I have a simple FM receiver circuit schematic that's tuned with a variable capacitor. How can I tweek it to receive frequencies above 107 mhz?

http://img413.imageshack.us/img413/8959/amfmradioxf6.jpg

I attempted a write over the blury text details of the components. Is this all the info you guys need? Is further filtering needed within the amplifier circuit redering my givens incomplete?

The schematic came out of an AM/FM radio kit I built when I was very young. I happened across the old instruction booklet stuffed away somewhere and ripped the page with the overall circuit out. The "explanation" below the schematic says the circled red FM portion recieves the signal and passes it to the AM/FM selector switch. From there a transistor amplifies the weak signal and then passes it on to an amplifier to power the speaker. Let me know if you need anymore info or clarifying.

http://img341.imageshack.us/img341/893/amfmradio2oy8.jpg

Here's the original without the markings.

Dude! Did that thing actually work?

The FM portion is tuned by a parallel-resonant (tank) circuit consisting of the 8pF, VC and the un-marked coil to the right of VC. In order to increase the resonant frequency you need to reduce the value of either the C or the L or both.

I'd start by just pulling out the 8pF capacitor. If that doesn't move it enough, you'd have to reduce the inductance of the coil by removing one or more turns. My guess is that it likely has very few turns, so perhaps even a fraction of a turn might do.

That, in essence, is the theory. Now for a few caveats:

Since your title mentions "Airband", I assume you want to receive aircraft radio signals. Be aware that aircraft radios are AM (amplitude modulation) not FM (frequency modulation). Also, broadcast stations (AM or FM) use high power transmitters, so receivers do not need to be terribly sensitive. Think thousands of watts or even hundreds of thousands for FM. Aircraft radios transmit with just a few watts of power... ergo very sensitive receivers are needed.

If you want to pick up police, fire and such, those are FM but narrow-band FM as opposed to broadcast FM which is wide-band.

Hope that helps a bit.

Airband frequencies are located between 108 and 137 mhz -- so i assumed if I raised the tuning on the FM receiver I could listen to them since it was the closest. If you need to rain on my parade and force me to go out and buy one of those special airband radios then do so. I don't feel like doing any tinkering for little or no reward.

And yeah, as I remember both receivers did work and worked quite well until I eventually ripped up the radio for spare parts. The FM portion was just as good as a cheap analog radio from the store.

The "FM2" portion of the schematic you're talking about with the parallel cap, vc and coil is apparently the entire tuning section of the circuit. The explanation claims everything else in the FM receiver helps amplify weak signals.