[Boatanchors] Modern AM Modulation techniques

[Rob Atkinson]

Hi Jim,

I don't know much at all about Class D.  The component problems I have
heard of with the ham gear has to do with blown final FETs and I think
the problem is guys running the rigs into vswr loads that are too
high.  All of the class D rigs both ham and broadcast have to be on
antenna systems where the rig is seeing no more than 1.2:1 vswr.  The
broadcast rigs even have "antenna tuners" if I remember correctly.
they have high vswr alarms that trip off the rigs if there is any
excursion of line impedance.  I have heard all sorts of stories.
Some stations back when they first went solid state, had to have their
systems re-worked because they had towers with over 1.2:1 at the
bandwidth edges.  An AM bc station takes up at least 20 kc.  They'd
have a fine match at carrier frequency but trip off the rig when the
sidebands went out far enough to encounter the bandwidth limit of the
system.   The tube rigs didn't care.  I heard WSM in Nashville had a
problem with birds hitting their unbalanced open wire line and
tripping off the solid state rig when it was new.  The tube rig would
keep going and fry the bird.  They had to go to a buried pressurized
heliax line to solve the problem and keep the solid state rig happy.
The class E rigs supposedly don't have this problem but I don't know
anything about them.

There's about 2 or 3 months every year in summer when solid state has
minor appeal to me because the shack is just too dang hot for tubes,
so I operate CW or tend to other matters.  The rest of the time I'll
take filaments.

73

Rob
K5UJ

On Mon, Oct 5, 2015 at 11:56 AM,  <w5jo at brightok.net> wrote:
> Are those RF modules so expensive to preclude their use in Amateur
> equipment?   The commercial digital AM stuff for Amateur radio seems to have
> component problems and using those modules might take care of the problem.