Mike, KT2E asked: How accurate have you found the internal power meter/wattmeter to be on the K2???
Reply: --------------------- Mine is well within the 1/2 watt at 5 watts as stated in the specifications. Measuring RF power at QRP levels is really not difficult. A low forward-voltage drop diode from the 'hot' side of the RF line to a capacitor that goes to ground will give you an accurate peak RF voltage across the cap. Measure that with a high-impedance meter like most DMMs today. RMS value is .707 times that reading. To get the power, multiply the RMS voltage times itself (square it) and divide the result by the resistance: 50 ohms. Actually, that's exactly the circuit the K2 uses to measure power. It gets a little tricker as you go up in power only because most diodes can't handle the voltages involved. One the places where many ops go "wrong" evaluating power meters is in the load. You *must* use a good 50 ohm load. An antenna tuner adjusted for an indicated SWR of 1:1 is not good enough. Not even an Elecraft ATU gives you a reliable load accurate enough for this. The mismatch presented by such a load can really throw off the power indications. That's because the SWR meters simply don't need a high order of accuracy. There's no useful difference between the efficiency of an antenna system or the rig when presented with an SWR of 1.2:1 or 1.3:1 compared to a true 1.0:1 match. Most SWR bridges are very vague below about 1.5:1. Yet these errors can really upset many power meters, including that used in the K2. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
