Wednesday, February 29, 2012

472kHz I/Q-SDR kit

Nothing is for free, up to now, there is no kit available for 472kHz.
However, there is one for 136kHz, which can be easily modified to match the new band.
Check out box73's longwave I/Q-SDR kit.

You will see that a 15MHz signal is divided by 25. This results in a 600kHz signal which is further divded by 4 in order to create the phase shift. All in all, this ends up in a center frequency of 150kHz.

We can use the same oscillator and divide the signal by 8. This results in 1.875MHz, which will be further divided by 4 providing a center frequency of 468.75kHz.
With a sampling rate of mere 24kbps, or +/- 12kHz bandwidth, the entire band (472 to 479kHz) will be covered.

The digital part is rather simple to modify. A suitable ripple counter could be the 74HC93.
The frontend is even more simple... just pick a 455kHz i.f.-filter/transformer and replace C1, C2 and L1.

Should the old experimental range, somewhere above 500kHz, be a desired range, the additional modification would simply replacing the 15MHz canned oscillator with a 16MHz one.

I will see if I can persuade the OM at box73.de to provide such a kit.

2 comments:

  1. Just received an email from the box73 editorial board. It seems that there will be no 472kHz-SDR kits. It has been suggested to me to rather use the more expensive (and over engineered) FiFi-SDR.
    Well, I don't think so! In my opinion, the "Einsteiger SDR" will do the job for 472kHz just fine.
    In the view that 472-479kHz will be a world wide HAM radio band, not providing such a kit looks like a missed opportunity to me...

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  2. I just received a second mail from box73's editorial board. Now it seems that the idea is understood and taken into consideration. Hence, there seems to be a good chance that the kit actually will be issued.

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