The skimmer station is built around the SoftRock SDR RX kits by Tony Parks, KB9YIG<\/a>.\u00c2\u00a0 His basic concept has been refined and has evolved over the 2007-2011 period.\u00c2\u00a0 The simplicity of the hardware and the circuit is fascinating. \u00c2\u00a0The current kit is the Softrock Lite II combined receiver<\/a>.<\/p>\n In the W4KAZ skimmer implementation, several earlier versions of the SoftRock kit are also used.\u00c2\u00a0 Performance of these kits RX sensitivity using ‘regular’ antennas seems on par with the primary rigs(Elecraft K2, A \u00c2\u00a0‘smoke test’ over 2012 ARRL Field day resulted in 14000 station spots on two bands(80m&40m), with no system crash, running two skimmers per dual core CPU. \u00c2\u00a0 Quad core cpu’s will be much more able to handle multiple CW skimmer instances.<\/p>\n The W3LPL RX band pass filters<\/a> are used on all bands, and have eliminated any decoding of out-of-band signals. \u00c2\u00a0These were constructed here with common NP0 ceramic caps[rather than recommended silver-mica’s], hand wound inductors, and tuned by adjusting for minimum SWR on the passband using an MFJ model 259 antenna analyzer. \u00c2\u00a0If there is a fall off in performance due to the ceramic caps, it is not an issue in this usage. \u00c2\u00a0The filters as built are sufficient to eliminate any detectable out-of-band signals on the softrocks.<\/p>\n The preamps are all of the W7IUV design<\/a>. [20150503 Note: a kit version W7IUV amp is available from mtmscientific.com<\/a>] The power supply for the system is a bit lower voltage than recommended for these, using 12.8v where 13.5v is recommended. \u00c2\u00a0No issues from that. \u00c2\u00a0The pre-amp may be too much in this usage – overload of the softrocks and mirror image generation is an issue\/trade-off(see Note#2). \u00c2\u00a0Heat sink the 2N5109, \u00c2\u00a0it WILL\u00c2\u00a0run hot!! \u00c2\u00a0One of these has been running 24\/7\/365 since late 2012, no problems. \u00c2\u00a0Interested now in the IK4AUY design<\/a>.<\/p>\n The small active verticals seem to be a popular solution for a lot of skimmer installations, in particular the short vertical\/preamp from Clifton Labs<\/a>.\u00c2\u00a0 A good product,\u00c2\u00a0 a very good value, and certainly easy to site-locate\u00c2\u00a0 -\u00c2\u00a0 but that $olution, de$pite its bargain price, retail$ for more ca$h than is inve$ted in everything el$e combined.<\/p>\n Not. Happening. Here.<\/p>\n A small vertical is not my personal first choice RX solution anyway, so little heartache(i.e., “none”) is generated over that. \u00c2\u00a0(ed, 20150406, w4kaz,<\/span> but in hindsight it may well be my ‘best’ choice, as a tradeoff . \u00c2\u00a0Too much gain is counterproductive for softrock based CW skimmers.<\/em>)<\/p>\n Instead, the K9AY array was be pressed into regular service for the 160\/80\/40 bands.\u00c2\u00a0 The antenna input from the K9AY array is routed:<\/p>\n For 20m\/15m\/10m the initial antenna will be start off with a coaxial dipole mounted as a sloper.\u00c2\u00a0 A W7IUV pre-amp will be used if it improves performance.\u00c2\u00a0 A magic-t will probably be used as a combiner at the base of the antennas when(if) 15m and 10m are added.\u00c2\u00a0 There will then be a single coax run return to the shack.\u00c2\u00a0 Based on the results with the 20m skimmer, that may revise itself to some other solution.[Revision, 20150406,w4kaz-<\/span> The antenna for 20m\/15m\/10m may wind up being a simple vertical for each band, or \u00c2\u00a0a multi-band vertical fed with a single coax line. \u00c2\u00a0The magic-T type splitter will be used only if the W3LPL RX band pass filters on the front end of the softrocks prove insufficient for signal separation. \u00c2\u00a0Or if there is too much interference generated back up the line by the softrocks themselves. \u00c2\u00a0Hopefully the W7IUV preamps will block some of that.]<\/em><\/p>\n The SoftRocks currently feed their I\/Q signals into a set of two Dell cpu’s. \u00c2\u00a0 40m is into a win XP box running a single skimmer instance. \u00c2\u00a0 160m\/80m\/20m\/15m\/10m are all being run on the second win8.1 computer. \u00c2\u00a0The major difference being the second cpu is a core 2 quad \u00c2\u00a0box. \u00c2\u00a0If it were a more modern quad core, or had an AMD 8 core processor a single unit would be sufficient. \u00c2\u00a0For six skimmer instances I suspect the 8 core processor would be ideal. \u00c2\u00a0Into the current core 2 quad(2 cores with 4 threads) with five skimmers at 96khz bandwidth the CPU load is about 50% on dead bands. \u00c2\u00a0More speculation below<\/p>\n Soundcard\/band pairs<\/p>\n Soundcard\/band pairs<\/p>\n Issue 1]\u00c2\u00a0Load Balancing.