[BC] Freq agile AM transmitters

[WFIFeng@aol.com]

In a message dated 04/24/2007 12:10:49 PM Eastern Daylight Time, 
tonne at comcast.net writes:

> Willie:  How are you going to make a "frequency-agile"
>  output harmonic filter?   The kind where you "just set
>  the cutoff with a thumbwheel switch?"
>  
>  Making an oscillator move to a particular frequency is
>  a piece of cake.  Assuming the transmitter itself has
>  some harmonic content then an output lowpass or
>  bandpass will also be needed.  I am not sure that 
>  would be a piece of cake.

They do it in Ham rigs! :) Internal relays select the appropriate coils/caps 
to maintain spectral purity from 1.8MHz all the way to 29.7. That's ~16:1, 
which is quite a range. The same could be done with a MW box. The range is 
smaller, (~3:1) so even fewer "steps" would be needed to keep things in spec. A
 
simple microprocessor system would select the filter elements based upon the 
dialed frequency. Just like in the Ham rigs. The only real difference being MW 
has 
tighter standards on spectral purity. That same CPU could also report various 
status and sensor readings as well as accept commands via USB, serial, or 
Ethernet ports.

Willie...










 . 
**************************************
 See what's free at http://www.aol.com.