[Skimmertalk] Skimmer Advice (K3 IF issues)

Bob Wilson, N6TV n6tv at arrl.net
Mon Nov 9 20:27:02 EST 2015

It sounds like you want both a waterfall display wideband band scope *and*
local skimmer spot decoding to happen at the same time, on multiple bands,
using your present equipment.

See my online presentation for some ideas, but it sounds like you already
have most of it:

   - Adding a Software Defined Radio (SDR) to an SO2R station
   - Using Waterfall Displays as a Contesting Advantage

In sum, for fixed Waterfall display, I recommend a passive (or active) RF
splitter on K3 RX IN/OUT line, feeding any SDR and running it with HDSDR or
WinRad as the band scope, instead of CW Skimmer.

For multi-band spot decoding, use SkimmerServer on a multi-band antenna,
such as the Pixel loop or a tribander, and a QS1R (plus telnet to an RBN
node such as VE7CC).

There's no need to use any Rx Guard between the K3 RX ANT Out and SDR
Antenna inputs, because there is never RF output there (other than bleed
through).  Using an Rx Guard does no harm, but it's not needed.  If you
have bandpass filters on the main K3 TX output, there's really no way for
high RF to get to the SDR, unless you have second transmitter on the same
band on an very nearby antenna (which seems unlikely).

Using a Pixel Loop, the loop's power control box can by keyed with your PTT
line on the K3, and that will remove DC from the Pixel preamp every time
you transmit (works OK at QSK speeds).  So again, with that set-up, no need
for an RX Guard on the SDR.

Re. CW Skimmer, it *does* decode all 192 kHz, but you can only *see* about
12 kHz on the Skimmer waterfall at a time, and you can't zoom in our out.
However, you can press the [PageUp] or PageDown] keys while CW Skimmer has
to focus to see the rest of the decoded frequencies.  To see "blips" (no
waterfall) of the *entire* spectrum being decoded, start CW Skimmer and
select View -> Bandscope from the menu (most folks have never tried that
option, but they should).  You can then click on any signal in the band
scope window to retune the SDR to that frequency, instead of pressing
PageUp and PageDown.

Regarding having the cursor on the Waterfall follow your radio's tuning
knob, it's easy to do with contest software the supports OmniRig, since
HDSDR and WinRad also use OmniRig, but that solution will not work with
N1MM+, because N1MM+ does not support OmniRig.

I'd would recommend instead a P3 scope.  Maybe you can treat yourself to
one this Holiday Season. ;-)  Maybe sell one of those extra SDRs to get the
funds for one.

For multi-band spot decoding SimmerServer, you need a QS1R SDR, or one of
the other supported models.  The QS1R is the only one that can decode seven
bands at once.  Or you could dedicate one SDR to each band.

Bob, N6TV

On Mon, Nov 9, 2015 at 3:26 PM, Pat Rundall <pat at n0hr.com> wrote:

> Skimmer Gurus...
> I'm looking for a bit of advice on how to improve my setup for CW contests.
> Namely, I'd like to avoid the 24khz limit of the k3/LP-Pan setup and issues
> with the output shifting frequencies when I change filter settings on the
> k3.
> The Goal:
> Aggregate useful skimmer spots -> N1MM+ for the current and adjacent bands.
> I'd prefer to have the skimmer running on the active antenna (ie a beam
> rather than a short vertical or loop)
> The Current Setup
>    - N1MM+ on a laptop
>    - K3/100 as the main rig w/RX2
>    - LP-Pan2 from IF-Output of K3
>    - USB sound card capable of 192khz
>    - Currently, I'm routing the RX output of the k3, through a
>    DX-Engineering RX-Guard and then into the RX input as a means of
> protecting
>    the front end in a SO2R environment (also using BPFs, etc.). (100w)
>    - Aggregating spots from a local packet node with wintelnetx
> Other HW available
>    - Afedri SDR
>    - Pixel RX loop
> The problem
> I noticed in Sweepstakes CW that the Skimmer is only decoding +/-12khz
> rather than the whole 192kHz at once. Also noticed that when I change
> filter settings on the k3, the frequency jumps on Skimmer. I've read where
> both of these issues are known and there really isn't a working solution
> apart from simply using other hardware. Unless I've missed it, I don't see
> a solution to these issues offered by the vendors (Elecraft/LP-Pan/VE3NEA)
> Options
>    1. Setup the Afedri SDR to be a standalone receiver by putting a
>    splitter after the RX-Guard on the RX-out/in loop. I may see a bit of
>    signal loss on that. I'd probably setup the Afedri on a separate PC
> running
>    an SDR app (HDSDR?) with Skimmer. Then when I change bands, manually
> change
>    that on the app. Not horribly inconvenient.
>    2. Setup the SDR on the RX loop with another RX Guard. (Even if there is
>    a fix to the K3 IF issues, I may setup another SDR on the loop to
> monitor
>    the adjacent band)
> Other thoughts?
> Thanks
> Pat N0HR
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