K3 Sensitivity
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I assembled my K3/100 with the second receiver in December of 2010. The
weak signal performance was much better than my original IC-756 rig. I did not install the automatic antenna tuner. I have continued to download the software changes since then. Two years ago I installed the general coverage receiver modification. I thought it was my imagination at the time but I thought had experienced a slight decrease in the primary and secondary receiver sensitivity. Today I put my Kenwood TS-480 that I had been using as a mobile in the shack. I was listing to a couple of weak strength SSB QSOs using the K3. Out of curiosity I switched over to the TS-480 and was surprised that the weak signals were more "copy-able" on the inexpensive Kenwood than on the K3. Does this indicate a problem with the RX in the K3 or is the apparent difference in the TS-480 RF gain come at the price of the definitely poorer adjacent signal rejection? ______________________________________________________________ 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 Message delivered to [hidden email] |
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Jay,
As promised, I went ahead and measured my K3 sensitivity. It is really a K3S-. It doesn't have the USB I/O board but has the rest of the K3 -> K3S upgrades. There general coverage bandpass filter board is installed. Here are the results on 20-6M. The sensitivities are as expected and comparable to other rigs' published results. They also seem to agree reasonably well with more well equipped lab K3 results. I don't claim well equipped lab accuracy. Condx: 1) SubRX off, attenuator off 2) CW mode 3) 400 Hz filter in 4) Measured the S/N with Spectrogram. These numbers are based upon a 10 db S/N ratio. That also happens to be the MDS I can hear +/- a few dB. On the 12,10,6M bands a 20 db S/N was measured and then subtracted 10 dB from the result. This is to eliminate possible signal generator leakage effects. The K3 audio output is very linear with RF signal level input so this is a reasonable thing to do. BAND no preamp preamp1 preamp2 20 -144 dBm -147 x 17 -143 -145 x 15 -143 -147 x 12 -144 -144 -154 10 -143 -145 -156 6 -136 -141 -151 I'm not sure I believe the -15x numbers. Elecraft does say preamp 2 is ultra low noise. Measurement setup: HP-8657B signal generator with additional internal shielding. 20 db attenuator at the generator output. double shielded RG-400 coax to K3 antenna. HP-8657B output verified with an HP-3586C up to 30 MHz down to -122 dBm. Spectrogram on a Delta 44 sound card to measure S/N. Signal measured from K3 line out. YMMV 73 de Brian/K3KO P.S. Switching in the second RX reduces these numbers about 3 dB. On 1/29/2017 3:55 AM, jay Miller wrote: > I assembled my K3/100 with the second receiver in December of 2010. The > weak signal performance was much better than my original IC-756 rig. I did > not install the automatic antenna tuner. I have continued to download the > software changes since then. > > > > Two years ago I installed the general coverage receiver modification. I > thought it was my imagination at the time but I thought had experienced a > slight decrease in the primary and secondary receiver sensitivity. > > > > Today I put my Kenwood TS-480 that I had been using as a mobile in the > shack. I was listing to a couple of weak strength SSB QSOs using the K3. > Out of curiosity I switched over to the TS-480 and was surprised that the > weak signals were more "copy-able" on the inexpensive Kenwood than on the > K3. Does this indicate a problem with the RX in the K3 or is the apparent > difference in the TS-480 RF gain come at the price of the definitely poorer > adjacent signal rejection? > > ______________________________________________________________ > 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 > Message delivered to [hidden email] > 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 Message delivered to [hidden email] |
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Hi,
Frankly I'd be skeptical about all those numbers. They are way better than those measured by ARRL and Sherwood and some are a physical impossibility. The thermal noise floor (kTB) at 400Hz is -148dBm so any number at or below this is physically impossible. To me it looks like all your numbers are off by 10dB or so for whatever reason. I am not sure how you used Spectrogram to measure SNR. All you really need is the dBV meter built into the K3. Assuming it's well designed it should be ideal for measuring RMS power ratios which is what you need. The manual sheets for the XG3 generator from Elecraft has excellent instructions on how to calculate MDS using nothing more than the XG3 and the K3 itself. Of course replacing the XG3 with a professional grade HP generator will not hurt the accuracy of the results. Anyway, this doesn't really explain why you think the K3 has lost sensitivity since the installation of the general coverage bandpass filter board. When I installed mine, I noticed no such effect. If anything this filter ought to have lower loss than the per band RF filters used for in ham-band reception. AB2TC - Knut
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