The title held a lot of promise, but the subtitle ("A Search for the American Character") hinted at the main problem that I had with the book: the author (perhaps driven by his editor) seemed to be struggling to prove that there is some uniquely American elements to amateur science and technology. Early on, Mr. Hitt, makes the preposterous claim that "the rest of the world doesn't have amateurs." He goes on to write that "In Europe and on other continents, the word hints at class warfare... Amateurs may be taken seriously, but, almost by the power of the word, are kept in their place: isolated outside some pre-existing professional class, some long-standing nobility. In America, amateurs don't stay in their place or keep to themselves." What a load of rubbish! This claim directly contradicts what many of us have been finding out in the quintessentially amateur world of amateur radio: as we travel around the world (in person, or via the ionosphere) we find, all around the globe, guys who have followed shockingly similar paths to ham radio. From Sudan to Switzerland, from India to Indiana, the story is much the same. And I'll bet you'll find similar similarities in just about every serious sci-tech hobby (astronomy, photography, etc.). To claim that there is something fundamentally exceptional about amateurism in the U.S. is, I think, ridiculous. Mr. Hitt should have spent some time looking at the amazingly diverse and vibrant world of British amateur science and technology. That alone would have prevented him from straying into these silly claims of American amateur exceptionalism. But, all that aside, there is a lot of interesting material in the book. I liked his description of John Dobson and the amateur telescope builders. And, somewhat surprisingly, Hitt's description of the DIY Biology movement (these guys are playing with genetics and cooking up new organisms) seemed to capture very well the creative joy and satisfaction that amateurs find when working (just for fun) on their projects. I was kind of surprised when I found myself identifying with the DIY Biology folks. Their basement labs sounded a lot like our radio shacks.
I've been kind of cheating with the audio output from my BITX17: I've been using one of those little battery-powered computer speakers. It sounded fine, but hey, this is supposed to be a homebrew project right? I've already noted my ideological objections to the use of the LM386 CHIP. The files of the BITX20 yahoo group provided a very promising and completely discrete AF amp circuit by Arv Evans, K7HKL. I used a 2N3906 and a 2N3904, with a 2N2222 driving them. It works like a charm. Not a bit of feedback or motor-boating. It sounds great. I've already had a contact with it: Jack, W7YUM is a builder of big amplifiers out in Salt Lake City. He seemed very impressed with the BITX concept so we may have a Utah BITX in the works.
Wow, it is very clear that the radio gods are pleased with my BITX efforts! I had my first QSO on the new rig today. And it was with a station in my old home, the place where I got my start in 17 meter homebrew phone: THE AZORES! CU7MD. Very cool.
I was having trouble with the mic amp on my new Manhattan Discrete BITX 17. I had it wired as per the schematic, but it just wasn't working right -- I was getting very little DSB out of the balanced nodulator, but everything worked fine if I 1) unbalanced the bal mod or 2) injected audio (from a sig generator) directly into the audio in port of the balancec modulator. Clearly something was wrong in the mic amp circuit. I noticed the collector voltage seemed quite low.
As Nicolae noted, the 10K value may have worked with lower gain transistors. We must remember that BITX was (very admirably) designed for minimal cost and maximum use of scrounged parts.
I swapped the 10K resistor for a 39K and all is right with the world. The band is not yet open here, but I bravely called a European aeronautical mobile station, hoping that he would be my first QSO on this rig. I think he heard me, but no QSO (yet!).
Good news on the BITX. I think I have solved the low frequency oscillation problem in the power amplifier. I tried running the PA off a separate power supply -- the oscillations disappeared leading me to conclude that the feedback was taking place via the power supply lines. I put a 22 uF cap to ground from the top of the PA's RF choke. With this cap in place I can dispense with the separate supply kludge. The amp is stable.
This morning I also resolved a different stability problem. I'm using a relay for T/R switching. One set of contacts controls the DC power, the other set was supposed to disconnect the receiver input from the antenna/lowpass filter when on receive. But I had positioned the relay too far from the LP filter and RX input, so I ended up with this long piece of coax that was hanging off the PA output terminal and carrying lots of RF on transmit. Yes, this led to oscillations. I thought about repositioning the relay, but I think part of the problem is that even if optimally positioned, the long unshielded contact levers inside this relay would be radiating a lot of RF and causing stability problems. So instead I put a small reed relay very close to the PA out and RX in connections. It carries the signal to the receiver when in R mode, and disconnects the RX when in T mode, without any long coax lines or unshielded relay levers. It works.
I still have a few things to do: -- I need to build a proper speaker amplifier so that I can dispense with the amplified computer speakers KLUDGE. -- I need to get a 3 pole double throw switch and some crystal sockets so that I can switch crystals from the front panel. Three rocks will cover all of 17 meter phone. -- I have to build a case for this rig. I'm thinking wood, with tin or aluminum sheeting glued to the inside (for shielding).
do Richard Feynman and the G-QRP club have in common?
answer is an annual pilgrimage to Ripponden in Yorkshire, England. The G-QRP
club have their convention in a local school and Feynman went there every summer
to visit his wife's family. Here's an interview with Feynman filmed at
the Old Bridge Inn which is about a mile from where the G-QRP club gather:
I found a quote from Doug DeMaw that I wanted to share. This one seems appropriate as I struggle with unwanted oscillation (and as Halloween approaches). From the January 1986 QST:
"Self -oscillation occurs not only in the low-frequency and high-frequency spectrum, but it often takes place at audio frequencies! I have actually heard the transistors "screeching" when strong audio oscillations were taking place in a homebrew transistor power amplifier. On one occasion I could see a bluish glow coming from within the transistors (visible through the ceramic heads of the devices) during a period of instability. Needless to say, the transistors self-destructed."
I've been having some instability problems with my BITX 17 IRF510 final. But I think I have the problem identified. I was getting low frequency oscillations (around 100 KHz). Tonight tried putting the IRF510 on a separate power supply. The oscillations ceased and I am getting a nice clean 3 watts out. So I'll go back and beef up the decoupling on the power supply lines.
As you can see, the board is starting to fill up. I really like it. It seems (to me) like the canvas of a painting approaching completion. This morning I put in the T/R relay. That space in the upper left is reserved for the driver and the IRF510 Power Amplifier.
I got some help from the Chief Designer this week. As noted in an earlier post, Farhan advised me to check the mixers. I knew that I had them wired correctly and that they were in fact mixing, but when Farhan advises you to check something, YOU CHECK IT. Farhan was right (see earlier post).
It really sounds great. I know that the filter still has significant ripple in it, but the receiver sounds so good I'm reluctant to mess with it. Should I de-ripple it?
On the train yesterday I was thinking about this rig, and it occurred to me that my 23.1 MHz VXO/ 5 MHz IF arrangement means that this 17 meter transceiver could also generate signals on the 10 meter band. Of course, I'd have to build a second bandpass filter, but the radio gods guided my hand and caused me to leave space on the board for just such a filter (see above). I realize the IRF510 PA wouldn't be too good up at those frequencies, but when the radio gods speak, you have to listen.
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!)