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Delta 1010LT - individually selectable inputs from windows apps? sound card for multi-sdr array -

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  • Jeff Blaine
    Victor, That is a fantastic project you are working on. Way, way beyond what I am trying do. Really fantastic... A couple of my extreme-antenna buddies were
    Message 1 of 8 , Jun 7, 2009
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      Victor,

      That is a fantastic project you are working on. Way, way beyond what I
      am trying do. Really fantastic...

      A couple of my extreme-antenna buddies were very interested at your site
      after I mentioned this project of yours to them.

      I realize you are using Linux below. But I am wondering if, under
      Windows, if the ASIO driver enumerates the inputs individually?

      I have an otherwise exellent Quartet with dual inputs - but the inputs
      are only individually selectable under certain high-end a/v programs.
      For generic windows applications (like CW skimmer and PowerSDR), they
      only see the ASIO driver as a single entry - meaning only the first set
      of inputs and the first set of outputs are useable in "the real world."
      The Quartet guys say a driver revision that will allow individual
      selection from the generic windows app "is coming soon." Yes, "coming
      soon" and we know what that may mean... :)

      PowerSDR also lets a guy select the MME for inputs, but the Quartet
      driver in that case also just provides a signle input/output pair listed.

      I am hoping the Delta card does not have that problem... But sure want
      to confirm it before heading off to buy yet another pretty pricy sound card.

