[Elecraft] Dummy load for KPA3?

[Dick Dievendorff]

I have acquired a number of dummy loads over the years.

A lot depends on your ultimate needs.  If you buy the minimum now, you might
end up buying something larger later.

For the purposes of K3/100 Tx Gain Calibration, you'll need a dummy load
that can dissipate 50 watts for short periods.  Tx Gain calibration holds
the key down on each of 6 frequencies at the 5 and 50 watt power levels for
about 4-10 seconds at a time.  

If you're careful, that can be handled by something as small as an MFJ-261
that is rated for 30 watts or 100 watts "peak".  I burned mine up while
testing Tx Gain Calibration when I stepped through the code with a debugger
and left the transmitter on for too long.  I didn't replace it. It's a very
convenient size.

I recently bought a pair of 75 watt dummy loads from Ridge Equipment. I'm
using them for an antenna tuner project where I want the load to be really
just resistive on all interesting frequencies. They come with N connectors,
so you might need an SO-239 adapter that Ridge Equipment also sells.  I like
these very much.  They are "like new", and present an SWR < 1.02 up to about
700 MHz.  At 3 GHz they get all the way up to 1.12.
https://www.ridgeequipment.com/store/dummyloads.html

If you eventually expect to use an amplifier, perhaps a higher power dummy
load would be a good investment.  

A "dry" dummy load like an AEA-1500 or Palstar DL-1500 can handle 100 watts
for extended periods (10 minutes or so) or 1500 watts for a few (10)
seconds.

If you need to support key down at full 1500 watt power for a few minutes,
you might want a can filled with mineral oil, such as the old Heath Cantenna
or Ameritron ADL-2500 or MFJ -2500.

If you're testing high power amplifiers for extended periods, you might need
to invest in something with a fan, such as the Palstar DL2K, DL5K, Ameritron
ADL-2500 or MFJ-265.  The high end of these is the Alpha 2100, which
reportedly handles 1500 watts indefinitely.  It is what RF Concepts calls a
"legacy" product, however.

I normally think of a dummy load as something I'd use primarily in testing
and calibration, but I've recently thought of a good use for it in a contest
multi-radio antenna switching project when I need an "antenna" to switch an
exciter to during band transitions.  I don't want to leave the antenna
connection open or shorted while I switch a radio to a band where another
nearby radio could be transmitting, so a low power dummy load is just a
perfect "antenna" for this. The receiver is somewhat protected from "same
band" transmitters, and if the exciter is keyed it won't see a load that
exercises the transceiver's protection circuitry.  

73 de Dick, K6KR






-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Miller
Sent: Tuesday, February 07, 2012 7:11 AM
To: Elecraft Reflector
Subject: [Elecraft] Dummy load for KPA3?

I'm considering adding the amp to my k3/10. I see a 50w dummy load is reqd
for setup. Any recommendations? Should I get a 100w one instead?

Build vs buy?

73

jim ab3cv
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html