On Wed,12/28/2016 6:59 PM, Paul Baldock wrote:
What gives you the impression that SPE chose to ignore it? All of
their amplifiers shipped to the US have attenuators that limit the
gain to 14.5dB.
Not quite true. I don't know the history of the distribution of SPE amps
in NA, but just measured (with a factory-calibrated LP-100A wattmeter)
16.5 dB gain for the SPE 1K-FA that I bought from my neighbor, W6GJB.
The measurement was on 20M CW, and I measured both the drive level and
the amp output at the amplifier output. Glen bought this amp about 3
years ago, and it is unmodified. I measured with 10W drive and about 24W
needed to get the amp to start reducing input gain. The gain was
essentially the same below about 950W output; above that, the amp
reduced input gain a few dB. The amp reports its gain on the front
panel, and those indicated gains corresponded to my measurements.
Measurements were made working into my SteppIR, with its frequency set
almost exactly to the operating frequency.
The IMD from this amp is significantly higher than my "good" amps, so
I'll eventually replace it, because I can't use it for contesting
(because the IMD makes it broad on CW). The Titan remains my contesting
amp, clean as the K3 that drives it at legal limit. But the SPE gives me
3 dB more than my KPA500 on 6M (and instant on at HF), which is why it's
on my operating desk. :)
My 87A measures 14 dB gain with about 5W drive on 80 CW. I didn't look
at higher power levels. I haven't measured gain of the Titan, but I'd
guess it's pretty close to 15 dB based on interpolating other measurements.
Potential source of small errors for all measurements is that the load
that the input network for these amps place on the K3 is unknown. The
SPE antenna tuner is in place with the amp both in and out of idle mode,
so the K3 is driving at matched load when the amp is is in idle. The
output networks of the 87A and the Titan are bypassed when the amps are
in idle, so the K3 is driving the antenna. My guess is that the error is
no more than 0.5 dB, but it is a guess.
Glen says the 1.3K he bought is close to 14-15 dB gain, but that the
vendor offered to tell him how to get the additional available gain. It
would, indeed, be nice if SPE used the additional gain to reduce IMD.
But the DXpeditioners love the 1.3K-FA -- it's light weight (thanks to
an SMPS), very close to legal limit. And when you're DX in the middle of
nowhere, you don't have neighbors who care if you're a bit broad. :)
73, Jim K9YC
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