      Thanks

      73/jeff/ac0c


      73/jeff/ac0c

      Victor A. Kean, Jr. wrote:
      >
      >
      > I observe that some people are contemplating experiments with multiple
      > SDR receivers. I have been running 8 Softrock equivalent receivers
      > using 2 Delta 1010LT sound cards on a Linux machine for about a year
      > now. Basically, it works, but there are issues. If I share my
      > experience, maybe I can save some people a lot of time and trouble.
      >
      > The Delta 1010LT is based on the same Envy24 or ICE1712 chip that is
      > used in the Delta 44 and the Delta 66. Also, the same Linux driver is
      > used for all of these cards. The Delta 1010 has 8 analog inputs and 8
      > analog outputs. It also has a pair of SPDIF inputs and a pair of
      > SPDIF outputs, which gives a total of 10 input channels, and 10 output
      > channels, hence 1010. For SDR purposes, one card supports 4 receivers.
      >
      > I have an operational 4 SDR receiver setup which I use along with 4 2
      > element end-fire arrays of short verticals to do beam steering on 160
      > meters. Look at k1lt.com for more information about that activity.
      >
      > I have been working on an 8 SDR receiver setup to use with a circular
      > array of short verticals. This requires 2 Delta 1010LTs, and requires
      > that the 1010s be "phase locked". Fortunately, the 1010LT supports
      > this requirement with a feature called "word clock". The 1010 has a
      > word clock output and a word clock input, so that one card can be the
      > master sample clock and one or more other cards be the synced to the
      > master. One can also do phase locking with the SPDIF inputs and
      > outputs, so theoretically, a pair of Delta 66s can be locked together.
      >
      > Supposedly, SPDIF locking causes more phase jitter than using the word
      > clocks, but I haven't yet noticed, for reasons that I explain below.
      > One uses the envy24control utility to configure one card to be the
      > master and the other to be a slave. One also uses ALSA configuration
      > file tricks to make multiple physical sound cards appear to be one
      > logical sound card to audio applications, such as JACK.
      >
      > The ICE1712 driver on Linux supports up to 4 cards.
      >
      > When working with phased array, calibrating sources of phase error
      > becomes a major chore. Each Softrock has a slightly different phase
      > shift, each analog input has a slightly different phase shift, and
      > each sound card has a significantly different phase shift.
      >
      > My original SDR beam steering development system had an Athalon XP
      > 2000 or whatever processor, which is a single core, 1.5 GHz chip.
      > Even though there seemed to be plenty of CPU horsepower for DSP, one
      > Delta 1010LT would experience a "phase jump" with respect to the
      > other, from time to time. A good run would last a few minutes.
      >
      > I got a newer motherboard with a duo core Intel chip running at 2.0
      > GHz. I also selected PCI slots so each Delta 1010LT has the exclusive
      > use of a single interrupt. I am also running the RT version of the
      > Linux kernel. Some say that the RT patches are no longer required,
      > but I have not tested that assertion. The newer mobo seems to
      > eliminate the sporadic phase jumps.
      >
      > However, the phase shift from one set of 4 channels (8 analog inputs)
      > to the other set of 4 channels varies from one startup to the next.
      > (A "startup" is an instance of starting JACK.) The amount of phase
      > shift varies widely, from essentially 0 degrees to more than 100
      > degrees, when measured with RF and local oscillator signals that
      > result in 25 kHz audio signals. Apparently, the phase shift varies
      > linearly with audio frequency, which means the phase shift is really a
      > time delay.
      >
      > For Pro Audio purposes, this phase shift is probably of no
      > consequence, but for beam forming, the phase shift must be known.
      >
      > As my research has progressed, I have developed the following
      > calibration strategy. The steps overall steps are: calibrate the
      > analog inputs, then calibrate the RF inputs, and finally calibrate the
      > antennas.
      >
      > First, one applies the same known audio signal to each of the N (in my
      > case, 8) analog inputs and measures the amplitude and phase of each
      > digital signal relative to one of the channels. Rather than move 8
      > sets of plugs and cables around, I apply the calibration signal
      > through 10k ohm resistors in parallel to the Softrock outputs. That
      > is, I soldered 10k 5% resistors (need to order some 1% resistors) to
      > the Delta side of the 0.1 uF coupling capacitors at the output of each
      > Softrock audio channel. I currently drive just the "Q" channels with
      > a signal generator. This step shows that the "mike" input channels
      > (first two channels of each 1010LT) have a 7 degree (at 25 kHz) phase
      > offset from the other channels. I don't know the sign because I'm
      > only driving the "Q" channels. This step also shows that the phase
      > offset from one card to the other varies from nearly zero (3 degrees
      > on a good day) to more than 90 degrees. Again, I don't know the sign,
      > and that thwarts my efforts.
      >
      > Second, I apply a known RF signal through a Mini-circuits 8-way
      > splitter to each of the SDR receivers simultaneously. If I subtract
      > out the analog input calibration factors, I find that properly
      > constructed Softrock equivalent receivers typically vary about 10
      > degrees at 25 kHz below the center frequency (1830 kHz and 1855 kHz in
      > my case), and vary about 10-15% in amplitude. By properly constructed
      > Softrock equivalent receivers, I mean that the front-end pass band
      > filter has been selected for "constant group delay" (read: phase
      > shift) across the pass band, and that all of the inductors have been
      > wound correctly. One or two turns count errors will not keep the
      > receiver from working, but it does contribute a considerable amount of
      > phase error. I also used 5% tolerance capacitors, and I measured all
      > of the inductors, and selected inductors that were within 5% of a
      > nominal value.
      >
      > Third, I apply a known RF signal to the whole array. If I subtract
      > out the analog input calibration factors, and the receiver calibration
      > factors, I find that K7TJR Hi-Z active antennas typically have a 3-5%
      > variation in phase and very little variation in amplitude. I apply a
      > known signal by tuning the AM broadcast band during the middle of the
      > daytime when propagation is almost exclusively ground wave and tune to
      > a couple or 3 strong stations in the upper end of the band. Since I
      > know the location of transmitter, courtesy of the FCC database, I can
      > calculate the phase offset relative to one of the antennas of all of
      > the others based on the bearing to the station. A caveat: because I
      > can't choose the frequency of the AM station, and because I'm too lazy
      > to change my center frequencies (I use 1355, 1455, 1555 and 1655 kHz),
      > I am no longer consistently applying a 25 kHz audio signal.
      >
      > So, one those days that I get lucky, and I fire up my beam forming
      > software, and the analog input calibration shows both cards within a
      > few degrees of each other, then I can use over-the-air radio stations
      > to calibrate my circular phased array. The one day when everything
      > came together properly, I was able to find a pair of reversed
      > feedlines, and another feedline that was 14 feet too short, which
      > translated to a 10 degree phase error for that element. When all of
      > the errors are corrected, and I remove all of my Beverage wires from
      > the vicinity of the phased array verticals, then I can measure the
      > bearing to strong AM radio stations to within a couple of degrees.
      >
      > The next step is to use a couple of analog outputs so that I can
      > generate quadrature phased audio signals, and calibrate the analog
      > inputs using both the I and Q channels so I know the sign of the phase
      > error. The next next step is to measure the phase error at several
      > frequencies to I can calculate the slope of the phase error "curve"
      > (hopefully, a nearly straight line).
      >
      > Note that the motivation of all of the work above is that circular
      > phased arrays, especially "superdirective" arrays require significantly
      > more precise element amplitude and phase coefficients than do linear
      > arrays. My 8 element linear array is very forgiving of error.
      >
      > BTW, I have no experience with the Delta 1010LTs on Windows, and I
      > have no experience with any other sound cards.
      >
      > Hopefully, this helps. Hopefully noone will be scared away by the
      > apparent complexity.
      >
      > Victor, K1LT
      >
      >
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