Bob, Armed with that information, you might want to re-visit the calibration data for your NF measurement equipment - the two measurements do not support each other.
73, Don W3FPR On 12/5/2010 9:14 PM, Bob DeVarney W1ICW wrote: > I guess I'm not going to worry too much about it. > > I just did a MDS measurement with my HP Service Monitor. MDS was > around -157 dBm in 400 HZ bandwidth. Preamp on, AGC off. My HP 8921 > only goes down to -137 dBm do I added a 20 dB pad in line to get down > to -157 dBm. Still barely audible in the headphones at that level. > I set the rf preamp bias to 40 mA=188 mV at TP2, and tweaked C1 for > best S/N at -157 dBm and I think I'll call it good. > > Thanks for the sanity check, Don. > > I've been trying to find a culprit for missing a couple juicy EME > dxpeditions lately, but I guess I can't blame it on the receiver just > yet. > > 73, > Bob W1ICW > > On 12/5/2010 7:50 PM, Don Wilhelm wrote: >> Bob, >> >> I do not have calibrated Noise Figure measurement tools, so I do a >> quick assessment of the XV transverters using the calibrated >> attenuator output of my HP8640B signal generator, which will go down >> to -140 dBm. I view the K2 output on Spectrogram and use a 400 Hz >> bandwidth. With a properly functioning XV144, I normally can see the >> signal at 10 dB or more above the receiver noise floor. >> >> MDS = -174 +10(log Bandwidth) + NF + SNR >> >> If I assume the SNR is zero (yes that will give the worst case NF) >> The 10(log Bandwidth) value is 26 dB for a 400 Hz bandwidth >> The implied MDS of a signal seen 10 dB above the noise floor is -147 dBm >> That measurement further implies a NF of less than 1 dB, which is >> within specification. >> >> I would suggest you do a similar MDS measurement as a quick sanity >> check on your NF measurements. >> > ______________________________________________________________ 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
