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[Linrad] Re: Update on SDR-IQ + Linrad + MAP65
- Subject: [Linrad] Re: Update on SDR-IQ + Linrad + MAP65
- From: Edward Cole <acsalaska.net; kl7uw@xxxxxxxxxxxxxxxx>
- Date: Thu, 13 Nov 2008 19:03:32 -0900
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
>
Joe,
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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