K3 NB and Digital Reception

[vk4cmv]

The other day I was receiving a very loud (S9+10) Jt65a signal from a local station and was noticing that his signal seemed to be modulated by a commercial radio station. So I was just about to send him an email saying that he had a problem, when I adjusted the RF gain, turned the ATT on and turned the PRE off. His signal was now sweet.

So I switched to another sound card - and still the same result after I had reset the controls again.

Then  I remembered that I had set the NB on (dsp off) and IF to Wide 7 and as soon as I had turned the NB off, his signal was copied just fine. What I found was that setting the IF to Wide 7, Med 7 or Nar 7 gave rise to what only can be described as intermodulation.

The reason I use the NB at all is because my neighbour has one of these solar pads that heats his swimming pool on his roof, and the pumps in it generate this ta-pocketa-pocketa-pocketa noise (like an electric fence, but faster) - and I just leave the NB one most of the time, because my neighbours also own behemoth plasma TV sets :)

So two questions:
 1) has anyone else noticed spurious intermodulation in DATA mode when the IF NB is set to the 7 level - or have I got a fault?, and
2) Is there a beginner's guide to help me understand how to use the NB effectively - at the moment, I just spin the dials until the noise is gone.

thanks, Julian VK4CMV

[Guy, K2AV]

The IF setting of NB in the K3 is a traditional shut-down-the-IF
blanker and will always exhibit that behavior. A strong enough signal
will modulate it. Turning on PRE takes away from the headroom
needlessly below 10 meters. Keep the ATT/PRE/RFGAIN low enough that
ambient noise is moderately low. That's good medicine for a lot of
things and proper operating for a K3.

Lower the ATT/PRE/RFGAIN:  ATT on for 160 through 40, nothing for
20-15, PRE only for 10 and 6. Also on 160 and 80, setting RFGAIN to
two or three oclock may help to set ambient noise moderately low. If
this does not work, then try turning off IF blanking and use one of
the DSP NB settings instead.

Running PRE on the low bands is simply not needed unless you are using
a low gain RX ant that needs a boost.  Unless you are living in a low
noise paradise  :>)

73, Guy.

On Fri, Feb 5, 2010 at 9:33 PM, vk4cmv <[hidden email]> wrote:

>
> The other day I was receiving a very loud (S9+10) Jt65a signal from a local
> station and was noticing that his signal seemed to be modulated by a
> commercial radio station. So I was just about to send him an email saying
> that he had a problem, when I adjusted the RF gain, turned the ATT on and
> turned the PRE off. His signal was now sweet.
>
> So I switched to another sound card - and still the same result after I had
> reset the controls again.
>
> Then  I remembered that I had set the NB on (dsp off) and IF to Wide 7 and
> as soon as I had turned the NB off, his signal was copied just fine. What I
> found was that setting the IF to Wide 7, Med 7 or Nar 7 gave rise to what
> only can be described as intermodulation.
>
> The reason I use the NB at all is because my neighbour has one of these
> solar pads that heats his swimming pool on his roof, and the pumps in it
> generate this ta-pocketa-pocketa-pocketa noise (like an electric fence, but
> faster) - and I just leave the NB one most of the time, because my
> neighbours also own behemoth plasma TV sets :)
>
> So two questions:
>  1) has anyone else noticed spurious intermodulation in DATA mode when the
> IF NB is set to the 7 level - or have I got a fault?, and
> 2) Is there a beginner's guide to help me understand how to use the NB
> effectively - at the moment, I just spin the dials until the noise is gone.
>
> thanks, Julian VK4CMV
>
>
>
>
> --
> View this message in context: http://n2.nabble.com/K3-NB-and-Digital-Reception-tp4523714p4523714.html
> Sent from the [K3] mailing list archive at Nabble.com.
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[W7GJ, Lance]

Hello Julian,

I also noticed the other day that I was hearing a "whoosing" in the background on
a CW station that I never heard before.  I was afraid I had blown a preamp or
something.  I finally found that I had set the NB on Wide 7, and as soon as I
turned it off or back to Nar 1, the problem disappeared.

So something must have changed in the NB operation in the latest Firmware.  I also
found last weekend when I switched to 144 MHz in the transverter mode for an EME
sked, that my audio output from the LINE OUT suddenly seemed to be 15 or 20 dB
down on that band, as compared to 6m.  That had never been a problem before.  I
don't know if that is also related to the Firmware version or not.

In the last week I also found that the noise level seemed to come up higher and
reduce signal strength of incoming signals I use as reference (6m beacons).

Anyway, I still use the same firmware version, but I re-loaded a Configuration
file that I had saved several months ago...and readjusted the LINE OUT level in
the CONFIG menu.  That seems to have solved the problems except the one with the
NB.  Now I have to be very careful not to use the Wide 7 NB setting.

GL and VY 73, Lance


On 2/6/2010 2:33 AM, vk4cmv wrote:

>
> The other day I was receiving a very loud (S9+10) Jt65a signal from a local
> station and was noticing that his signal seemed to be modulated by a
> commercial radio station. So I was just about to send him an email saying
> that he had a problem, when I adjusted the RF gain, turned the ATT on and
> turned the PRE off. His signal was now sweet.
>
> So I switched to another sound card - and still the same result after I had
> reset the controls again.
>
> Then  I remembered that I had set the NB on (dsp off) and IF to Wide 7 and
> as soon as I had turned the NB off, his signal was copied just fine. What I
> found was that setting the IF to Wide 7, Med 7 or Nar 7 gave rise to what
> only can be described as intermodulation.
>
> The reason I use the NB at all is because my neighbour has one of these
> solar pads that heats his swimming pool on his roof, and the pumps in it
> generate this ta-pocketa-pocketa-pocketa noise (like an electric fence, but
> faster) - and I just leave the NB one most of the time, because my
> neighbours also own behemoth plasma TV sets :)
>
> So two questions:
>   1) has anyone else noticed spurious intermodulation in DATA mode when the
> IF NB is set to the 7 level - or have I got a fault?, and
> 2) Is there a beginner's guide to help me understand how to use the NB
> effectively - at the moment, I just spin the dials until the noise is gone.
>
> thanks, Julian VK4CMV
>
>
>
>

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]   URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

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