[Elecraft] K3 Noise Floor 160m - 75m

[Brett Howard]

Holy cow 10T?  Thats a big chunk of iron.  Kinda surprised you had
enough cable length for that... :)

On Sun, 2009-07-19 at 15:01 -0400, Paul Christensen wrote:
> 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" <w9ac at arrl.net>
> To: <elecraft at mailman.qth.net>
> 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
> >
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