I am confused. The circuit on the link you provided shows an antenna. You
need to get some sort of low pass characteristic between your transmitter
and the antenna. That is what I was trying to suggest. Perhaps a
capacitive tap feed to the ant instead of the inductive tap. Again, with
only the osc, this is not easy:


Original ckt
+V
|
|------------0
|-----| Ant
|/ C
= O----------0
/|C6 I
| L L1
|-----|
|
|/ Collector
B-| TR1
|\ Emitter
*****************************************

+V
| New circuit
|
|--------|-------------------0
C = Ca ant
O L1 |--------COIL--|----0
I |/ L2 |
L = C6 =Cb - Low pass pi net
| /| |
|--------| gnd
|
|/ Collector
B-| TR1
|\ Emitter

I estimate Ca & Cb to be approx 100-150 pf. L2 resonates with (1/2)*(Ca
series Cb)

If you are not using an antenna and just radiating from the circuit, then
your only hope is to either box it up or reduce the TR1 current to reduce
the harmonis content (increase R1... 200, 500, 1000, 2000,...)

Steve



"kb" wrote in message
...
Thanks,
but i dont want to use an antenna. Or did you mean the dc-input of the
LC-transistor-oscillator by "antenna"?


On Mon, 16 Feb 2004 16:08:15 -0600
"Steve Nosko" wrote:

An idea:
Use shunt feed and a pi network. It is a low pass filter. Since TR1 is
also the oscillator, you may need to add an amplifier.

+V
Choke
|
|-------Coil---- ANT
| | |
| = =
| | |
| gnd gnd
|
|
|
|/ Collector of TR1
B-|
|\ Emitter




"Diego Stutzer" wrote in message
om...
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.