>> Power out on 12 and 17m is around 400W and 30m doesn't really work at
>> all. The reason for the low output, compared to all of you who
>> answered (most of you have over 1KW out), I don't know. Are the tubes
>> tired or do I have too little driving power. The IC-765 only delivers
>> 90-100W and that, I know, is not enough to drive 2x3-500Z to full
>> output. The output from the amp is anywhere from 600-900W depending on
>> band, 10-80M.
>
>The factory designed rating for the SB-220 is 1kW INPUT (~600w
>output) on CW and RTTY, and 2KW PEP on SSB (~1200 watts
>PEP out) on SSB.
>
>Good meters, like the Bird 43, have +-5% of full scale anywhere on
>the scale tolerance if they are within factory specs. Other meters
>are generally worse for tolerance. So a 2500w slug in a properly
>calibrated Bird 43 at 1000 watts true power could read between 875
>and 1175 watts. People often pretend Bird meters are 0%
>tolerance, but that is dreaming.
? Or wishful thinking. Furthermore, the accuracy of any RF wattmeter is
dependant on the measured resistance of the termination. If a wattmeter
is calibrated for 50? and the termination is 87?, the wattmeter will
provide a reading that has no basis in reality.
- A problem with many "1kW" Ham-type terminations is that they use a 50
- 75 watt rated resistor in cooling oil. At 1kW. the oil on the surface
of the resistor boils. Thus, contact with the cooling liquid is lost,
and as a result, the conductive film overheats in spots - so the
resistance changes. One way to discover this problem is with a DMM.
Going hammer-down at 1kW on a "1kW" Ham termination is looneytunes.
- Another problem with power measurement is that the Bird® 43 requires a
steady carrier, a.k.a., n0n (was called a-zero) . However, Ham type
amplifier anode supplies are rarely capable of n0n emission (the 3K-A is
an exception) since a 2500W CCS supply is required for 1500w out. With a
typical anode supply, anode-V drops under n0n, so a 43's watt reading is
not accurate on a typical amplifier. The only type of wattmeter that is
appropriate is a PEP type, if the amplifier is not driven with a steady
carrier. Bird® makes a fairly good one. The FCC uses it for station
inspections. However, my guess is that the FCC is aware of the vagaries
of RF power measurement, because I know someone in Frasier Park whose
amplifier measured c, 1800w PEP but he was not cited. Apparently, the
main thing is not to cause interference.
>I have a stack of calibration curves
>for slugs and meters I have to use, and that is with meters and
>slugs that are factory calibrated from time to time.
>
- Checking the accuracy of a PEP RF-wattmeter requires a Calibrated
oscilloscope, a calculator, a 100:1 or 1000:1 'scope probe, and a known
to be accurate termination.
P-pk=E-pk^2/R. P-pk/2=P-rms, which is PEP.
>You are really not that far off, and actually may be right on if your
>meter is reading on the low side. Measurements are always less
>than perfect, and RF power is one of the worst areas to measure.
Amen, Tom
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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