FM transmitter, what's a matta' wit it?

[panic mode]

About crackling, it is probably distortion created by either mic or preamp
(components around Q1, everything from C1 to C2). To verify of the problem
is mic, simply remove mic and R1. Put small 8 Ohm speaker (like from
transistor radio) instead of mic and see how this works.
If this didn't help, I would suggest to completely remove R3 and connect R2
to base and collector of Q1 instead of current setup. Add small cap
(4.7nF) from base of Q1 to +9V to remove any RF feedback and add small tantal
(10-22uF) accross battery. That should take care of wasted
battery, at least for a while.

 

[zachtheterrible]

Well, I figured out the problem, it's just that I'm listening to harmonics, not the actual frequency. I'm getting closer to the right frequency, but if I decrease the value of C4, say from 40 to 4, that will increase the transmitting frequency, right?, or wrong?

 

[Russlk]

Right!

 

[zachtheterrible]

I found out what happened to C3. I burnt it out while soldering. I've done it twice now. Anyways, the transmitter works great, I can hear it from 1/4 mile away! There's a tiny bug with C4 though. I used just a regular ceramic capacitor in place of a tunable capacitor. I had values around 1-5 pf that I tried, and they worked great. Now I have a tunable capacitor that goes from 0-4 pf; that doesn't work. When I turn it, it will make the radio go silent, but I can't hear my voice. Any ideas??

 

[panic mode]

It means the oscillator part is working but there is no modulation.
In other words audio signal doesn't get to the oscillator stage
through C2. Either you forgot to connect mic or the preamp with Q1
is not working.

 

[zachtheterrible]

The funny thing is, it was working GREAT before I replaced C3 w/ a tunable capacitor. Can anyone give me a way of troubleshooting this thing w/o desoldering n puttin in new components? Also, there is absolutely NO possibility that the circuit could be connected wrong, I've checked it over various times.

 

[zachtheterrible]

Maybe I fried something again while I was soldering???

 

[zachtheterrible]

Nevermind, I figured the whole thing meself. It was just a bloody loose connection on my microphone. Anyways, I've got me another question. What would I add to this circuit to lose the harmonics? And what is it called?

 

[Nigel Goodwin]

Nevermind, I figured the whole thing meself. It was just a bloody loose connection on my microphone. Anyways, I've got me another question. What would I add to this circuit to lose the harmonics? And what is it called?

You would need filtering on the output, you would need the transmitter in a sealed metal box, with the aerial fed out through filters - like a 'proper' transmitter!.

It's hardly worth it for a simple bug like that one.

 

[zachtheterrible]

Thanx all for ur help, you've all been a lifesaver!!