"RST Engineering" wrote in message:

The last bastion of VHF-AM is aircraft, both civilian and military. The
civilian aircraft com band goes from 118-137 MHz. and the military from
somewhere around 225 to 400. Those of us who have spent our lives in this
little corner of the design world are few and far between.

This is what I'm discovering. Not only are the people involved few and
far between but so is much of the documented background material
anyone new to the scene might rely on for help....8-( I hope some of
the old-timers will scribble some of this stuff down while they're still
around!

As for the "simplicity" theory - you've hit it spot on with your following
comments. For example, roll-your-own VCOs are only a few bucks
and pretty easy. Off-the-shelf Minicircuits types (e.g. POS-200) are
only a few bucks more. But it sure is interesting to note that Minicircuits
has a new line of VCOs *specifically* for "aircraft communications"
with an asking price of nearly $50 (yipes!)... The difference - VERY
low phase noise.

Apparently there are quite a few variables in implementation of these
"simple" designs - and what you can hear out there on the band is all
over the map. The difference in perceived quality between the "good"
radios and the really "rat-s**t" radios is amazing - and that's listening to
aircraft under identical conditions (for example over the same VOR
checkpoint). Sure leads me to believe that there isn't a set "formula" for
this stuff.......8-)

Bill

As to those who say that AM is so simple that anybody could do it, I
respectfully disagree. I even DISrespectfully disagree. Trying to
amplitude modulate a synthesized AM radio without having as much FM in the
output as AM is no mean feat. In the old vacuum tube days with crystals
for
the synthesizer it isn't all that difficult. However, with digital
synthesis and VCOs that will FM at the drop of a hat, it is far from
trivial. Shielding to the center of the earth and power supplies bypassed
from DC to daylight are the order of the day.

Jim


"Netgeek" wrote in message
...
Still looking for some pointers and/or advice on current AM
transmitter design. There doesn't seem to be much out there
apart from the "pirates" who are building SW transmitters
around 5W or so...(e.g. the "Grenade" QRP transmitters and
similar designs)...

Is AM ("Ancient Modulation") considered dead and therefore
there are no links/publications worth reading?

Bill