[AMRadio] Power Levels

[Bob Bruhns]

Two errors.  The US amateur regulations limit us to 1500W
PEP output (not input).  If your output is 400W carrier and
you have 100% modulation, you have 1600W PEP, not 2000W PEP.
And the 400W carrier output is pretty optimistic if you're
running 500W input; it assumes 80% efficiency.   Typical
efficiency of class-C RF amplifiers is 75%, which would give
you 375W carrier output with 500W input.  At 100%
modulation, that comes to 1500W PEP.

So the AM community has come up with the approximate rule of
500W carrier input, and 375W carrier output, 100% modulated.
But the regulations actually say 1500W PEP output power, not
500W DC input or 375W carrier output.

The FCC has said they would be interested in the size of the
transmitter tubes and output tuning section. They are not
too concerned that that someone with a pair of 813's COULD
be running illegal AM power, because the extent of the
violation would only be 2 or 3 dB.  However, they would not
be inclined to accept excuses from someone with 480V 3-phase
power feeding a transmitter using a 4CX10000 modulated by a
pair of 3CX10000s, or from a California-Kilowatt SSB
operator with three 3CX10000s in parallel.

However, when the FCC has someone on their radar screen and
the order is to seek and destroy, you can bet that they will
raise any overpower issue they can.  So the guy who does
broadcasts every Sunday night and accuses the FCC of being
traitors who should be tried and hanged, while remarking
that he is using a Johnson desk-KW at full power plus, will
be one of the first ones to receive such a citation.  If the
other Sunday night broadcaster runs full power on his KW-1
while running unattended broadcasts with a Radio Shack
timer, he will also be among the first cited.

  Bacon, WA3WDR


rbethman at comcast.net wrote:
>
> Al,
>
>     There is no need to apologize.  Especially for the
anal retentive
> individuals.  I do not have Part 97 in front of me.  I do
believe that the
> segment covering power levels is quite clear.  It is
supposed to be 1500W
> PEP IN to the PA.  There is then the reduction in the
output in the percent
> efficiency department.
>
>     If your OUTPUT is a 400W unmodulated carrier, then
modulated at 100%,
> then the PEP of the output is clearly illegal.  The reason
is that 100%
> modulation is four times the carrier.  Hence a 2000W
output.  This would be
> a phenomenal occurrences since there would be more output
than there would
> be input.
>
>     The is a LOT of don't ask - don't tell going on
amongst the AM
> community.
>
>     I guarantee you that those running T-368s and BC-610s
that are properly
> tuned ARE running illegal.  Then there are those that goes
steps farther.
> There are a few that run in the neighborhood of 10KW
output, and some that
> are running just a few KW.
>
>     Don't let the anal retentive individuals drive you
off.
>
>     1) THEY are not the list moderators or list police.
>
>     2) You ARE asking a very valid question, and seeking
knowledge.
>
>     3) We all strive to learn, run good clean stations,
and be good Amateur
> Radio operators.
>
>     Go with peace and ignore those that refuse to broach
topics that make
> them uncomfortable.
>
> Bob - N0DGN
>
> Bob - N0DGN  Craf-T-Bob  (Because I love Hallicrafters!)
> Apache(2), Mohawk(2), HT-32A, SX-99, SX-101 mk III, R-390A
> EAC, R-390A Collins, DX-60 w/HG-10, BC-610I, BC-939A
>
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