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[Linrad] Re: Update on SDR-IQ + Linrad + MAP65

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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