<\/span> \u00c2\u00a0 The CPU with the 4 threads <\/span>was an experiment in a couple of areas. \u00c2\u00a0First was to see if were able to handle more skimmer instances than the ‘skimmer03’ cpu that could run 3@96Khz. \u00c2\u00a0Answer: Yes, and quite handily-but….192Khz might be pushing it past its capabilities. \u00c2\u00a0It will probably handle one 192Khz instance and four others at 96Khz. \u00c2\u00a0If it can, I’d rather have it run at least two of the skimmer instances at 192Khz. \u00c2\u00a0Probably set it up for 2015 WPX CW. Load balancing issue.<\/p>\n Issue 2] The sound card issue #1.<\/span> \u00c2\u00a0To run multiple skimmers requires multiple sound card installs(or on the number of stereo inputs for cards with multiple inputs like the M-Audio 44 or 66). \u00c2\u00a0This had previously been a problem with the Xonar DG\/DS\/DX line of cards. \u00c2\u00a0Previously had been unable to get any of the Xonar cards to co-exist with any of the other outboard cards, though they did allow the integrated motherboard sound devices to function. \u00c2\u00a0With a copy of windows 8 available, decided to test if if the Xonars would be better behaved under a current OS(All of the other skimmer cpu’s are\/were win XP). \u00c2\u00a0Answer: Yes<\/span>, but…..The Asus cards seem to require being declared the default device at the time\u00c2\u00a0the skimmer session using it is started, otherwise no joy. \u00c2\u00a0Since the other devices were not conflicting, I just set the ASUS card as the default. \u00c2\u00a0Note:<\/span> Changing the default sound record device changes the order of the devices in the windows sound controls. \u00c2\u00a0Each skimmer’s sound card selection setting needs to be checked after\u00c2\u00a0devices are added to the system or the default sound device is changed. \u00c2\u00a0This includes plugging in a USB card. \u00c2\u00a0The USB device is not always being detected on boot.<\/p>\n Issue 3] Multiple skimmer instances<\/span>, Win8.1, and “Quad” core. \u00c2\u00a0The 960 box is really an early dual core system that imitates being a quad core via hyperthreading. \u00c2\u00a0With windows 8.1, it idles at about 50% CPU usage with five skimmer sessions running. \u00c2\u00a0Also, each skimmer is set to scan only the bottom 90khz of each\u00c2\u00a0cw band via skimmers band plan assignment(bandplan.ini). \u00c2\u00a0Each skimmer is also further limited by setting the number of skimmer decoders to either 200 or 250. \u00c2\u00a0 With 40m on its own seperate box, the natural flow of activity from high bands to low help balance the load. \u00c2\u00a0It should also be noted that the bandwidth being scanned does effect the amount of CPU load, with CPU loads for 192Khz being abut twice the load of a 96Khz bandwidth. \u00c2\u00a0A modern i5 or i7 Intel processor, a xeon box, \u00c2\u00a0or one of the newer 6 or 8 core AMD CPU chips would be ideal. \u00c2\u00a0Still experimenting with the CPU loading combinations on this box as of 20150502.<\/p>\n Issue 4] \u00c2\u00a0The sound card issue #2.<\/span> \u00c2\u00a0Serendipitously discovered(circa 2015-03) a ‘new’ sound card that showed promise based on manufacturer specs, the Diamond xTreme XD71HD series. \u00c2\u00a0Released in 2013(after the initial skimmer builds went ‘live’ at W4KAZ), this newer HD version(s) of the Diamond XD71 card brought with it several\u00c2\u00a0useful features. \u00c2\u00a0It is available in PCI or USB form. \u00c2\u00a0The PCI version is half-height, meaning it could be used in any of the available skimmer CPU’s already in the KAZshack(i.e., minitower or small form factor). \u00c2\u00a0 \u00c2\u00a0They come with ADC chips capable of 24bit 192Khz input, and are highly rated by audio reviewers. \u00c2\u00a0And\u00c2\u00a0the price is very reasonable for a 192Khz capable device, either version available for under $50USD(sometimes). \u00c2\u00a0BAM! \u00c2\u00a0Both versions work very well at any bandwidth, and both can coexist with each other as well as a Soundblaster and Xonar.<\/p>\nFT-920,<\/del><\/span>TS-590s) on 160m thru 20m. \u00c2\u00a0They are somewhat less sensitive on 15m and 10m. \u00c2\u00a0Their selectivity can be compromised by overload from strong signals, which is seen as a “mirror image” on the opposite side of the center frequency. \u00c2\u00a0The best of the skimmers here have shown themselves to begin showing mirror images whenever the SNR of the skimmer approches 45db.<\/p>\nPreamps and bandpass filtering:<\/h5>\n
Antennas<\/h5>\n
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CPU’s -\u00c2\u00a0Being Revised 20150502<\/span><\/em><\/h4>\n
skimmer03 – dell optiplex 360 minitower(pentium dual core e2200, Win XP Pro Sp3+)<\/span><\/h5>\n
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\nMAudio delta 66 \u00c2\u00a0 \u00c2\u00a0 \u00c2\u00a0 \u00c2\u00a0 \u00c2\u00a0 \u00c2\u00a048\/96(@96khz)………………..[40m, 7.055015 center, occasional use at 192khz bandwidth]<\/span><\/li>\n<\/ol>\nskimmer04 -\u00c2\u00a0Dell OptiPlex 960 SMT, 2.66 GHz Core 2 Quad, Win 8.1<\/h5>\n
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General Discussion\/Lessons Learned\/”fiddley bits” \u00c2\u00a0Being Revised 20150502<\/span><\/em><\/h5>\n