I've been making tuner loss measurements for an upcoming QST review of some remote autotuners. My set-up is similar to the ARRL lab, but I've made a few changes. I have two different load boxes. One is a resistive load box that lets me measure loss with loads from 12-800 ohms. The second load box simulates different types of electrically short end-fed antennas - like a 43 footer on lower frequency bands, or an 8-footer like you might have mobile, and other combinations. I use Caddock thick-film 30-watt resistors for the resistive portion of both test boxes. For the short antenna simulator, I use series silver mica capacitors with shunt Caddock resistors.
Basically, I feed the 40 watt output of my test transceiver through a high power 6dB pad, through an Array Solutions PowerMaster, then to the tuner. So my test power is 10 watts. The 6dB pad helps keep the power relatively constant, but primarily ensures that any reflected power from a non-perfect tune (the tuners have a target of 1.5:1) is attenuated 12dB more if re-reflected by the transmitter. The output of the tuner feeds the load box. The load box has an output that feeds a 50 ohm attenuator/Minicircuits PWR-6GHS+ power sensor (that output is shunted or seriesed with Caddock resistors to give the required test impedance). So I start with no tuner in-line and adjust the Minicircuits offset so it and the PowerMaster read the same at 10 watts. They are both NIST-traceable cal'd, and were within 3% of each other, but I adjusted the offset so they are within 1%. Then I insert the autotuner, hit it with RF and let it tune. When tuning is complete I adjust the input drive so it is exactly 10 watts, read the output on the PWR-6GHS+, and compare that to the expected power under lossless conditions. Phil - AD5X ______________________________________________________________ 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
