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how to calculate this FM Oscillators ?is the ceramic capacitor (beside 2nd transistor) in series ? ? Answered

Picture of

i can calculate it is by http://electronics-diy.com/calculators.php
but, is the 4.7pf take effect with the frequency ?
how frequency is it, if i change the trimmer capacitor with 20pf (i don't have the trimmer capacitor) ?
please help me : )

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steveastrouk (author)2010-06-09

Again, the 4.7 isn't critical to the design.

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Rendydevara (author)steveastrouk2010-06-09

yeah i know but, i have made (http://www.talkingelectronics.com/projects/Spy%20Circuits/images/Voyager-Cct.gif) WITHOUT trimmer capacitor (ONLY inductor 0.124uH,without 39pF), and i replace the 10pF with 20pF, i was calculate it L=0.124uH C on c-e pin = 20 pF F = 101.06 MHz is that right ? please help me, i confused i'm still 15 years old

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steveastrouk (author)Rendydevara2010-06-10

Just because you have a capacitor in a circuit doesn't mean it will affect the resonant frequency of the tank circuit. Equally likely is that the circuit will try and oscillate with the stray C around L1

Build it. Try it, use a radio with a digital display, tune the radio until you get maximum howl-round - read off frequency. That's the operating frequency of the transmitter. Play with it
Steve

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Rendydevara (author)steveastrouk2010-06-10

thank you very much. Rendy

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lemonie (author)2010-06-09

It's a while since I've picked through a directory-listing... but nowt in there.
How about this one instead:
http://www.josepino.com/circuits/index.php?fm_microphone.jpc

Note that the adjust is done with measurement it's the only way to be reasonably accurate.

L

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lemonie (author)Re-design2010-06-09

It's a bit more simple isn't it, and nice pics (the img embed didn't work though, ?)

L

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Re-design (author)2010-06-09

THe trimmer cap. is for adjustability. It will work with a fixed cap but you may not be on a clear part of the spectrum

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