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Open-Hardware Licensed Handheld Software-Defined Radio In the Works
An anonymous reader writes "Chris Testa recently presented at TAPR Digital Communications Conference and annouced his development work on a hand-held software defined radio. Running uClinux on an ARM Corex-M3 coupled to a Flash-based FPGA, it will be capable of receiving and transmitting from 100MHz to 1GHz. Designed to be low power, Chris has designed the radio primarily with the Amateur 2m and 70cm bands in mind. Currently in early prototyping stage, Chris intends to release the design under the TAPR Open Hardware License."
The only real limits are: RF front end/IF section (if any, could be a direct conversion) FPGA speed The latter really only comes into play for high datarate/frequency work, so its all in the (hopefully replaceable) front end.
But I don't know enough about designing this kind of thing to know if that is feasible.
The SDR is feasible, in fact, easier, but the problem is the "handheld" part -- "emphasis on the word, 'handheld.'" The physical size of the antenna starts becoming uncomfortably large as the frequency goes down -- or, said another way, the efficiency of the antenna goes down with frequency if the physical size is held constant. A full-size 50 MHz quarter-wave whip antenna is 1.5 meters (or metres, if you prefer; about 59 inches) long; that's pretty unwieldy for a handheld radio.
The 2 meter and 70cm bands are by far and away the most popular amateur radio bands, and they are the most accessible. All license tiers can use them, and equipment can be had for reasonable prices.
These sorts of considerations are very important if you want to kick off something you want to see widespread use. HF can always be added later, once a project develops traction.
I want! Imagine a mesh network of these, put the evil telco's out of business :)
Then if the future of 2m, 70cm is narrower channel bandwidth than is currently used (how could it not be given the public service channel bandwidth now used) the nice thing here is that you only have to install the ROM image with the new modulation, keeping the old bandwidth as a feature anyway. Leading to more space for local groups in the long term from free software. I'd bet the lack of 6m comes from one of the chips at the RF end being limited to 100MHz. It's quite easy to fill-in the 0-100MHz block for receive with a cheap mixer (see the article in this month's QST, pg 30 I think).
I just started using Gqrx and a rtl device for $20 to get started in software radio.
Grabbing the APT images from polar orbiting satellites.
http://www.oz9aec.net/index.php/gnu-radio/gnu-radio-blog/477-noaa-apt-reception-with-gqrx-and-rtlsdr
There is also the Funcube USB Dongle you can use but its more $$$$.
But is there any shortage of openly published and easily accessible hardware designs for amateur radio?
Found text link in the comments to the video:
http://blog.testa.co/
Yes. And if one makes a 6m antenna the same physical size as a handheld 2m antenna the 6m loading coil will be larger, its series resistance will be higher, and the 6m antenna will be significantly less efficient than the 2m antenna. It will work "well enough", for suitably generous definitions of "well enough."
The optimum operating frequency for a given service can be determined (in the absence of regulatory restrictions, of course) analytically, taking atmospheric noise, antenna performance, and receiver noise figure into account. See, for example, Kai Siwiak, Radiowave Propagation and Antennas for Personal Communications." Second Edition. Boston: Artech House. 1998. Chapter 4.7.
12 hours and only 37 comments? The response to a device like this should be far greater on a site like Slashdot. *Sigh*.
Anyway, I've always felt TAPR kits were not entirely within my grasp due to either high prices or high complexity. I hope this will be an affordable kit which doesn't require a ton of SMD soldering. Take the lead from Raspberry Pi - small, simple, affordable hardware.
Good luck! I'll see you guys at Dayton!
Chris Testa KD2BMH here. marid, your suspicion is correct, the CMX991 transceiver I'm using has a low-end cutoff of 100MHz.
The HF converter w/ a NE-602 mixer in the latest QST looks like an attractive solution to support the missing lower frequencies receive, I'm guessing 2 would allow me to build a full duplex transceiver.
I'm using a 40MHz ADC & DAC, so at least some of the HF bands should be possible using direct conversion.
Either way, HF wasn't part of my initial plan, I'm focusing on exactly what I can fit inside easily, and then more features can be added later. Launch & iterate... the kitchen sink will come in one of those iterations :)