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K3 Noise Floor 160m - 75m

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P.B. Christensen

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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P.B. Christensen

Re: K3 Noise Floor 160m - 75m

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" <[hidden email]>
To: <[hidden email]>
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:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Brett Howard

Re: K3 Noise Floor 160m - 75m

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" <[hidden email]>
> To: <[hidden email]>
> 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:[hidden email]
> >
> > 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:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

P.B. Christensen

Re: K3 Noise Floor 160m - 75m

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

I just finished winding 10T through the largest #31 clamp-on sold through DX
Engineering. Tight and even turns will get you there. It's located right
at the K3's RS-232 port. However, there's still not enough choking
reactance to bring the noise floor down all the way. So, there may be a
direct path of RFI through the connector.

Admittedly, I am being fussy here because an antenna connected to the K3
masks the problem. But, I'm still bothered with the problem since the K3
should be immune to a device connected through its RS-232 port. From here,
I see two possible solutions:

1) Adding an RS-232 card to my PC thereby eliminating the USB converter; or
2) Using an opto-isolated RS232-to-USB converter. I found a couple on the
web, but these are big $$$ devices.

Either way, there's no guarantee that either choice will completely mitigate
the noise. My K3 is current with grounding mods and it also has the new
remote KIO3 board. I'll keep experimenting....

Paul, W9AC

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