[PVRCNC] SKIMMER/K3

[Jim Jordan, K4QPL]

Brian and all,

I can admire the engineering and the technology. Good work.

But as it finally evolves I'm not so sure what it does for contesting.

I consider regular packet as pretty much catching in a barrel fish that 
someone else has seen (and which may or not be seen from your qth). I guess 
a local skimmer putting them on the MM bandmap is going to be like someone 
also putting them on the hook for you to just pull out.

Will someone please complete the technology to finish the job and get 
everything fixed up to make/log the exchange with the other guy's radio also 
using Skimmer so I can read a book while my equipment handles that boring 
and/or difficult stuff. I'll check my score on 3830 later!     (TIC)

Another thought. Why don't they put motors on those America's Cup sailing 
yachts? Yamaha makes some really good ones.

73,

Jim


----- Original Message ----- 
From: "Brian Alsop" <alsopb at nc.rr.com>
To: "PVRCNC" <pvrcnc at mailman.qth.net>
Sent: Saturday, February 13, 2010 5:03 PM
Subject: [PVRCNC] SKIMMER/K3


> Guys,
>
> Been playing with of couple of the $18 SDR kits.  One for 20M and one
> for the K3 IF.
>
> Looking at just a spectrum display is kind of boring.  Add call signs
> and it becomes useful.  So I decided to try SKIMMER.  Having spots for
> stations actually heard at your QTH is quite useful.
>
> The below observations have probably been recorded elsewhere. Every
> generation seems to have to relearn what the OT's already knew. I'd like
> feedback.  The below may show my ignorance. I may have gone down faulty
> paths and there are work-around's.
>
> -1) You need a decent stereo sound card. Here, one PC's motherboard
> worked only at 48K sampling rate.  Crummy dynamic range too. Another
> PC's motherboard sound card was mono!  You need stereo for SDR's I and Q
> outputs.  Ended up with a $100 PCI sound card which was suppose to be
> "low cpu use".  The E-MU 202 USB sound card apparently is a buss hog.
> They recommend using it in these applications only an multicore CPU
> machines.
> 0) When hooked up to the 20M SDR, SKIMMER blew my socks off.  Decoding
> the entire 20M CW band at once and putting it on a band map.  Even Don
> Miller couldn't do that.  I suspect these could be exported via TELNET.
> The sensitivity and selectivity of the combo were quite astounding.
> The decode worked well even with signals that were faint on the
> waterfall.  It also used 80% of the CPU cycles.
> 1) SKIMMER and N1MM do not work together on a 2.8 GHz, 2GB memory, 1 CPU
> machine running WIN-XP.  Both load OK but N1MM then looses the radio and
> then become unresponsive
> 2) SKIMMER is pretty useless until you get it to export spots to N1MM.
> Telnet is the suggested way.  Some additional program has to merge
> ordinary spots and SKIMMER spots.  WRITELOG apparently allows two
> sources of TELNET spots and an external spot merge program isn't needed
> for WRITELOG.
> 3) When hooked up to the K3 IF (via a Clifton labs z-10000
> preamp/isolation buffer) SKIMMER will only decode +/- 12 KHz from the
> present K3 transmit frequency.  This is a SKIMMER, not K3, limitation.
> You have to tune to get more of the band.  So if you're running them,
> you have to find a way to get more of the band decoded. See (4). If you
> use LP-BRIDGE, you can share K3 frequency info and click on the SKIMMER
> band map to pounce on a spot.  Likewise these can be exported to TELNET
> and imported to N1MM.
> 4) Given observation (1) above. Either get a macho PC or do as Mark N2QT
> just finished doing.  Run SKIMMER on a standalone PC and link to the K3
> via LP-BRIDGE over a null modem RS232 cable between the contest and
> SKIMMER PC.  Mark has hooked the K3's subrx IF to his SKIMMER to get
> around the +/-12 KHz SKIMMER "IF radio" limitation. He is going to tune
> around with the subrx anyhow.
> 5) One Caribean DX station is or has planned using stand alone SDR's for
> each band.  These are somehow connected to separate antennas and not
> blown up by the RF when transmitting.  This gets around the +/-12KHz
> limitation.  If these SDR's are muted, it is hard to figure out how they
> get anything to decode -- since these guys "run" nearly 100% of the time.
>
> Practically speaking, having to use SKIMMER via two PC's IMHO is too
> much of a pain.  In fact, the whole thing seems pretty much like a house
> of cards- but promising. Too bad SKIMMER & soundcard were not in one
> standalone box thus avoiding both CPU hits.  Input IF, output spots via
> USB.  SDR-IQ/Spectravue comes closer to this.  Spectravue's
> documentation is quite overwhelming, BTW.
>
> 73
> de Brian/K3KO
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