I'm designing an APRS tracker using a clock chip as the signal source. This works well, except the carrier signal (144.39MHz) is a square wave, not a sine. An LC low pass filter cleans that up nicely. The signal, however, needs to be amplified, and I'm not sure of the exact way to "process" the output.
I'd like to use some sort of MMIC amplifer to take it from the current output level of about 25mW to somewhere in the 100-500mW range.
So the question is where the filters should go. I can see at least three options:
1) source -> amp -> filter -> antenna
2) source -> filter -> amp -> filter -> antenna
3) source -> filter -> amp -> antenna
I have always learned that a low pass filter is required on the output of any amplifer, to block any spurs generated by the amp. This would tend to rule out #3.
But I'm wondering if I should have any sort of filter between the signal source and the amplifier itself. Is that better than amplifying all the odd harmonics only to need to filter them back out? I'd prefer to avoid the extra components involved with a second filter if I can, but not sure what's best practice here.
Thanks.