Thursday, 6 February 2014

Notes from the Shack - February 2014

I was going to write about some complex logging software topics this month, which I'm sure everyone was looking forward to, but the arrival of a little device based on an Realtek RTL2832u chip changed my mind. I purchased the device from NooElec in the US for $17.95, plus $4 shipping (although I will confess to buying a bunch of accessories as well, more on that in another post), and it arrived at my office less than two weeks later. I have since seen similar units for less than $15 with free shipping to Canada. It looks like a large USB memory stick but has an antenna port on the side and comes with a small vertical antenna and a remote control.

The chip was designed for consumer use in Asia for receiving digital TV broadcasts on a computer supporting both demodulation and the USB interface. It is useless for that application in North America as we use different standards, but the same device works great as a simple Software Defined Radio receiver for approximately 25-1750 MHz.

Setup had a few tricks. I found the information I needed on the web which included using a non-standard USB device driver. The trick for that is to disconnect the computer from the Internet during installation so that the standard driver isn't automatically installed. If the standard driver is installed accidentally then it can be removed using the Windows control panel.

Just before I left work on January 29th, I downloaded everything I needed and on the train ride home everything was installed and working, including my long time favourite SDR program, HDSDR. On the way home I tuned in some mobile radio (couldn't tell who it was) and Pearson approach control. The next morning I was listening to local FM stations (the FM bandwidth is variable from 192KHz to 0), VE3YRC repeater and 2m, a local 6m repeater, and the Toronto Island Airport control tower. Not bad from the aisle seat of the GO train using a 4" long antenna and my shoulder as a ground plane.

If your transceiver has an IF output and upconverts to a high frequency IF (i.e. more than 25MHz) you can use the device plus software as a low cost panadapter. If, like mine, your transceiver has a lower IF frequency then there are inexpensive upconverting devices based on an open source hardware design available that will bring the IF frequency into an appropriate frequency range, as well as designs available for DIY on the web. The Ham-It-Up and the like can of course also serve as a standalone MF/HF receiver.

HDSDR went into a bit of frenzy when I accidentally tuned it out of the range of the RTL2832u (0 Hz, actually). I sent a report to the program's author, Mario, in Germany and within an hour or two he replied suggesting I install a different DLL to control the local oscillator frequency which fixed the problem. Other than that, there are no serious problems with the program or the device.



Steve VA3SRV has also been using something similar with the SDR# program. I noticed on the NooElec web site that a download package for SDR# and all the required drivers is available as a single ZIP file, which should make installation even easier.

From Steve's experience and observations of my own I wonder how many images I'm seeing. For $17.95 you're not getting a professional grade communications receiver and poor image rejection is a known "feature" of the device. A broadcast FM station was showing up quite strongly in the 10 metre band, for instance, and I see all kinds of signals in the 2m metre band, although those might explain why I see frequent desensing on my HF rig as they are very strong. In fact, this gadget may help me get to the bottom of the various RFI problems I see on HF.

This screen shot shows CHFI coming in a bit weakly.



HDSDR will display between 100Khz and 3MHz of spectrum centered around the frequency you choose. The entire 10m band can be viewed at once, for instance, or most of the 6 or 2 metre bands. It handles AM (including single sideband phase-locked to the AM carrier), FM, SSB and CW demodulation. With a virtual audio cable (or by feeding the demodulated audio output into another computer) it will drive all the various digital mode programs around, like MMTTY, FLDIGI, DM780 and FreeDV.

If you're looking for a way to tune in the 6 metre net, this little device will do just fine, attached to a suitable antenna for your QTH. It will also work with the 1.25m, 70cm, 33cm and 23cm bands, plus a whole lot more. If you want an way to try out SDR software without having to make a big investment it is also for you. Pretty good value for the cost of a couple of pints.

73,
Chris VE3NRT




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