Damping Higher Harmonics on a parallel LC-Oscillator? (1 port Low-, High-, Bandpasses?)
 

Hi,

I built a small FM Radio as shown on
http://members.aol.com/torkraemer/uk...ukwsender.html.
As it is it works pretty well, allthough I operate it without any
adition antenna.

Of course there are pretty high (unwanted) peaks in the frequency-band
at multiples of the operating frequency.
Because I don't want to use an additional antenna, I can't filter the
signal on its way from L1 to the antenna with a common "2-port
Bandpass".
Putting such a Bandpass (or Lowpass) between the DC-Source and the
LC-Circuit did not seem to work well.

So how can I damp those harmonics on L1 Coil? I thought of some kind
of frequency dependent impedance in parallel with the Coil.

I tried this with another LC-prallel Circuit which has an impedance of
approx. 0 Ohms at 200 Mhz. This works as expected but seems a bit
unsophisticated and the Impedance falls too slow as the frequency
approaches the 200Mhz.

Unfortunately I have no Idea how to design a "higher order
1-port-Bandpass", or even more likeably a Highpass.

What would you recommend?
What shoud I read?
Any suggestions are welcome.

Thanks to all, and sorry for the lenght of the message.

Diego S.