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DIY SDR In January 2013 QST

| homebrew, QST, SDR | January 2, 2013

The January 2013 edition of QST from the ARRL features, among other projects, an inexpensive SDR made with mainly off-the-shelf components.  I’ve been mildly intrigued by all this I-Q/quadrature/SDR nonsense and figured this was a low risk way to give the technology a try.

Following the guidance in the article, I found on ebay the needed DTV-B dongle and ended up paying less than $20 total for the item. The USB stick arrived the day before Christmas. I let it sit around for a few days before getting around to trying it out.

First things first, my goal was to get the TV stick working with the SDR software to receive VHF radio signals. I carefully followed the instructions to download and run the installer script which downloads and install all the software you need, from the replacement USB driver to the SDR client itself.

Installation was as smooth as silk, except for one problem…

It didn’t work!

The USB driver said it installed fine and all was A-OK. The SDR software fired up just fine. It’s just that the SDR software didn’t see the USB TV stick at all.

Ok, off to the forums. Time to re-install drivers. Verify that my USB hardware is in fact supported by the driver and SDR software, etc, etc. Nothing I tried seemed to help. The USB TV stick just wasn’t there according to SDRSharp.

On a hunch, I tried plugging the stick into a different USB port on my laptop. Restarted SDRSharp and voila! The USB TV stick was immediately recognized.

Not all USB ports are created equal!

I “tuned” the software to the FM broadcast band as I was sure to have lots of strong signals to test with there. Sure enough, the spectrum scope and waterfall display came alive with numerous signals and my speakers emitted the familiar sounds of FM radio. The SDRSharp software even decoded some of the encoded song information included with the main program signals.

I tried some copying some 2M amateur activity, some VHF marine channels and some AM aircraft band signals. It’s fun to watch signals popup on the spectrum scope and try to to tune-in on them by clicking on the signal. Kinda like playing radio whack-a-mole!

The next part of the project is to build an LO front end to block upconvert the HF spectrum to VHF where the SDR stick will act as IF and detector stage.

I have most of the parts needed, including a rather ancient NE602 mixer-oscillator chip. The only thing I don’t have is the 125Mhz xtal oscillator module.

This is a fun project and inexpensive way to dip your toes into the world of SDR. The QST article advertises “SDR for less than $50″, in fact you can do it for a lot less with some careful shopping on ebay and a moderately well stocked junk box.




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