Guy and all,
You are so correct. This is ham radio, and precision instrumentation
for power output levels is not the norm - a 20% error potential should
always be considered.
Yes, I personally have power instrumentation that is calibrated to the 5
% level up to 30 MHz. That level of precision has come at a goodly cost
and effort.
In general, amateur quality power measurement gear should be given a +/-
20% range of error. There are variations due to frequency, variations
due to changes in the dummy load actual impedance, and if one is using
an antenna, any common mode RF current can substantially influence the
readings on the meters.
In other words, what you see on your power meter may or may not reflect
reality. If there is any doubt about your results, tell me what your
results are when driving a known good 50 ohm non-reactive dummy load
(measure it with your antenna analyzer), and if a problem is indicated
with that load, then you can conclude that you have a transceiver
problem. If it is OK into that dummy load, but gives problems driving
your antenna, then you will have to solve the problem in your antenna field.
These are generalized statements and not directed at any particular
installation. If you and your indications are suspect, then investigate
your particular situation carefully (it is possible that we can help).
73,
Don W3FPR
On 2/7/2012 9:40 PM, Guy Olinger K2AV wrote:
> Hmmm,
>
> Given that ham-affordable components are full of minor and harmless
> frequency dependent characteristics, INCLUDING the antennas and dummy loads
> used, is there really any good reason to EXPECT 1.8-30 power output
> uniformity beyond what is commonly measured? Quite contrary to amps which
> were designed, built and certified to a broadband tight uniformity (and
> appropriately priced), if one WANTS exactly 500.0 watts from a KPA500 for
> some purpose, and you actually trust your output measuring instrument to
> deliver an accurate measurement to four figures, one just adjusts the
> drive, does one not?
>
> This is ham gear, not lab instruments, but I would be intrigued to hear
> what purpose this debated level of accuracy serves, other than light
> entertainment. I have sometimes heard some very interesting stuff coming
> from the other side of what I thought was the left field foul line. One
> never knows.
>
> ???
>
> 73, Guy.
>
> On Tue, Feb 7, 2012 at 3:23 PM,<n...@n5ge.com> wrote:
>
>> Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz?
>>
>> 73,
>> Tom
>> Amateur Radio Operator N5GE
>> ARRL Lifetime Member
>> QCWA Lifetime Member
>>
>> "Only the white eyes would believe they could cut the top
>> off a blanket, sew it to the bottom and have a longer
>> blanket."
>>
>> -- American Indian comment about Daylight Saving Time --
>>
>>
>> On Tue, 07 Feb 2012 13:35:47 +0000, Brian Alsop<als...@nc.rr.com> wrote:
>>
>>> Guys,
>>>
>>> I'm also curious about this-- especially what's going on on 15M.
>>> My values at 500 W out into a dummy load are:
>>> (amp), [volts], {efficiency}
>>> 1.8MHz DC (11.5) [63.1] {70}
>>> 3.5MHz (11.2) [63.5] {71}
>>> 7MHz (12.2) [62.5] {67}
>>> 10.1MHz (not measured)
>>> 14MHz (13.4)[61.8] {60}
>>> 18.1MHz (12.9)[62.8] (63}
>>> 21MHz (15.8)[61.2] {52}
>>> 24.9MHz (14.6) [60.1] {56}
>>> 29.7MHz (14.7)[60.4] {56}
>>>
>>> These are in reasonable agreement with David's except for perhaps 10M.
>>>
>>> The problem with these measurements are the wattmeter accuracy (10%?)
>>> and the current measurement inaccuracy. Default wattmeter calibration
>>> factors were used above. Elecraft is using a Hall effect device to
>>> measure PA current. It would be nice to know just what accuracy to
>>> expect from it.
>>>
>>> The efficiencies appear to be in the right ballpark. They tend to fall
>>> on a straight line log plot vs frequency, decreasing at higher freq's.
>>>
>>> If nothing else, the above numbers serve as a benchmark for future
>>> comparisons down the road for my amp.
>>>
>>> Note: The current measurement can be significantly affected by RF on the
>>> outside shield of the coax. Until a choke was employed on the feedline,
>>> the 24.9 MHz current with a real antenna measured 3 amps too low. With
>>> the choke it agreed with the above dummy load value. I suspect lots of
>>> KPA-500 users do have this condition-- given the types of
>>> antennas/tuners et al described by uses on this reflector.
>>>
>>> 73 de Brian/K3KO
>>>
>>>
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