I'm not sure how to identify a trimmer properly. I heard it's marked with the first number as the lowest value in pF followed by the next two being the highest value. So, the picture below is 4-72pF? Is that true? If so, how about one that I have that says 103, is that 1-3pF? that seems unlikely, or is the zero like a multiplier, and it's 1-300pF?

PIC 1

I also need to make sure I know this is correct for variable capacitors like shown below. If I'm wrong can someone try in tell me the values of the capacitors in PIC 2
2.5 turns 48 - 59nH (Red)
3.5 turns 65 - 79nH (Orange)
4.5 turns 90 - 109nH (Yellow)
5.5 turns 109 - 132nH (Green)

PIC 2

Anyway, here's the project I'm working on that I think audioguru posted. I know it's simple but the last one I built took on a life of its own. I need to know if I could use something else for C5 that's suppose to use a 4.7pF. I have a 4 and 5pF on hand, and radioshack doesn't have anything in town. There's nothing for miles like that around here.

I need to learn more about capacitors, but I can't find any good (free) resources on the web. Can anyone tell me of a good site that will show me how to get a good hold on it.

Thanks for answering my noobie questions.

 

No, those are variable resistors not caps. You can see on the PCB silkscreen between them the label VR1. The 472 would be a 4.7K and the 103 a 10K trimmer pot. The resistance is in ohms and the first two digits are followed by the number of zeros specified by the last digit. 472 = 4700hm: 103 = 10,000hm:
Those are not capacitors. They are adjustable coils and may have a capacitor in parallel. Here's a link that describes some of the common ones:
http://hem.passagen.se/communication/ifcan.html
I would try a fixed 10-33pf cap and tune the circuit by spreading or compressing the turns on L1. You could also try a fixed 22pf cap in parallel with your 4.7pf trimmer, but you won't get much of a tuning range so you'll probably still need to fiddle with the coil.

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Wow lol, I was way. . . . way. . . off. I thought those were variable resistors until I read different online somewhere. I wondered why I could get an ohms measurement off them.

Well I proved myself stupid, my job here is done. Seriously though, thanks for posting a response and not just breezing over it. I'm sure it gets old answering the same noob questions all the time.

 

The simple FM transmitter circuit you posted has its antenna connected directly to its oscillator's tuned circuit. So its frequency will change when anything gets near or moves away from it.
It doesn't have a voltage regulator so its frequency will change as its battery voltage runs down.
It doesn't have a voltage regulator so the output level from its preamp transistor drops a lot when the battery voltage runs down. When the battery voltage is low then the sound is badly distorted.
It doesn't have pre-emphasis (treble boost) like FM radio stations have so the de-emphasis in an FM radio will cut the high frequencies and make it sound like your home stereo with its treble tone control turned all the way down.

Here is a simulation of the mic preamp transistor with a new 9V battery and when it has dropped to 6V.

Attached Images

sim-mic preamp.PNG (53.1 KB, 10 views)

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