Re: More on PEP, AM, average power, etc.

Are you as dumb as you seem??

--

Clif
"Straydog" <asd@xxxxxxxxx> wrote in message
news:Pine.NEB.4.63.0601252142230.9221@xxxxxxxxxxxxxxxxxxx
>
> Since my earlier post (dealing with the question of what is peak evelope
> power output in an AM transmitter), I've been doing more scrutinizing of
> tube Ip/Vp characteristic curves. They are much more non-linear than the
> impression you get from just looking at the curves. Also, it is rare or
> almost non-existant to find Ip vs screen voltage!
>
> Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
> manual). This is a KW input class C triode.
>
> From the curve:
> at zero grid volts, 1 kV on the plate gives 175 ma plate current
> 2 kV 500 ma
> That's more than a doubling of Ip for a doubling of Vp
>
> at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
> 4 kV 750 ma
>
> looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
> a sharp cutoff tetrode that only at zero grid volts was there a near
> linear relationship between plate current and plate voltage (meaning zero
> current at zero voltage, and a straight line [which actually deviated
> slightly from a straight line] with some slope. But at 100 v on plate,
> current was 14 milliamps, at 200 v on the plate, plate current was 34
> miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode, and
> at any of a wide range of grid voltages, plate current could be
> doubled with only a 15-20% increase in plate voltage.
>
> My thinking on all of this leads me to claim that anyone who can start
> with a 100 watt carrier from an AM transmitter and make a few assumptions
> about 100% modulation and come up with a _calculation_ of something like
> 400 watts of peak power and represent that as having something to do with
> reality is pure conjecture.
>
> If anyone wants to put an appropriate oscilloscope on the transmitter
> output
> and measure the RF voltage of unmodulated carrier into an appropriate load
> and then measure the peak RF voltage when the carrier is modulated, then
> and only then do they have a reasonable _basis_ for making a claim about
> peak (instantaneous) output power.
>


.

Relevant Pages

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