I agree. A complete transmitter would solve many technical issues and
depending on the implementation, could drastically improve performance.
Solid State broadcast transmitters that transmit digital carriers along
with analog and therefore must run in linear mode can achieve IMD under
-80 DBC using techniques most easily implemented in a composite unit.
For an I/Q interface, I think SDR has evolved to the point that Ethernet
is all that is required. Any control or tuning can use the same Ethernet
connection.
On 5/3/12 4:37 PM, Dan Mills wrote:
> This whole topic has got me thinking....
>
> Given that small signal RF generation is pretty much a non issue these
> days, I have to ask why build amps intended to take a modulated RF
> signal at significant power as the input at all?
> Doing this makes a lot of really neat and highly efficient architectures
> essentially impossible to implement cleanly and does not really save
> much circuitry.
>
> Would it not instead be better to have the radio output an I/Q pair at
> baseband (Possibly as spdif or something) and simply tell the 'amp' what
> the carrier frequency should be over CAN or RS485 or something?
>
> This way the 'AMP' can play all sorts of EER/Class E/dynamic bias/
> whatever type games and can implement ALC that actually works properly,
> resulting is very much improved efficiency, and the overall chain
> becomes simpler as the front end does not need (redundant) output
> filters or in fact any significant heat generating parts.
>
> Further, something like this could (because RF power is not being moved
> from the exciter to the external PA) allow the link to be a simple
> ethernet cable or such, making placement of the TX box close to the
> feedpoint trivial.
>
> There might be something to be said for building transmitters instead of
> amplifiers.....
>
> Regards, Dan.
>
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