wire grounded plug, the
chassis was now cold.
Alignment was done with an
old Conar signal generator (my $1 victory from an old hamfest) and trusty Tek
465 with frequency counter connected to its rear connector. The double IF
transformers peaked up, and so did the front end compression caps on all bands.
And now, the radio really receives CW and SSB! With a simple dipole (my beam
seems to have gotten sick from Irene and Sandy) I get good signals on 80, 40,
and 20. Maybe next weekend I will have time to try the upper bands during
daylight hours. But, the signal generator suggests they should be
The ten buck receiver
needed ten bucks worth of electrolytics. And I needed to buy a little 20 buck
kit of Bristol Splined wrenches. (Nobody I thought to ask had a set to lend.)
They were needed because: Another Hallicrafters bit of wonderment is that the
setscrews in the control knobs need to be turned with these unusual wrenches
that look like, but aren't, hex keys. Well, I suppose I can say I have the
wrenches if I decide to restore another Hallicrafters. I hear Collins has them
I think I mentioned that I
had to restring both the band spread and main tuning with real dial cord.
Another three bucks, perhaps. So, my ten buck receiver is still a bargain at
around 40 bucks in all. And, I had a lot more than 40 bucks worth of fun. I
spent part of the afternoon just listening to the receiver, it sounded so good.
You know how it is when you first listen to a new receiver.
Now, next thing will be to
see how it does making contacts with a Knight T-50. I know the T-50 is not
quite QRP. I probably puts out about 25 or 30 watts.
This will be about as close to my
novice station as I am willing to fall. The original station had the T-50, but
no VFO (which came with the T-50 I have now); but the receiver was an S-38E,
which was, (collectors notwithstanding) a piece of crap. And it's dangerous
since it is really one of those transformerless AM radios in shortwave clothing.
No wonder I only made a handful of contacts with it as a novice. I have no
nostalgia for my old Hallicrafters S-38E. I hear folks recommend operating it
with an isolation transformer. I have a better idea. Don't plug it
I had so much fun with the S-107,
though, I am starting to think about restoring an S-108 or an
As reported yesterday I have the 20 meter receiver portion of my BITX 20/40 rig up and running. I decided to take a closer look at the crystal filter I built.
Here is my method:
1) Using an Arduino/DDS sig generator, I put 11 Mhz energy into the base of Q2 (the stage immediately prior to the crystal filter).
2) Using my Rigol 1052E oscilloscope, I measured RMS voltage at the output of Q3/Q3A (the stage immediately following the filter).
3) I looked at Vrms as I MANUALLY varied the input frequency in 100 Hz increments.
4) I took the results and plugged them into a spreadsheet. I then used the spreadsheet to calculate the db drop from the peak Vrms value (So I wasn't looking at insertion loss, just the filter shape).
I used 20*LOG(Vrms/276)
5) I ended up with the chart displayed above.
I have a few questions:
1) What do you folks think about my methodology for evaluating the filter?
2) Where would you guys put the BFO frequency?
3) I know the ripple looks ugly, but the receiver sounds great. Should I attempt to get rid of the ripple?
Here is the filter I used (as prescribed by the AADE software): I estimated Q at 10000 and used LM and CM values derived by the G3UUR method, and made no effort to match impedances going into the filter:
Here is what GPLA predicted. I estimated Rin and Rout values. That probably accounts for the difference between the GPLA prediction and what I measured.
There it is, my second BITX transceiver, this one for 20 and 40. Once I got the VFO sorted out, this one went together very quickly. Obviously experienced gained on the first project was a big help.
I followed Farhan's advice and characterized the 11 MHz crystals in the filter. Then I used the AADE filter design software to build a 3 KHz filter. Using my Arduino DDS signal generator and the new Rigol 'scope, I was able to do a manual sweep across the passband -- it looked very close to what was predicted by the software.
This morning I built the bandpass filter for 20. As soon as that was done, I fired up the receiver. This was an amazing experience for me: a homebrew receiver that worked right away! That never happened before. I'm listening to 20 meters now. It sounds great. I even managed to demodulate and display some SSTV. The VFO seems very stable.
I still have to build the RF amplifier stages, the bandpass filter for 40 and low pass filters for 20 and 40 (I know Steve Smith is watching!). Then it will be time for cabinetry. I guess I should put some paint or varnish on that walnut box. Any recommendations? I'll line it (on the inside) with copper flashing material.
For the first time in years I got on the air on New Year's eve. I fired up the HT-37 and Drake 2-B on 20 meters last night right at 0001 UTC (well, with these rigs I should say GMT!). There was a moment of stress when, as I was trying to adjust the key, the whole thing fell apart and the little ball bearings spilled out. Yikes! It was as if the radio gods were trying to tell me something. It took me a few minutes to re-assemble my straight key, then I called CQ. The HT-37 puts out a lot more power than I normally emit, and it caused the Carbon Monoxide detector to go off, sparking a minor panic among family members. (See, this never happens with QRP!) With that resolved I had nice QSOs with K5KFK in Texas, W6VNR in California, and N1WPU in Maine. This morning I worked WA0ZDE in Missouri. The old HT-37 was drifting a bit, but Rick said he kind of liked that. (I put a muffin fan on top of the transmitter -- that should settle it down a bit). By the way, my key is a bit unusual: it is just a cheapo key, but I have it mounted on the base from a Vibroplex bug. I never mastered the Vibroplex, and ended up giving the bug parts to HI8G in Santo Domingo -- Gustavo planned on using them to fix another bug that had been given to him years before by Fred Laun (K3ZO).
Rick, WA0ZDE ( who I talked to on 20 this morning) sent me a VERY SKN photo collage (see below). I see that Rick also tends to hold onto his gear for a long time.
In response to popular demand, "SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
For the print version:
For shipping from a printer in the U.S. (probably better for N. American buyers) Click here: SolderSmoke USA Version
For shipping from a printer in the UK, Spain, or the USA (probably better for UK and other European buyers)
Click here: SolderSmoke EU Version
The two versions are identical, except for a minor difference in the paper used. That's why the prices are a bit different.
Bill's OTHER Book (Warning: Not About Radio)
Click on the image to learn more
W4HBK's QRSS Grabber: The Amazing Pensacola Snapper (Live!)