Gets more and more clear, or does it, PEP that is??
> Jim Thompson wrote:
>
> >Even old arrl ssb book (not handbook) sez peak is twice pep. Same goes
> >for light bulbs. 120v rms is really 170 V peak. 170v peak / fixed R =
> >peak I.
> >Peak I x peak V = peak watts. 100w light bulb =200w peak. Nuff said.
KH7M: Or, therefore........ 170v peak squared / R = peak watts ?
I have one of the "new" RF Applications VFD VSWR/wattcmeters.
Per the "technical discussion" in the accompanying pamphlet,
a "sharp attack, long decay" peak detector is used. To quote:
"RF power refers to the peak voltage measured on the line,
multiplied by itself, and divided by 50 (voltage squared divided
by the impedance of the load) which is watts." Which tracks,
I believe, with Jim Thompson's note above.
Does such a device read out an SSB signal's PEP power ?
I have noticed that using key down CW, I can get say, 400 watts
out of my solid state linear with just less than 50 watts drive
from the Omni VI+ transceiver. Powers as read on the
meter described above. 500 watt slug in my Bird 43
confirms pretty close to the VFD in this CW test. When
VFD reads 418, Bird reads 400 nearly exactly. Accuracy
of Bird is =/- 5 % of full scale reading, or in this case with
500 watt slug, Bird reading is supposed to be accurate
within +/- 25 watts, so guess the meters agree per their
spec ratings.
However, on SSB, the Omni output power must be increased
to about 80 watts, read on the VFD, voice peaks as indicated
by the flashing ALC light, to reach the same 400 watts
out from the linear on voice peaks. Unfortunately, the heavily
damped Bird meter can never get the needle above about
the 50 watt level during an SSB voice peak.
BTW, if I push the TUNE button on the Omni during the above
set up, that is for the SSB test, the linear puts out a constant
570 watts, and the Omni puts out 84 watts(VFD reading)
into the linear input terminal (though the Bird, with a 100 watt
slug installed reads out 90 watts).
The above notes may have nothing to do with the thread
discussion of "what is PEP"; however, I now have no
idea what my meter is reading when I set myself up
to see about 1500 watts indicating on the VFD at
what I presume are SSB "peaks" during a QSO. Per
the RF Applications manual, the meter is reading
a wattage equivalent calculation based upon the
value of voltage captured by a peak voltage detector --
is this the legal SSB PEP or something well below
the legal SSB PEP, which I gathered from one of
the thread posts, might in fact actually be 3 Kw??
Were my linear capable of doing so, would it then be
"legal" to operate with the VFD, as described above,
reading 3000 watts on voice peaks??
Just call me, for the moment a bit confused; or am I
like the King of Siam, "something's nearly so, others
nearly not!" What I thought was what, maybe is not.
I really think when the VFD reads 1500 watts on SSB
peaks, that reading IS indicating that my set up is
putting out the legal, Part 97 rules, limit. Am I
correct?
73, Jim, KH7M
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