Hello Sverre Thanks for putting your spectral analysis on the web page. It's very interesting and I decided to do my own test. I used Spectrum Laboratory, but it displays similar information to Spectran.
I have deviated from white or pink noise, because most of the time we are listening to real signals (or qrm!). I decided to inject a signal: I used my K3 and XG1 to perform the test. The line out from the K3 was connected to line in on my PC. With reference to a fundamental audio signal at 0db, a third harmonic of this was observed at about -40, and a fifth harmonic at around -50dB. The even order harmonics are well down in comparison. I don't know if this is a good result or bad. But it's clear to me that if I am listening to a 700Hz CW note, no amount of audio roll-off at 4kHz or so is going to change the relative levels of those first few harmonics. Just for fun, I ran the same test using an FT-847. The results were very different. Firstly, harmonics were down at -55 or better. Secondly, the even order products (2nd and 4th) were louder than the odd ones. And lastly, the FT-847 graph showed several close-in spurious alongside each harmonic, which had been completely absent with the K3. I hope this all makes sense. And apologies if my use of technical terms is not spot-on. I'm just an amateur, with no training in electronics or radio ! Regards John G4ZTR -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Sverre Holm (LA3ZA) Sent: 20 December 2009 13:13 To: elecraft@mailman.qth.net Subject: Re: [Elecraft] [K3] K3 Receiver Noise Level -- Evaluation and Adjustment Concerning the last few days' discussion of noise and artifacts, here is a spectral analysis plot of my K3's output: http://www.qslnet.de/member/la3za/bilder/K3-CW-spectran.jpg First it shows the signal related artifacts in the 10-13 kHz range as mentioned by Wayne N6KR below. It also shows line noise at approximately every kHz (harmonics of 1.025-1.030 kHz). The highest of these is at approx 2050 kHz and is at about -40 dB relative to the main signal, i.e. at a level of about 10^(-40/20) = 0.01 or 1%. Thus these lines could be audible and be part of the explanation for the complaints about the K3's sound. Apart from the lines, the background is down to -60 dB above 2-3 kHz. It is interesting to note that my spectran plot has discrete line noise as opposed to that of G4ILO in his blog from today (http://www.g4ilo.com/blog.html), plot here: http://www.g4ilo.com/uploaded_images/k3freqresponse-736797.gif . His background noise level is similar to mine. Could this be due to differences in individual K3's as has been hinted to on this list? My setup is: K3 with PRE on at 14.102 MHz, RF gain at max, CW with 400 Hz roofing filter and bandwidth set to 400 Hz, AGC-F on and with AGC parameters SLP=9, THR=3, I use a lot of averaging in Spectran to make the lines more visible as seen from the setup info in my plot wayne burdick wrote: > > This filter rolls off everything at about 4.5 > kHz, including some low-level AF sampling artifacts from 10-14 kHz > that some operators with excellent ears can hear. > ----- Sverre, LA3ZA http://www.qslnet.de/member/la3za/K2/mod.html LA3ZA Unofficial Guide to K2 modifications -- View this message in context: http://n2.nabble.com/K3-Receiver-Noise-Level-Evaluation-and-Adjustment-tp418 7070p4194554.html Sent from the [K3] 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 __________ Information from ESET NOD32 Antivirus, version of virus signature database 4702 (20091219) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus signature database 4703 (20091220) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.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
