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4W FM Tx


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Hi Knownothing,
I guess you built this project:
http://www.electronics-lab.com/projects/rf/001/index.html
Sure, it will have temperature problems if its antenna is the wrong  impedance or length, or if the whole circuit isn't "aligned" (tuned) properly.
Use its minimum supply voltage of 12V and make certain all its tuning parts work to produce a peaked output. If an adjusted part doesn't produce a peak, maybe its coil needs to be stetched or tightened. The output transistor should have thermal grease on it, under its heatsink.

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Dear Knownothing
I have built the 4watt Tx and it wotks well. the only Transistor that gets hot
is TR3 and needs Heatsink.
The other Transistor tempreture is normal and is because of the Frequency they are working.
But My Tx Problem is that its frequency sometimes changes when I Disconnect the 12V Power supply and connect it again.

HTH - Shahriar

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I had built the cct many many years ago and worked fine.

You must check first the 3 resistors if are of the correct value. R3 & R4 are both 10K. In case you made R4 = 1K then Tr1 will overheat.  Is R5 = 82 Ohms?  You can increase this value up to 120 Ohms without any significant reduction in performance.

Check if the transistor oscillates.  If not then inspect all the capacitors around it, C5,C7, C15, C6.  C7 and C15 are the components that affect oscillation.

Last thing, check the pollarity of the transistor, emitter-base-collector.
Regards
P.

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