[AMRadio] AM Transmitter Advice??

Bob Bruhns bbruhns at erols.com
Sat Feb 18 20:54:02 EST 2006

Yep, I think it was a 6-month suspension, not a year as
I stated earlier.  (I plead slightly flakey memory.)

   Bacon, WA3WDR

----- Original Message ----- 
From: "Donald Chester" <k4kyv at hotmail.com>
To: <amradio at mailman.qth.net>
Sent: Saturday, February 18, 2006 8:45 PM
Subject: RE: [AMRadio] AM Transmitter Advice??

> John, WA5BXO wrote:
> >As I understand it the trick, that the FCC was to
prevent, and someone was
> >trying to get away with, was to run a 304TL with
about 100 Volts on the
> >plate in a GG configuration.  Forward bias it to a
high plate current like
> >1
> >Amp, so that it acts like a switch that is on.  Then
drive it with 5 KW
> >PEP.
> >It may have been some other some scenario as this
but I think you get the
> >picture.
> I had never heard of that, but it makes sense that
someone might try it.
> >     Then there was the trick that a gentleman up in
3 land, I think, was
> >going to run the high level double sideband reduced
carrier generator type
> >rig but he was not reducing the carrier just
increasing the SBs via an
> >extra
> >upside down tube, as it was commonly called.  The
sideband power would
> >continue to go up without distortion (if copied on a
proper synchronized
> >product detector) after the first tube was over
modulated in the negative
> >direction. The voltage and power would be diverted
to the upside down tube
> >where sideband power would continue.  There was
trouble with the specific
> >rule interpretation at the time in the FCC. Of
course any of us today,
> >would
> >be able to see that the upside down tube's audio
plate current and audio
> >voltage must also be counted as part of the input
power.  But the FCC was
> >having trouble deciding, at least as I understand
it.  At any rate, I think
> >they got him for being outside the 40 meter band
limits.  You may remember
> >more of the specifics on this Don.
> I knew the gentleman personally.  It was Fred, W3PHL,
near Phila, PA.  I met
> him at many hamfests, and visited him one weekend
back in about 1971.  I saw
> his rig, but by that time he had converted it to a
big SSB linear.  He liked
> to ragchew with VK's and ZL's in the pre-dawn hours
on 40m, using a 120 ft.
> high beam.  He not only fought the FCC, but had to
deal with a tower case as
> well (which he won).
> The loophole in the regulations was that the
definition of power was DC
> input to the final.  With the upside down tube
circuit, he ran about 600
> watts DC input, and then applied several kw of audio.
The rig was basically
> a high-level balanced modulator, but with DC applied
to one tube, which
> effectively unbalanced the modulation, he claimed it
was a plate-modulated
> AM rig, and that the legal power measurement was
limited to the DC input to
> the final.
> The signal was double-sideband reduced carrier, with
several kilowatts in
> the sidebands and less than 500 watts carrier power.
Althhough a
> synchronous dectector would have have taken full
advantage of both
> sidebands, most of the people he worked actually used
SSB receivers, and
> simply copied either USB or LSB, and used the carrier
only as a pilot
> carrier for setting the frequency on their receiver.
> The FCC couldn't make up its mind on how to  deal
with the issue, even
> though they could have cited a rule on the books that
limited modulation to
> 100%, and they could have said he was modulating over
100% in the positive
> direction, regardless of the fact that the signal was
clean.  Instead, they
> ended up citing him for splattering outside the 40m
band.  He liked to
> operate at 7290, and even though he had engineering
data to prove that his
> signal met all FCC specifications regarding spurious
sideband products, they
> said that the rules allow no detectable signal
whatever outside the limits
> of the amateur band, and he had detectable sideband
products above 7300,
> even though they might have been 50-60 dB down.
> I understand this whole thing was part of an ongoing
feud between Fred and a
> SSB group that was  competing for the frequency, and
the issue was brought
> up when the SSB group complained to the FCC.  They
suspended Fred's  licence
> for six months based on the citation for out-of-band
distortion products.
> The FCC referenced that case when they railroaded
through their p.e.p. power
> rule.
> Don K4KYV
> This message was typed using the DVORAK keyboard
layout.  Try it - you'll
> like it.
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