Radio W4KAZ

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W4KAZ Softrock Based CW Skimmer Station – 01) General Approach

Original from 2012/5, updated 2013/05/13, 2015/04/02, 2015/05/03 kaz

see the current W4KAZ Skimmer spots via the RBN

Re: The ongoing Quest of having a local station pushing CW spots into the Reverse Beacon Network.

CW Skimmer combined with the Reverse Beacon Network is a really slick combination for monitoring real world propagation, band activity, contest spotting, and general curiosity.  Great stuff.   AC0C published his project information (then click “CW-Skimmer Array” in left sidebar)  for building a CW skimmer based on SoftRocks.  His skimmer station is essentially a scaled down version of the bleeding edge skimmer station previously built at K3LR based on the Persues SDR. In the end he determined that the QS1R(new at that time) was probably a more cost effective and easier approach.  I agree.  The QS1R is probably the optimum solution currently available.  (ed, w4kaz – even more true today 2015/04/02)

Unfortunately, the optimal solution(QS1R + fast Quad Core i7 computer+ OS + yada-yada-yada) is also expensive enough to be beyond the available ca$h $upply out here in the cheap seats.  For example, PJ2T has an itemized list of expenses for the PJ2T skimmer build circa 2009/2010(Note: does not include man-hours).    The available “radio toy budget” in the KazShack was the amount of cash that had been budgeted for the then canceled 2012 IOTA Core Banks expedition – about $150.

Only$3.7k short of the PJ2t build budget – Yikes!     OK….  Alternatives?  Anything different in 2012 over 2009?

What a difference a few short years made.  At this point(2012) the AC0C method(circa 2009) has become a lot less expensive in term$ of initial ca$h outlay$ due to the gift of Moore’$ Law –  i.e., dual core computers are now being retired for fast quad core boxes, and the CPU part of the investment is now relatively minor.  People are throwing them away.

AC0C’s notes make points regarding the amount of time investment required for the project. Time expenses are also relevant.  But in my case, the time spent on the project is an educational/fun investment.  Part of the goal is the “doing” – at least as much as the physical end product.  So that is not included in the personal calculation as an “expense”.  Here the time investment is part of the desired result.

The tipping point  to actually start the project came when I diverted from landfill/recycle a pair of dual core CPU’s,[Dell’s – for free], being retired for upgrades by a friend.  Zero invested there[well some beer drinking WAS involved – oh! the horror….the horror….].

Another unexpected holiday gift of a Softrock v6.2 simultaneously tweaked the interest.  A recent AE5X tip about NorCalQRP offering SoftRock Lite kits as a fundraiser broke the camels back.  A bit of sniping on the Dell auction site brought in another fire-sale priced CPU to complete the set of three.  [Softrock kits are now generally available from Tony Parks, KB9YIG, via Five Dash Inc, 5/2013]

The W4KAZ skimmer station was originally built on the idea of running two softrocks on each computer, with three computers required for skimming all six contest bands[160/80/40/20/15/10].  That allows using the on-board sound card and a single add-in sound card.  It also provides a bit of built in redundancy.  A single computer failure does not necessarily completely incapacitate the station.  The downside of that is running three computers, drawing ~200watts of juice apiece. Mitigating the downside, the current expectation is that one pair of skimmers will run 24/7/365, with the others only active over selected weekends and/or contests. Updated, 20150503 – The skimmer station is now reduced to two computers.  One box running winXP and a 40m skimmer.  The second is a Core 2 Quad running Win8.a, and is supporting the other five contest bands.

Oh yeah….the Softrocks require some tweaking to get them onto 15m/10m.

Softrocks also require soundcards for the SDR signal processing.  The Asus Xonar line was initially chosen as the add-in sound card of choice for its low price, small form factor, and good “on-paper” specifications.   The form factor limitation was due to the nature of the acquired CPU’s.

After firing up the first xonar(Xonar DG) with the MP3 collection, it became the obvious first choice.  In my ears it is easily the best sound card price/hi-fi-performance value available.  It has much better fidelity than any SoundBlaster I have had over the years, and this is from the bottom of the line ASUS sound card.  It really rocks in NumberOneSon’s Sennheiser headsets. [Damn things sound great, and only$22USD – before the $10 rebate!  Highly recommended for music.]  [ed, w4kaz, 20150402 – There are a few more choices available now, and some have been tested.  But the Xonar DG is adequate if the limitations are acceptable.]

With the initial computer costs limited, building a rudimentary skimmer station became viable in 2012.  The largest single out-of-pocket expense turns out to have been the VE3NEA CW skimmer license itself.  It is worth every penny, as Alex has written a simply brilliant piece of software there.  The folks working on other pieces who have built the Reverse Beacon Network have also done  a wonderful job of making a treasure trove of propagation data available.  [ed, w4kaz, CPU and OS expenses are also significant if they need to be acquired new]

Initially the expectation was to build the station piecemeal, one skimmer at a time.  The availability and timing brought most of the hardware required to the doorstep in a relatively short time.  The major delays are related to finding time and energy to assemble all of the pieces/parts.

160m thru 15m became active in 2012 and are supported with a mix of current and original SoftRock kit offerings.  Better 15m and 10m solutions are possible if a suitable oscillator can be found.[ed, w4kaz 20150402 – si570 programmable oscillator!]  Several oscillator solutions are plausible, but those issues and those  bands will be the last problems to be resolved.  Possibly a retroactive overhaul of the 20m kit as well.

Other Skimmer stations:

  1. K3LR
  2. AC0C
  3. KH6LC
  4. PJ2T
  5. W3OA
  6. AA4VV
  7. W4AX
  8. WA7LNW
  9. WZ7I
  10. OL5Q
  11. K8ND general skimmer info links
  12. ZL2HAM

Have one to add to the list?  Put it in a comment or send using the ‘Contact W4KAZ’


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