With my JBOT amp ready for installation, it was time to go back and check out the rest of the circuitry on my old Azorean DSB/Direct Conversion 17 meter "Magic Carpet" transceiver. I was surprised to find that the oscillator, well, wouldn't oscillate. The MPF102 that I had in the main oscillator circuit was blown. I suspect voltage spikes from the T/R relay. I installed the required diode across the relay coil. (I seem to blow up a lot of MPF102s. Is it just me, or are these devices really fragile? They are junction FETs, not MOSFETS, so I thought of them as being more robust. But I seem to go through a lot of them.)
After messing around with the oscillator and buffer circuits, the nice clean Manhattan isolation pads that had been there at the start were all messed up, with big piles of solder with the ends of multiple axial leads stuck in there. I decided to start afresh. Out came the little PCB box that housed that housed the oscillator, buffer and amp stages. Off came the walls of the box. (When I built this thing the first time, I didn't realize that I would need an amp to get to the 7 dbm needed to drive the diode ring. I ran out of room on the main board and ended up building the needed amplifier on the back wall of the box!)
So I got to build this little circuit again, ten years and three countries after the original build. It was fun. I like building oscillators. There is that satisfying sense of closure and completion when, at the end of the effort, you turn on your receiver and hear the tone from your creation.
There was also a fun little bit of troubleshooting. After rebuilding the oscillator circuit I noticed that applying power to the "on the wall" amplifier caused the oscillator to shut down. At the buffer, I was seeing RF in and RF out, but the whole thing would shut down when I powered up the next stage. Obviously there wasn't a lot of BUFFERING going on! Sure enough, the MPF102 was bad. I replaced it from my dwindling supply, and all was right with the universe.
Now the amp goes in. But first I will build the low pass filter. I promise.
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics"
http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers:
http://www.cafepress.com/SolderSmokeOur Book Store:
http://astore.amazon.com/contracross-20
Maria wanted to go with a mathematical theme for this year's Jack-0-Lantern. Pumpkin Pi!
Temperatures dropped over the weekend and I had to fire up my new heating system for the SolderSmoke shack. See above. Heating by Heath, Halli, Hammarlund and Drake (sounds like a law firm doesn't it?). I'm happy to report that those old filaments take the chill off quite nicely while adding a nice aroma to the room, along with some very pleasing lighting effects (I especially like the green glow from the DX-100 tuning dial).
I'm a big fan (wanna-be really) of The Royal Society. In SolderSmoke 138 I noted that Isaac Newton (former Society president) seems to have had The Knack. And when I was in London one of the major perks of my job was that I occasionally got to visit the Society's headquarters. Bill Bryson recently edited a book about the Royal Society -- in his intro he noted that they have always been a very international group (just like us!)
With my JBOT amp ready for installation, it was time to go back and check out the rest of the circuitry on my old Azorean DSB/Direct Conversion 17 meter "Magic Carpet" transceiver. I was surprised to find that the oscillator, well, wouldn't oscillate. The MPF102 that I had in the main oscillator circuit was blown. I suspect voltage spikes from the T/R relay. I installed the required diode across the relay coil. (I seem to blow up a lot of MPF102s. Is it just me, or are these devices really fragile? They are junction FETs, not MOSFETS, so I thought of them as being more robust. But I seem to go through a lot of them.)
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics"http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics"http://soldersmoke.com/book.htm
(From the November 2004 issue of QST)
Just click on the article and use the zoom feature of your browser to visit the teenage shack of Yardley Beers. 
How's that for a beautiful homebrew rig! Prompted by our discussion of distinctive ham radio names, Harv, WA3EIB, sent us a very nice report on Yardley Beers, W0JF. The rig pictured is Yardley's "Jason" 20 meter QRP transceiver. Yardley had named the rig for his cousin. Harv met Yardley at a Colorado hamfest in 1993: 
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics"http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20
Posts
