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. If it is as bad as you indicate, you may have a bad preamp in that XV144. Your RF Amplifier Bias adjustment is not unusual - 175 mV is the minimum, but it usually maxes out in the 210 to 230 mV range - I have not yet seen one that would go as high as 275 mV. 73, Don W3FPR On 12/5/2010 6:36 PM, Bob DeVarney W1ICW wrote: > I an wondering if anyone has encountered this before. > I have a recently built ( this spring ) XV-144 external transverter > teamed up with my elderly K2. The K2 was updated to all the most recent > mods, builders alerts, and firmware upgrades as of mid April. > The transverter has a high noise figure in the neighborhood of 10 dB > when measured with a known ENR noise source and either the VK1OD of > G8KBB noise figure software. > I have also measured the transverter using my Kenwood TS-2000 as an IF > rig and have similar results. > > Before I yank the covers off and get out the magnifying glass, can > anyone point me in a good direction? > > I set C1 for a noise peak at 145 MHz per the manual, but the RF amp bias > would not go above 220 mV at TP 2 so I suspect something in that area. > ______________________________________________________________ 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
