David, The DL-1 wattmeter is likely quite accurate. If you are using a slow DVM, be certain that you allow enough time for the readings to settle down.
The formula in the DL1 manual should be correct with the exception of the diode drop (the 0.15 constant in the voltage could vary a bit from diode to diode). Remember that the diode detector reads peak voltage, but only across half of the load. If the RF voltage is 2 volts or higher, the diode drop becomes insignificant - 0.15 volts divided by 2 volts is 0.075 meaning less than a 7.5 percent error if the diode drop is ignored. This error becomes less as the voltage reading increases. It is quite possible that your particular diode has a lower voltage drop than the formula's 1.5 volt average drop. The diode drop and the actual value of the dummy load resistance should be the only quantities that would vary in the formula. The accuracy will be directly proportional to the actual resistance, and the actual power will be dependent on the square of the voltage, so the voltage is the most significant factor. I will have to give it some more thought, but I believe the formula may be better stated as; ((V+1.5)SQRT2)^2/50 because the diode drop should modify the peak voltage rather than the RMS, but I will have to give it some study to be sure (I could be wrong and it is late at night). As I said, if your voltage readings are in excess of 2 volts (about 0.05 watts), the diode drop becomes less and less significant as the measured voltage increases, so only at QRPp levels is the diode drop a significant factor. Drawing conclusions for a difference of less than 10% is risky and can have other variables involved such as the actual resistance ot the dummy load - the resistors are 5% tolerance and can account for a part of the discrepancies that you are seeing. Measuring the dummy load with an antenna analyzer can be informative. 73, Don W3FPR > -----Original Message----- > > 3) How accurate is the DL-1? Does it tend to read hi (optamistic) or lo > > (pessamistic)? > > I asked this because the the KXAT1 reads higher than the > calculation I get from > the DL-1. The DL-1 matches the KXAT1 if I use the following calculation > (instead of the one supplied in the DL-1 manual): > > P=(((E*sqrt(2))+0.75)^2)/50 > > Of course, this could be miscallibration of my volt meter. > > _______________________________________________ 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
