[BC] Freq agile AM transmitters

[Jim Tonne]

Willie:

Yes, just like the ham rigs, it looks like about 6 (maybe 7)
band would be needed.  Each band would be about 20%
in width.

So the transmitter would have to have 6 or 7 output
filters to get harmonics under control.

Nevertheless, this is quite a complication when compared
to a simple rig with no output tuning at all.

- JimT


----- Original Message ----- 
From: <WFIFeng at aol.com>
To: <broadcast at radiolists.net>
Sent: Tuesday, April 24, 2007 12:48 PM
Subject: Re: [BC] Freq agile AM transmitters


>
> 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...
>
>
>
>
>
>
>
>
>
>
> .
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