> Are there any thoughts as to the accuracy level in dBm in correlation > with this mod? As well as any sort of absolute accuracy specs on what > we expect to see with this box?
The absolute accuracy will almost certainly not be better than about +/- 2.0 dB... which is the best that spectrum analyzers from Rohde&Schwarz, Agilent, and others could do. Most people are quite surprised to hear that their US$70,000 spectrum analyzer could be off by 2.0 dB. But that is the reality. An error analysis of a spectrum analysis measurement is well-known: frequency response, mismatch, IF gain (reference level), and calibrator uncertainty all come into play. The result is somewhere in the neighborhood of +/- 1.8 dB or worse. That is considered quite good! When making a relative measurement (the difference between two signals) it's even worse. For more information and specific examples, see http://cp.literature.agilent.com/litweb/pdf/5968-3659E.pdf . The main thing to remember is that a panadaptor display is good, but it's not absolutely accurate in power. If you need excellent power accuracy, you must use a power meter. There are a lot of stages before the P3 panadaptor that conspire to increase the measurement uncertainty. Consider that before the signal even reaches the receiver it has already undergone the loss in the transmission line and the connectors. Do you know exactly how much loss you have in your transmission line and connectors? Following this, the signal then hits the receiver input which is not exactly 50 ohms. It could be 20. Or 90. Because it's not exactly 50, there is mismatch uncertainty. Already two errors right there. On the inside of the rx, there are a number of switches, cables, and bandpass filters (with amplitude ripple), then an attenuator and RF amp, mixer, and post-mixer amp. Take the attenuator for example. It might claim that its loss is -10 dB, but that's a nominal value that will actually be different for every K3. Each of the stages mentioned has an uncertainty in its gain, loss, or match which must be added to the total uncertainty. So these are all of the errors that add up to the figure I quoted at the outset. You might have better accuracy that this, but the point is you won't know if you do, so you must assume the worst case. Al W6LX ______________________________________________________________ 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
