Just a comment on dummy loads: I do a lot of ham radio work at VHF and higher (up to 10-GHz), so making good power measurements involves having a good 50-ohm termination (load). For most of my testing I have several coaxial loads: A 25w Termaline (Bird) is used a lot in the shack as it tests Z=51 + j0 on my MFJ-269B antenna analyzer and shows zero reflected on a Bird43 power meter. Some of the other loads show 52 or even 54 ohms on the MFJ, and not quite resistive (I marked all them so I would know). In all cases resistance measurement with an ohmmeter agrees with the R parameter in the complex impedance equation.
I even have a 500w Sierra termination (door stop load) which has a integral power meter, but it is not exactly 50-ohms and the meter is not in agreement with the Bird43, so I use it as a safe load for high power but not for high accuracy measurements. I have seen coax loads shift way off 50-ohms due to overheating from too much or too long a transmission. I bought some of the Cadsoft 100w surface-mount attenuators to use in a 900-MHz amplifier to permit driving with 10w exciter. They were in the $12 range from Mouser. One can make very fine 50-ohm loads using them on a proper heat sink at a fraction of the cost of coaxial loads. 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? DUBUS Magazine USA Rep [email protected] ====================================== ______________________________________________________________ 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
