Touchy Circuit..?

[K9STH]

The late Jack Camp, W5HS, liked to home brew all sorts of equipment. He was usually on 50.700 MHz every morning using his mobile rig talking with the same group of Collins and Texas Instruments employees on their way to work. Now, if you wanted to work him from his fixed 6-meter rig you had to call him on the telephone, Then, he would get out his clip leads to hook up the various voltages to the transmitter. Each connection required a certain clip lead and that particular lead had to be placed in a specific location.

Basically, the transmitter required certain stray capacitances and inductances to work properly! If any lead was "out of position", the transmitter just wouldn't work!

He was a test technician at Collins Radio and was capable of some very precise work. However, for his own rig . . .

Glen, K9STH

[SM0AOM]

Varactor or step-recovery diode frequency multipliers...

73/
Karl-Arne
SM0AOM

[WB5WSV]

After successfully building a crystal oscillator using only a resistor, a crystal and a 7404 TTL chip and being very impressed with it, I found the design for a VFO that used a 7403 TTL chip. I built that and tried it out. Now talk about touchy! One little touch of the pot and .... zing! ... it would be a couple of MHZ away. I added a fine tuning pot to go with the course tuning control but finally realzied that it would be to touchy to use for anything practical.

As far as kits, my TenTec 1254 looks like a brilliant design, potentially an R-390 the size of a scanner. But setting the VCOs was nightmarish. A couple of trips up and down the coil and the coil slugs would be so worn out you could not get them to move any more. I replaced the coils and the 2nd time put a piece of rubber band down through them to give the slugs more purchase., That helped a bunch but I was never able to get the thing to perform very well except right in the middle of the freq range. At 15.00 MHZ it was fine, and tuning in SSB was a breeze. But down in the 100 KHZ-2mHz range it was terrible, with so much noise as to be unusable. And at the upper end, 25 MHZ or so up, it was all but deaf.

One day I decided to crank it up and see if I could figure out how to realign it and maybe solve the problems. And it was deaf everywhere.
A few tests showed the PLL had quit, and the characteristics showed it was likely the chip itself. I put it plastic storage box and there it has sat for several years now. Maybe one day I'll get back on it, but I think a key aspect of maturity is knowing when to quit.

Robert
WB5WV