FM Transmitter Construction

For all the discussions about FM transmitters lately, and SMT construction techniques, here's a picture that shows the technique I've been blathering about. The transmitter that is copper colored has a solid ground plane. The other one doesn't because it's actually cut into the ground plane of a scrap PCB.

j.

Hi John. I downloaded that thing on grounding. Does a ground plane mean u just connect copper on the top of the board to ground? How long is your antenna? And how far does it transmit (Are you using a sensitive radio or a piece of junk)?

Thanx :lol:

John Sorensen said:

For all the discussions about FM transmitters lately, and SMT construction techniques, here's a picture that shows the technique I've been blathering about. The transmitter that is copper colored has a solid ground plane. The other one doesn't because it's actually cut into the ground plane of a scrap PCB.

j.

Click to expand...

Nice work. Those look good.

Does a ground plane mean u just connect copper on the top of the board to ground? How long is your antenna? And how far does it transmit (Are you using a sensitive radio or a piece of junk)?

Click to expand...

A ground plane is just a solid plane of copper. Returns (grounds, commons) connect to the plane instead of having a distinct path to the common. That allows the currents to flow along the path of least impedence, reducing emissions and susceptibility (and other benefits like easier routing, distributed capacitance).

The antennas are pretty short, like a foot maybe. The length of the antenna affects tuning, too. So, for the one without the tuning cap (the one on the bottom) I might trim a little here and there to put it closer to a frequency I like. I never really tested the range because I just wanted it to work within the house, and it does. I mean, when you say range, what does that really mean? Line-of-sight or with obstacles? What kind of obstacles? Etc.

I find the junkier radios work best for these transmitters.

j.