XV-144 with high NF?
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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. Thanks in advance, Bob W1ICW -- Sooner or later, buying crap you don't need with money you don't have grinds to a halt." Jeff A. " "...the thought of owning a better piece of test equipment is usually sweeter than the reality of it." maynardb ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Bob DeVarney W1ICW
Actually, looking at the spec sheet for the ATF 34143 , I see that the
sweet spot for both NF and OIP3 seems to be around 40 mA current, so you would want 40 mA across the 4.7 ohm resistor = 188 mV.. so I'm not really worried about NOT getting the higher voltage but I am concerned about the high NF... -- Sooner or later, buying crap you don't need with money you don't have grinds to a halt." Jeff A. " "...the thought of owning a better piece of test equipment is usually sweeter than the reality of it." maynardb ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Don Wilhelm-4
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. > > 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. >> > > -- Light travels faster than the speed of sound, this is why some people tend to appear bright, until they decide to speak. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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