Two FM circuits

[Integrator741]

Hello everybody,

I am trying to do small home FM transmitter project. I found two circuits in the internet and I am struggling to find the difference between them (besides transistors).

Circuit number 1

Circuit number 2

And also which one would be more efficient?

Thank you for your help,
Integrator741

 

[duke37]

The circuits are similar.
Circuit 1 has AF and RF power supply bypass, this should be be included in Cir2
Circuit 2 has a capacitor in series with the aerial, this is good.

The 2N3904 may be a better switch so the efficiency of Cir1 could be higher.

 

[Integrator741]

The circuits are similar.
Circuit 1 has AF and RF power supply bypass, this should be be included in Cir2
Circuit 2 has a capacitor in series with the aerial, this is good.

The 2N3904 may be a better switch so the efficiency of Cir1 could be higher.

So how would you calculate the efficiency of the circuits?? Is there any specific formula to do it?

 

[davenn]

So how would you calculate the efficiency of the circuits?? Is there any specific formula to do it?

not really, you would have to look at each section in turn

both these circuits are designed for low power output maybe ~ 5 - 10 mW
for use over short distances , 50 - 100 metres max, depending on terrain, buildings, trees etc

over that range you are probably unlikely to find much difference between them

Experiment!! build them both and see how you go, do some actual real tests

Dave

 

[Integrator741]

thanks

 

[CDRIVE]

Not surprised when simulating circuit 1 it failed to maintain oscillation. It kicks on but decays exponentially. It doesn't mean that this circuit is faulty. It just means that sinusoidal oscillators are always a royal PITA to sim.

Chris

 

[philgritsr2]

I built this one and the range was about 350 feet very easy to put together and because of voltage regulator fairly stable after about five minutes of use guess it had to warm up a bit then do drifting at all good luck

http://www.techlib.com/files/fmxmit.pdf


thanks Phil

 

[philgritsr2]

also built this transmitter, these are the videos that helped me put it together. the man in video is very nice and even responded to emails I sent him he has lots of neat projects

thanks Phil

 

[CDRIVE]

also built this transmitter, these are the videos that helped me put it together. the man in video is very nice and even responded to emails I sent him he has lots of neat projects

thanks Phil

"The Shadow"! That brings back great memories of listening to those broadcasts on my crystal radios in the 50's.

Chris