I can tell you from first hand testing of both a K3 and a K3S, in addition to
supply voltage, frequency, drive level, load Z and the phase of the moon all
effect TX IMD. DO NOT assume that just because you have the supply voltage at
the high end you are done. DO NOT assume that good IMD on 80-meters means good
IMD on 10-meters. ARRL should learn this.
For those with the equipment and inclination, some measurements might be
illuminating. The K3(S) makes it fairly easy since a two-tone generator is
built in. All that is needed is a spectrum analyzer to look at the output. I
happened to use an SDR-IQ and SpectraVue software, but even a second, carefully
calibrated and operated receiver will suffice. It will be laborious but
informative. (BTW, my measured data correlated within 1 dB, or less, to that
measured by Elecraft. You just have to know what you're doing.)
Wes N7WS
On 5/23/2016 12:42 AM, Bill Frantz wrote:
An addition to Jim's comments below.
All 100W rigs, regardless of manufacturer, whether the amp is part of the
radio or a separate unit, develop significant distortion as the voltage drops.
We noticed the effect at CQP last year. We were operating on batteries as our
hosts have a no generator rule. As our batteries got lower, our 3 stations --
2 K3s and a KX3 with KXPA100 -- started interfering with each other. The
problem went away when we replaced the batteries with fresh ones.
This distortion will also affect your signal as received by distant stations,
so it is undesirable in a rig unless you want a reputation for a bad signal.
One way to be able to get maximum runtime from your batteries is to use a
voltage booster regulator. I use a N8XJK Boost Regulator from TGE. This device
boosts the battery voltage to the radio. Mine shows 13.9 volts, receive and
13.4 volts key down at 100W on 160M, even with relatively low batteries. (It
does have a low voltage cut off to protect the batteries.)
The N8XJK Boost Regulator does generate some minor birdies on receive, so I
have it set up to only boost voltage when it senses RF output from the
transmitter.
73 Bill AE6JV
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