Jeff: It all depends on the power level you want the load to handle. Do you want to acquire now a dummy load that will handle the output of a KW amplifier in the future, or just the output of your K3?
If it's just the K3, then the MFJ-260C at $40 or so should be fine for 100W for extended periods at the calibration frequencies from 3.7 - 52 MHz. I burned up a much smaller MFJ unit that was an integrated PL-259 and a cylindrical heat sink that could handle 100 watts for very very short periods. During K3 Utility development I stopped the Tx Gain calibration code with a debugger with K3 key down for a bit too long and it Is No More. I don't find that unit in MFJ's catalog now, though. The Tx Gain calibration holds key down for a few seconds (maybe two to ten) on each HF band at 5 and 50 watts in quick succession. You might want to acquire a BNC to PL-259 adapter so that you can put your 50 ohm dummy load onto the XVTR OUT BNC connector for the milliwatt Tx Gain calibration step. That calibration really wants a 50 ohm load, although the power requirement is very small. For K3 Utility development when I run Tx Gain calibration over and over, I keep a Elecraft DL-1 on the XVTR out connector and an AEA DL-1500 (which is overkill) on the main rig ANT2 connector. 73 de Dick, K6KR -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jeff Hall, W6EZY Sent: Tuesday, February 23, 2010 10:14 AM To: [email protected] Subject: [Elecraft] Need to select a dummy load for K3 TX calibration...(advice?) Hello all, I need help picking out a proper dummy load to use for calibrating my new K3. HRO is just up the road and they carry some of the less expensive MFJ dummy loads -- would these be sufficient? Not looking to spend a lot of money, but don't want to buy junk either. What factors should I consider? I'm assuming oil-cooled dummy loads are more robust, while air-cooled loads are more compact, but you have to be more careful when operating or they can burn up more easily. The K3 manual says this is just a 5W test and I need a load with low VSWR from 160 to 6. What is considered "low" SWR? Anything under 1:5? If I can get by with the MFJ-260 for just $40, that sounds reasonable to me. 73 de Jeff, W6EZY ______________________________________________________________ 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
