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[Linrad] Re: Update on SDR-IQ + Linrad + MAP65
- Subject: [Linrad] Re: Update on SDR-IQ + Linrad + MAP65
- From: Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>
- Date: Thu, 13 Nov 2008 23:07:11 -0500
Many thanks for your note! I'll let you know when there's something
ready to test. You should be able to run it on a single (fast) computer.
Let's be sure to work on 2m this weekend! If you call CQ, I'll find you...
-- Joe, K1JT
Edward Cole wrote:
> At 07:54 AM 11/13/2008, you wrote:
>> Yesterday I spent some time playing with an SDR-IQ (from
>> RFSpace) on both HF and 2m EME. It is an impressive little
>> box: very simple, it just does what it is supposed to do.
>> It works fine with Linrad, as well as with the SpectraVue
>> software by AE4JY. Running the SDR-IQ under Linrad, I found
>> that 2m JT65 EME signals are easy to see on the waterfall.
>> I'm sure that none of this will surprise any reader of this
>> list who has already gained some experience with the SDR-IQ.
>> I have worked out, on paper, a scheme that should allow
>> MAP65 to work with an unmodified SDR-IQ running under
>> Linrad, while minimizing necessary changes to the MAP65
>> program code. The scheme involves choosing suitable
>> decimation parameters CIC2, CIC5, and RCF for the SDR-IQ
>> (these are parameters you can set from within Linrad) and
>> suitable lengths for the FFTs used in MAP65.
>> For your interest, here's a table showing some parameter
>> values in the present MAP65 (used with 96 kHz soundcard
>> input) and in the proposed "MAP65-IQ" as it would be
>> configured for the SDR-IQ:
>> Parameter Soundcard SDR-IQ
>> (MAP65) (MAP65-IQ)
>> f0 RF sample rate (Hz) - 66,666,667
>> nd Decimation factor - 714
>> CIC2 CIC5 RCF - 7 17 6
>> f1 Baseband sample rate (Hz) 96000.0 93370.68
>> n0 FFT for sync search 32768 32768
>> w0 Bin width (Hz) 2.930 2.849
>> n1 FFT full transmission 5,376,000 5,378,240
>> Factors 7 5^3 3 2^11 7^5 5 2^6
>> t1 Time for complex FFT (s) 1.39 0.66
>> n2 Inverse FFT, each signal 77175 79380
>> Factors 7^3 5^2 3^2 7^2 5 3^4 2^2
>> t2 Time for complex FFT (s) 0.00607 0.00324
>> f2 Final sample rate (Hz) 1378.125 1378.102
>> Both systems provide usable bandwidths of 85-90 kHz -- more
>> than enough to cover the relevant JT65 sub-bands for EME on
>> 144, 432, and 1296 MHz.
>> For each one-minute block of received data, MAP65 does 279
>> FFTs of length 32768 to get power spectra for all required
>> half-JT65-symbol intervals. The resulting (32768 x 279) 2-D
>> spectra are searched for JT65 sync signals and shorthand
>> messages. The slightly different bin widths w0 in standard
>> MAP65 and MAP65-IQ can be easily accommodated in the software.
>> MAP65 then does an FFT over the full span of received data
>> (about 52 seconds), with the complex data arrays zero-padded
>> to length n1. Inverse FFTs of length n2 are then done with
>> data around each frequency where a sync tone was found.
>> This process yields downsampled complex data with effective
>> sample rate f2=f1*n2/n1. As you can see in the table above,
>> the parameter values given in the MAP65-IQ column yield an
>> f2 with almost the same value as in the present version of
>> MAP65. This condition is desirable because it requires a
>> minimum of changes to the remaining downstream program code.
>> As shown in the table for both MAP65 and MAP65-IQ, the
>> selected values of n1 and n2 can be factored into a number
>> of small primes. This condition is necessary for the
>> efficient computation of FFTs. The FFT lengths for MAP65-IQ
>> are actually "better" than those in the present MAP65, in
>> that their FFTs run nearly twice as fast (see values of t1,
>> t2 in the table). Of course, since MAP65 operates on
>> dual-polarization data while MAP65-IQ processes a single
>> polarization, MAP65-IQ already has less than half the
>> computational load. MAP65 is fast enough on a modern
>> computer. MAP65-IQ will be several times faster.
>> MAP65-IQ should be an excellent tool for anyone using JT65
>> with a single-polarization (or switchable polarization)
>> receiving system on 144 and 432 MHz. It should also make a
>> superb JT65 system for 1296 MHz, where circular-polarization
>> EME is the norm.
>> I hope to find time to work on code for MAP65-IQ over the
>> next few months.
>> -- 73, Joe, K1JT
> Thanks very much for working on this. I will try this out with my
> SDR-IQ and Linrad. I guess you are still running Linrad on a
> separate computer from MAP65 (or not). I have not gotten into the
> interfacing of Linrad to MAP65 since I was waiting for the SDR-IQ solution.
> Is there things to do to make Linrad talk to MAP65 in the above
> procedure? I can also run Linrad on the same 2.33 GHz computer If I
> can find out how they port together.
> 73, Ed - KL7UW BP40iq, 6m - 3cm
> 144-EME: FT-847, mgf-1801, 4x-xp20, 185w
> 1296-EME: DEMI-Xvtr, 0.30 dBNF, 4.9m dish, 60W (not QRV, yet)
> http://www.kl7uw.com AK VHF-Up Group
> NA Rep. for DUBUS: dubususa@xxxxxxxxxxx
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