Question

Based on the circuit in the link below
http://circuit-zone.com/ediy_blog/724/simple-mp3-fm-transmitter.jpg

If I use a 7.3nF capacitor instead of the 10nF next to the 47k, use 10pF for the tuning, a 0.2uH inductor, 9nF capacitor for the 10nF next to the tuning, and 10pF instead of the 5pF under L1, what should be my output frequency in Hz?

Answer 1

The trimmer capacitor, the 1 - 30 pf is the key to what frequency you will be on, as it is adjustable. Let's use the .2 uH inductor, that circuit would then be resonant at the low end at 27 MHz and the high end at approximately 200 MHz (assuming the trimmer values is adjustable from 1 to 30 pF

With regards to the other changes specifically changing the 10 nF coupling capacitor to a smaller value, this will reduce your audio input from your iPod (source). In fact if I were to make any change at all, I would go to increasing the value of that coupling cap' as it seems pretty small for audio coupling.

The other changes you are suggesting is changing the amount of feed-back for the oscillator/output stage and as long as it oscillates and the output is sufficient then I guess your changes are O.K. Question: Why are you making these changes?