Thursday, 14 May 2015

Parallel IF Code

The Parallel IF idea is getting an airing at QRP-ARCI's Four Days in May convention this week.

The Vero demonstrator has accompanied me across the pond and will be available for scrutiny at FDIM (and for demonstration, if we can cobble together an antenna and catch any signals)...

To celebrate and support the event, I've released a copy of the Parallel IF code, which is available at my Github repository. It is the same code as that running on the demo system above.

It is underpinned by the Si5351 device. Whilst my original Parallel IF rig used (and still uses) a pair of DDS modules, I'm not going to release any code for these AD9850 RF generators, believing the Si5351 to be the better choice for this application.

The core of the technique involves the establishment of a 2*2 MATRIX of local oscillator frequencies, where before there was just a two element vector...

One row of the matrix, indicated by a red box in the graphic above, is associated with each of the IF paths. In my case, there is a 10 MHz path, used for sideband applications and a 12 MHz path, used for CW applications. The particular frequencies in the matrix are associated with MY home-brewed IF filters. If you use the code, you'll need to change these frequency constants to suit YOUR filters!

The two columns of the matrix, indicated by the blue boxes in the graphic above, are associated with lower and upper sideband operation, respectively.

The code between the appropriate row, depending upon the user's choice of receiving bandwidth and the appropriate column, depending upon the band, to set the local oscillator (/BFO).

My presentation at FDIM presents the contrast in receiving response achieved by selection of one of the two parallel IF paths using a rather childish analogy with the width of an open door - the tight CW band presenting a narrow opening and the sideband channel giving a wider opportunity to pass the signal...

As ever, bug reports, comments etc., gratefully received!

...-.- de m0xpd

1 comment:

  1. Glad they got the live streaming working after lunch so I could see and hear your presentation. I have followed your blog for quite a while, and agree with you and Pete the si5351 is just great for what most of us are working on. I heard one of the last questions you were asked about making a stand alone version of your receiver evaluation system. I have a couple of SA604 ICs and am looking at "Philips Semiconductors Application note
    AN1991 Audio decibel level detector with meter driver" . This looks like it would make the AF measurement for your system. I am thinking of taking one of these and connecting to the my SNA JR and a little change in software and make a stand alone system.
    73 DuWayne KV4QB