As part of a detailed series of transmitter performance measurements (still underway), I measured my K3's current requirements at various supply voltages and output powers for all bands.
At 100 watts commanded power, tune mode, and with 13.8 V nominal applied (13.797 measured), I measured the following current requirements: Frequency (KHZ) Current (A) 1850 17.919 3900 17.116 5330.5 17.094 7250 16.796 10120 18.544 14175 18.587 18120 15.232 21250 16.966 24950 15.53 28350 14.308 The power supply used for these tests is an Hewlett Packard digitally controlled model 6652A with remote voltage sensing--the sensing leads are connected to the Anderson connector where it enters my K3. Hence the wiring drop (but not the connector drop) is compensated for. I measured the standard Elecraft 5 ft cable as having around 40 milliohms loop resistance, if I remember correctly, which amounts to 0.72 V drop at 18A. My notes are in the basement and I'm writing this from a couple of floors above, so I could be mis-remembering the number slightly. The figures are shown in three decimal places, as that's how the HP 6652A reports. The instrument's stated accuracy is +/- 0.15% + 26 mA. In addition to the band-to-band changes, reflecting different efficiency, my data shows that the current requirement is more or less independent of supply voltage, with only a small change in current noted for a particular power output as the supply voltage changes between 11.2V to 15.0V. I assume this is because the majority of the supply current goes to the HPA stage and the final transistors have more or less constant base drive so the finals operate in constant current mode with respect to the DC supply voltage. This has some interesting ramifications for efficiency and heat dissipation versus supply voltage when one is operating CW, more about which when I complete my measurements and finish writing up the analysis. Jack K8ZOA www.cliftonlaboratories.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
