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: [email protected] [mailto:[email protected]] 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
