Hi group, I bought a used K2 some time ago. I've not used it much but it seemed to work fine. I recently upgraded it with the SSB option and the 60m/transverter option. I had to go through the BFO re-alignment procedure in order to make the filters work properly after installing the SSB option, and this process seemed to work quite well. The added options appear to be working OK and I was able to make a few CW and SSB QSOs.
However, I noticed that the S meter was not moving very much so I thought to check the sensitivity. According to the spec we should have a sensitivity (MDS) of something like -130dBm without the preamp and -135dBm with the preamp. I have an HP signal generator and, without being too precise about MDS etc, I was not able to hear anything at all below about -120dBm (ie the signal was completely buried in the noise) and it would probably take -110dBm to -100dBm to be able to copy a signal. This is with the preamp on. So I am looking for reasons why my sensitivity is a bit down, say 20 to 30dB. My K2 has, in addition to the SSB and 60m options, the noise blanker and top band options as well as the KPA100 and KDSP2, which were not in use during these checks. I was able to make the following observations: a) The sensitivity is about the same on all bands which would seem to exclude the 60m module as a potential source of the problem. b) The sensitivity is the same using the separate receive antenna input in the top band option. c) The transverter option does not appear to be causing the problem since I can use it to switch between the transverter input and the normal BNC antenna connection. d) The sensitivity seemed to be slightly better using the SSB filter than the CW filters. By the time the 200Hz crystal filter bandwidth was selected the signal was audibly weaker than using the fixed SSB filter. I'm not all that familiar with the K2 architecture and particularly the alignment procedure. So I should like some advice about the best way to approach this issue. I see that the noise blanker has an IF filter (labelled -6dB) which I imagine could cause a problem like this if it was built incorrectly. I guess it is an easy enough step to remove the option and replace it with a wire link. Assuming that this did not resolve the problem, would I be wise to look for a definite fault (eg in the IF amplifier chain) or to go down the path of complete re-alignment? Can poor alignment (excluding front-end alignment) of the radio cause poor sensitivity? Could this be the reason why the CW filters seem less sensitive than the SSB filter? Bear in mind that there could be an original build fault causing this issue (perhaps a wrongly wound matching transformer, for example). Thanks in advance for your help. Paul -- View this message in context: http://elecraft.365791.n2.nabble.com/K2-Poor-sensitivity-tp7622862.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
