Problem solved. The RS232-to-USB adapter between the K3 and PC is responsible for 100% of the noise. I now recall running into this issue before with the Elecraft USB adapter used on my LP-100 wattmeter. 10T through a #31 Fair-Rite toroid cleaned it up completely.
Paul, W9AC ----- Original Message ----- From: "Paul Christensen" <[email protected]> To: <[email protected]> Sent: Sunday, July 19, 2009 2:15 PM Subject: [Elecraft] K3 Noise Floor 160m - 75m >I was recently looking at the noise floor of my K3 with SDR-IQ with antenna > disconnected. As I went from the upper bands down to 75m and 160m, I > noticed that the noise floor was not particularly clean on some portions > of > the low bands. I have attached links to two print-screen shots of what I > am > referring to. In both cases, the antenna is disconnected and the pre-amp > is > engaged. I can hear the high noise floor as well as see it on the SDR-IQ > screen, even with the SDR-IQ disconnected. A few more important points: > > 1) The radio is not being coupled to a nearby magnetic field. The shots > taken are isolated from the radio shack and the rig is battery-powered as > is > the laptop PC. Same result when the rig is in the shack and connected to > a > desktop PC; > > 2) The result is the same if I toggle the ANT2 port with no antenna > attached.; > > 3) Although I am sampling the IF with the SDR-IQ, the noise floor remains > with the SDR-IQ completely disconnected from the K3. The only relevant > mod > is the change to the IF voltage divider as described by N8LP; and > > 4) With the pre-amp disengaged, the noise floor drops as expected, but the > noise floor rise as shown in the screen capture is still evident. > > In the first link, I have captured the effect on the upper end of 75m. > Notice that the broadband noise bump is generally just outside the band > but > even so, the noise floor is noticeably higher than when measured down > toward > 80m as shown in the second link: > > http://tinyurl.com/ltyc2o > > Down toward 80m... > > http://tinyurl.com/kpxhgb > > I can replicate this on 160m as well. All other bands are clean. Can > someone confirm this effect by using their K3 (with N8LP buffer mod) and > SDR-IQ unit and get back to me by private E-mail? Thanks! > > Paul, W9AC > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
