Hi Doug , et al:
At 08:08 09/23/2007, DOUGLAS ZWIEBEL wrote:
The posted assembly manual suggests the use of an "RF 50-ohm dummy
load with low VSWR across the range of 160 meters through 6 meters."
Later, under the TRANSMITTER section, "Connect a dummy load capable of
dissipating 5 watts to the ANT1 output."
Which begs the question (at least for me): Will we need a 100w dummy
load when installing the KPA3 or will the "low power" dummy be
sufficient?
Good question... here's my take on a response...
IF you only have the QRP K3, then a low power dummy load (though I'd want
it to be able to handle 15W continuously (for other testing scenarios)
should be quite adequate. I'd also want it to be of good enough design
that it presents not only 50 Ohms, but 50-Ohms RESISTIVE... e.g. low or
no reactances across the bands of interest.
However, if you have a K3-100 (with KPA3), there are some tests, and
possible set-up scenarios where you will be required to transmit into a
50-Ohm (resistive) load at the 50W level for a very short period of time
(say 3-5 seconds) on each band. This is part of the procedure which allows
the K3 to pre-set its drive levels (at the 5W and 50W levels) for each
band, so you don't have to worry about adjusting your drive (the ALC
adjustment) while operating and switching from band to band.
Were it me, I'd opt for a good quality 100W (or so) dummy load and be done
with it. There was a thread here a few months ago about some commercial
(Celwave) dummy loads which were being offered at extremely attractive
prices (https://www.ridgeequipment.com/store/dummyloads.html). I have the
200W, 75W, and the Celwave 15W loads which they show there and they work
great... and they really ARE flat up to well into the GHz range. And the
prices cannot be beat. I have NO 'interest' in Ridge Equipment, other than
that they offer some nice dummy loads.
73,
Tom N0SS
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