[AMRadio] AM Linear Operation

Jim Candela jcandela at prodigy.net
Sat Mar 18 10:37:19 EST 2006


    It might be doable to use a watt meter that either
looks at RMS carrier power, and PEP power by the flick
of a switch. Since on AM the PEP at 100% plus
modulation is ideally 4 times carrier power, the watt
meter will show that, say for a 100 watt carrier, you
should get 400 watts PEP.

    If you have a watt meter that can work this way
and communicate to you by talking, tones, or whatever,
then setting a linear amplifier up into a dummy load
is doable. Just advance the RF drive until the four to
one ratio drops, and then back off the drive a little
from there. If you can follow this approach you will
have a linear amp running AM set up better than many

   You will need to juggle the mic gain, drive level,
and linear loading to see how much carrier you can
transmit while preserving the 1 to 4 ratio, and do so
without the visual aid of a scope. This will take some
   Once everything is set, then your antenna must
appear identical to your dummy load, or the linear
plate & loading controls must be readjusted. If this
is the case leave the mic gain and drive alone for
this final step. Making the antenna appear the same as
the dummy load sure simplifies things, and a tuner may
be helpful.


--- "Mike Duke, K5XU" <k5xu at jam.rr.com> wrote:

> I've been reading this AM linear thread with great
> interest.
> I currently run a TS570 which gives me no more than
> 25 watts of carrier, 
> plus a bit more on modulation peaks. I have an
> unmodified DX60 that I intend 
> to put back in service later this summer after a
> shack painting project is 
> finished. (No need to move it twice!)
> Because I enjoy operating, and would like to do so
> with enough signal to be 
> heard reasonably well on 80 and 40 meters, I too
> have been considering which 
> linear to run on AM.
> This discussion of linears on AM has caused me to
> reason that there is no 
> exact magic combination of carrier drive level and
> audio level which is 
> guaranteed to produce a cleanly amplified AM signal.
> For me, at least, this 
> apparent fact is most unfortunate indeed. My
> signature will give you a hint 
> of the usefulness of a scope in my shack.
> So, do I sit on my hands and wait for better
> propogation on the higher 
> bands, or do I continue serving as the pin-drop test
> for all those restored 
> 75A4's, HQ170's etc?
> Mike Duke, K5XU
> American Council of Blind Radio Amateurs
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