[Motorola] AM from a Motorola ?

[Zapper]

Bruce wrote:

> Just a side thought, while I go through all this
> data I've rcvd on test sets, elements, boards, etc.
> And not that I would do this, but technically, is
> there a way to non-destructivly and reversably
> configure an FM Motorola (like a Micor VHF-lo, etc)
> to AM emission - perhaps by bypassing the FM Det/Mod ?
>
> I realize the output level would not be the same,
> but ...  -Can it be done- ?  The deviation of +-5kc
> would be about right for an AM signal width if it
> could be maintained at that value.  Should sound
> fairly nice if the PL filters that cut @ 300 hz
> were bypassed, and the 3kc was upped to about 5kc
> to add a bit of brilliance.
>
> Curiousity runs rampant here at times :)
>
> Plus I really enjoy listening to the 'Broadcast
> Quality' signals of the Gates (and other) stations
> on 3870 and 3880 KCs.
>
> Have a TMC SSB/DSB/ISB/AM/CW exciter that I hope to
> put on the air in the near future (after upgrade),
> but currently working on a couple vintage 6m/2m AM
> boatanchors that will probably be RF'ing first.
>
> Bruce
>
>    Corruptissima re publica plurimae leges...
>
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The question I have to pose is how are you going to modulate the carrier
in a linear fashion? One could modulate the inbound RF carrier to the
final amp or even modulate the B+ supply however most of these amps are
class C type output with maybe a 40-60% RF duty cycle. I suppose
modulating the inbound RF carrier would be the easiest however you would
need to figure out how to keep the amplification stages from going into
cutoff during the low points, this however may present you with a
nonlinear relationship to the outgoing signal. Another intresting idea
would be to modulate the last driven stage through the emitters and keep
a bias on the final output transistors however this would require a
large swing on the emitter current to get any linearity and trying to
keep the transistors from going into cutoff.

Gives good food for thought

Brad