[Amps] Why are we building amps rather then transmitters? (Tubes vs. Solid State)

[Dan Mills]

On Fri, 2012-05-04 at 13:53 -0400, W2XJ wrote:

> What is being proposed is more like a legal limit flex radio. SDR goes a
> long way in helping to forestall obsolesce.

Probably fairer to say that SDR POTENTIALLY goes a long way in helping
to forstall obsolescence.
Without accepted standards for how to do this thing you would quickly
end up with lots of manufacturer specific boxes, with a really bad case
of connector conspiracy when it comes to plugging things together. 
 
It is not so much a legal limit flex, as it is a rethink about where the
exciter/amplifier split should most usefully be placed.
 .
Historically (in amateur use) this is always placed at a point running
medium power RF at the output frequency with the modulation already
applied (And this made good sense when RF generation was a pain and when
signal paths were almost entirely analogue (Preamp, mixer, filter,
mixer.... you know the drill) as most of this could be usefully shared
between the rx and tx paths. This also meant that an add on amplifier to
an existing radio was an obvious enhancement. 

I contend that with modern design the traditional feed the amp with the
radios rf output and a ptt relay is no longer the optimum approach, the
amp can now trivially contain its own processing and that means it is
better off getting baseband and frequency information rather then
something that you would apply to the grids/gates via a matching
network. 

This does of course make the 'amp' somewhat more complex, but frankly
small signal electronics these days is very, very reliable, and I don't
see this extra logic card significantly impacting on amplifier
reliability (PSU and thermal management problems seem to be the lions
share of the pain I see).

Regards, Dan