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We dont seem to have places where you can get cheap stuff in Britain.
I tried to buy a spectrum analyser from ebay last week, good job I didnt pay it was a con artist. Problem is with kit like spectrum analysers is that you need something capable like an HP, otherwise its can be next to useless. And everyone seems to know the value of an HP856xrange unit, being $4000+! I did once go to a ham radio show just outside of london, nothing cheap there though. Though I will remember two enthusiastic bearded men who were each looking through boxes of junk at opposite ends of a stand, they had their head in their boxes and were talking to each other on radios..saying "bill theres some good stuff in this box, over", "george..yes Ive found some great stuff in here, over"! Meanwhile...I have a 612 based colpitts oscillator which on test works at 110Mhz with 10pf base/emmiter and 22pF to ground on the emmiter. But curiously jumps up to 210Mhz when I double the 22pF cap to 44pF. Ive got a frequency counter via a FET buffer showing those frequencies, and (with the counter turned off) I can verify the frequency with my portable scanner set close by. So increasing the capacitance doubles the freq of operation!? I do wonder whether the spectrum has just spread into harmonics...but i cant find them on my scanner...and wheres that HP spectrum analyzer..hmm If anyone out there knows why increasing the emitter ground capacitor in a colpitts will increase the frequency I would be very happy to be educated! Given that the freq should be the emitter ground cap in series with the emmiter base, in parallel with the inductance. Which is 100nH, with a 1/2PI ROOTLC tuned circuit relationship. Happy happy happy... |
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