[Noisebridge-discuss] Help needed to debug FM transmitter.

[Jake]

Hi Sriram,

I have a lot of experience with FM transmitters and i can tell you that 
the one you have is not going to make a good signal for you.  It's called 
a "free running oscillator" because it does not have a PLL to steer the 
frequency.

The idea is that you can "tune" it by hand to a particular frequency, and 
turn on a radio in the next room and hear yourself, and it's interesting 
and fun, but it won't stay on the same frequency for very long at all.

If you want to have a radio station that's on for more than a few minutes, 
and something powerful enough that it can be heard farther away than 
shouting, you need to get a PLL-based transmitter.  There are a zillion 
options on Aliexpress.com.  Many of them are total crap.

I suggest one with a BH1415F chip, between 5-15 watts output, and don't 
pay more than $100 including shipping.  Some of them have problems but 
most will work for you without any modification.  If you see one that 
looks good to you, email me the link and i'll tell you what i think.

what are you going to be using it for?

take care,
-jake

Sriram Srinivasan wrote:
Hello all,

I am new to electronics and I put together this FM transmitter kit from 
Jameco.
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_151239_-1

It doesn't work, and I would love to know why. I was wondering if someone 
can give the circuit a once-over, tell me about my soldering, and teach me 
about cool debugging methods.

I have a 100MHz oscilloscope (Rigol 1102e), and it seems like the 
transmitter is producing a carrier whose frequency seems to vary a fair 
bit (96-102 MHz). Given my oscilloscope knowledge, or lack thereof, I'm 
not sure if this is a problem for an oscilloscope that's working at the 
limits of its range.

Thanks much.

--sriram.