In the 50's and 60's versions of the FCC Rules and probably earlier than that
there were references to having measuring devices" to measure the DC input to
the power amplifier final stage.
This was commonly interpreted as a plate volt meter and a plate current meter.
If both were available the legal input was to be limited to 1KW DC.
It was common practice years ago to only install a plate current meter due to
the cost and availability of meters when most, of not all, of the higher power
equipment was home built. If the plate volt meter was not installed, the plate
voltage was calculated from the transformer ratings and the type of filter
arrangement used. In the situation where the actual plate voltage was not
measured but derived the legal input power was limited to 900 watts DC.
All of these requirements (or limits) were removed when the FCC changed the
power limitations to the present 1500W Output PEP. I believe this was in the
early 80s.
When I was building power amplifiers for the particle accelerators I would have
the instrument calibrated by a NBS traceable lab. If I had 10 amps of RF
current into a 50 j0 circuit I was fairly confident that I had 5KW. This was a
relatively easy task because I knew, from direct measurement, what the complex
impedance was of the sources and the loads.
In amateur service I do not run the 1.5KW PEP because the amplifiers I have are
either single or two tube 3-500Z units or the Yaesu Quadra. None of which will
develop 1.5 KW.
I believe the FCC would expect some form of power measurement and would not
expect some elebrate scheme with NBS traceability under any situation.
If enforcement action was to begin for excessive power I believe the FCC may
make some field strength measurements, jst as broadcast stations are required
to do during their proof tests. Then the FCC may ask the amateur station to
operate at a given power level. If the given power level was 1.5KW from the
pair of under driven 4CW10000A tetrodes for example developed n near field at
1.5 KW and the other measurements by the FCC were 10 x n field it would be very
difficult to make anyone believe there was a descrepnetcy in the measurement
technique and the higher field strength readings.
In reality the actual power measurements are very difficult in amateur service
with better than a couple percent accuracy in any case, in most cases probably
it would be hard to better 20% accurarccy.
Does 1.5KW make a real difference above 1.0KW on the receiving end? Is this
difference decernable? Probably not.
During contests it is amazing how similar some of the QRP, LP and HP stations
have the same signal strengths. Must be the feed lines and antennas if the
power measurment techniques are similar.
Charley W1TE
In amateur service this is a bit more difficult because the complex impedences
vary with frequency. Even Bird truline instruments have inacuraccies with
varying impeadences.
>
>From: "Jim Reid" <kh7m@hsa-kauai.net>
To: <amps@contesting.com>
>Date: Wed, 26 Jul 2000 08:44:38 -1000
>To: <charley@net1plus.com>,
> <w8ji@contesting.com>
>CC: <amps@contesting.com>
>Subject: Re: Re: [AMPS] FCC certification - how do they do it?
>
>
>> Both of us have been amateur radio operators since the
>> 60's. I believe we realize the implementation of 97.315 and
>> 97.317 were not created to prevent licensed amateurs
>> from using full legal power (at the time 1KW if metering
>> was available or 900W if metering was not available).
>
>And how about "metering" accuracy? Quoting some
>words by Peter G3RZP a few days ago about accurate
>knowledge of our rig's output power at legal max.:
>
>"Hewlett-Packard rates their generators as +/-1dB the better
>ones, +/-1.5dB for the others. (Accuracy, NOT resolution).
>Now that is into an accurate 50ohm load. How low is the input
>return loss of the unit under test?
>
>If you are an approved type testing laboratory, your typical
>conducted power measurement to a 95% confidence level
>is +/-0.75dB. That's 1262 to 1782 watts. Such accuracy
>as this requires much better/more accurate power measurement
>than the HP spec.
>
> Do you have a friend at NIST who will calibrate a power
>meter at the 1500 watt level for you?
>
>Worrying, this measurement accuracy business, isn't it?"
>
>Will, pretty close to Peter's words, anyway, hi.
>
>73, Jim, KH7M
>
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