+++++++++++++++++ From: "Wallace, Andy" To: "'Elecraft'" Date: Thu, 13 Feb 2003 07:50:53 -0500 Subject: [Elecraft] K2 rev B sensitivity - measurements look ok! OK, took some sig gen measurements. Recall that the ARRL K2 review said that an S-9 reading was with 115 uV in on 20m, preamp off, and 19 uV, preamp on. Here are my results for all bands: 80 115 21 40 115 17 30 100 17 20 125 20 17 125 22 15 130 25 12 150 26 10 140 21 The minimum discernible signal on 80m seems to be less than 0.1 uV. This was with the S meter hi cal = 018 and s meter low cal = 179 (done on 40m, no antenna, preamp off). The numbers above were with FL1 set to 1.5 kHz. Some loss up around 12/10 but that could also be loss in the old BNC cable from my signal generator, or the sig gen itself. Been years since I used or calibrated it so I should check it with a scope to see if the attenuator is accurate. Overall, I think it matches the ARRL spec close enough. Guess it's not deaf after all. If anyone else wants to check theirs after all, I'd like to hear what your numbers are. -Andy +++++++++++++++++ From: "Dave Sergeant" To: elecraft at mailman.qth.net Date: Thu, 13 Feb 2003 15:44:43 -0000 Subject: [Elecraft] K2 rev B low sensitivity Andy Wallace wrote: >I would like to hear from anyone else on the List who can run that >measurement. With a properly calibrated (by the manual) S meter, >what is your input level for S-9 signal with preamp on and off? >Thanks... I have just done this test on my rev A K2 (#2498) with the following results: Test frequency 7002, CW 400Hz filter (the one I use all the time) Generator Gould SSG220 Level to just illuminate S9 LED Preamp off -63dBm or 159uV Preamp on -78dBm or 28uV Slightly worse than the ARRL figures, but they were possibly in an SSB filter, but taking into account the various errors seems in the same area. Measuring the noise floor sensitivity is harder as my generator only goes down to -132dBm without external attenuation (and it can certainly hear that) so I have not done that. I tend to use the preamp all the time, but my antenna (60ft long wire) is hardly receiver overloading stuff. 73 Dave G3YMC dsergeant at iee.org dsergeant at btinternet.com http://www.dsergeant.btinternet.co.uk ++++++++++++++++++ From: "Wallace, Andy" To: "'Elecraft'" Subject: RE: [Elecraft] K2 rev B low sensitivity Date: Thu, 13 Feb 2003 12:35:08 -0500 > -----Original Message----- > From: Ron D'Eau Claire [mailto:rondec at easystreet.com] > > Select your narrowest filter. > > Turn up the gain so you hear "band noise" - the background QRN that is > always there. > > Disconnect the antenna. > > If the noise level drops noticeably, you K2 is hearing as well as any > receiver with a similar bandwidth. Great point, Ron. Actually I had thought of your earlier posts on the subject when doing the signal tracing. After resoldering the Q22 area and having good sensitivity again, I did verify that on 80 and 10 I could hear the difference with the antenna connected vs. not. > SOME K2's seem to have relatively low audio system gain. Ops complain > that they have to run the Audio Gain control way up - almost > full "open" to get adequate gain Well with the preamp on, both my K2 and the K1 are comfortable to listen to -- through their speakers -- at about 9:00. (Before resoldering the Q22 area, it was more like 12:00.) My difficulty was not having a K2 to compare to -- I would hate to have this rig for years and then discover it wasn't as nice as it could have been due to a construction error/fault. Before resoldering Q22/C161/RFC11, it took over 300 uV to get S-9 on 40 with the preamp off. Now it's 120 or so....quite a difference! > Using a pre-amp when you don't need one means > that you are reducing the dynamic range of the receiver. Understood -- in my case I am using a terrible antenna, just 35' long, with no prospect of improvement anytime soon. So I may need to use the preamp in most cases. Hopefully the KAT2 will help, as much as the KAT1 helps my K1 on receive. > But that is not a good indicator of whether your K2 can > "hear" weak signals as good as another receiver. Of course -- but by calibrating "by the book" and injecting a signal of x microvolts for S-9, it gives people something to use for comparison. The best reference would be oscilloscope shots of what to expect in the signal path for a given input. Thanks, Ron. I've stopped worrying and now I can look forward to filling all the empty connectors inside. :-) Andy ++++++++++++++++++++