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I need help adjusting transmitt frq of a "coiless fm bug"

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I have this really nifty no coil - no trimmer fm mic that i built from the somewhere on the web. It works great but, the circuit can only transmitt on a fixed frq. The transmitter works on 3 main components and a few others. They are IC-CD4069, BB109 varicap diode and a 10.7mhz ceramic xtal. PLEASE HELP. Can i maybe bias the diode. Many thanks. If u wish to view it the address is http://www.electronic-circuits-diagrams.com/radioimages/radiockt8.shtml


I would think you can very the freq. by loading the xtal with a parallel capacitor. A series coil would also bend the freq., no?
Adding a tuned circuit at the antenna would clean up the output some.

Edit: It's not a crystal actually but a filter but it might still be bendable. You might try to replace the filter with a crystal.
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I've seen that before.

I agree with Nigel, it's a very poor design because it will transmit at every multiple of 10.7MHz up to a couple of hundred 100MHz.

If you're going to add coils then why not just build a properly designed FM transmitter with coils?
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New Member
Forum Supporter
Or at least add another transistor stage with a tank circuit tuned to 96.3 Mhz. That way you'd get more range with very little frequency drift and it wouldn't be spraying all over the spectrum.


New Member
It transmits on maybe fifteen different frequencies at the same time, is this not enough? :D


Well-Known Member
All I can see on that page is a big ad that covers the content.
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