EMRFD Message Archive 9467

Message Date From Subject
9467 2013-12-01 17:41:01 mm0gyx 602 oscillator
Hi folks,

I'm building the 602/386 basic dc receiver from figure 1.9 page 1.8 in the book.

I haven't installed all components yet as I wanted to power up the 602 alone to check the frequency stability using the capacitors I've used so far. I have applied 8 volts (it's what I had available) and have used 680pf C0G caps for the 2 in the emitter/base divider.  I also used 2 of the same in series to instead of the 270pf in the book, so far I figure I'm up to 680/4 = 170pf. I used a 20 turn, 25 swg on t37/6 toroid for about 1.2uH. Finally I inserted a 33pF NP0 parallel to the toroid.

I worked out my total nominal capacitance to be 203pF and with 1.2uH, I get a resonant frequency of 10.12 Mhz. When I tuned the big rig and went searching for it, I finally found the oscillation at 8.23 MHz.

I know the capacitors will have some variation and maybe there's stray capacitance from the build (used ugly with short-ish leads) but with that Fres and assuming 1.2uH the capacitance works out at 312pF.

So, does that sound reasonable? It seems a long way out.


9524 2013-12-05 06:24:28 mm0gyx Re: 602 oscillator
Please disregard this message, I made an obvious error. It struck me later in the evening.

Frequency now within 5% of theoretical.