Developers Disclose Schematics For 50-1000 MHz Software-Defined Transceiver

Bruce Perens writes Chris Testa KD2BMH and I have been working for years on a software-defined transceiver that would be FCC-legal and could communicate using essentially any mode and protocol up to 1 MHz wide on frequencies between 50 and 1000 MHz. It's been discussed here before, most recently when Chris taught gate-array programming in Python. We are about to submit the third generation of the design for PCB fabrication, and hope that this version will be salable as a "developer board" and later as a packaged walkie-talkie, mobile, and base station. This radio is unique in that it uses your smartphone for the GUI, uses apps to provide communication modes, contains an on-board FLASH-based gate-array and a ucLinux system. We intend to go for FSF "Respects Your Freedom" certification for the device. My slide show contains 20 pages of schematics and is full of ham jargon ("HT" means "handi-talkie", an old Motorola product name and the hams word for "walkie talkie") but many non-hams should be able to parse it with some help from search engines. Bruce Perens K6BP

Comments

Re:Bruce, finally something worth while

[Bruce Perens]

My pleasure. We have a lot of fun with this stuff, and I'll continue to try to stretch the envelope for as long as I can. Chris and I have talked about doing an open-bitstream gate-array after this project.

Many are leaving ham radio too

[Anonymous Coward]

I spend several years of my life helping to get rid of the Morse Code test for radio hams, so that smart folks like you could just take technical tests to get the license.

Actually, many "smart folks like us" obtained amateur radio licenses only to leave the hobby in dismay after a decade or two. Hitting one's head against restrictive regulations just became too painful, especially the disallowing of encryption and content restrictions on carrying Internet traffic.

Until a few decades ago, an amateur license provided the operator with abilities which were totally unavailable to the unlicensed man in the street. That situation has reversed dramatically now. Wifi and cellphones far outperform almost all forms of digital communication available to the radio amateur, and they provide near-total freedom of content.

It's a very sad state of affairs, and what makes it even sadder is that the majority of old hams are in denial that this even matters. "No freedom of RF speech and we love it that way" seems to be the most common attitude among old timers. Well that just doesn't work for the younger generation who love RF but want it to be useful as well.

Today's youngsters are born into a world where the Internet is as fundamental as running water, and this places high expectations on amateur radio. It is expected to provide useful communications, not just a quaint technical passtime. "Useful" is defined by comparison to what they already have and use in their daily lives without needing a license.

The telephone shaped today's amateur radio regulations, and that antiquity shows. As a result, today's road to amateur radio is a two-way street, as not everyone stays in the hobby once it becomes clear that the old regulations are hostile to normal Internet communications. The rules are deliberately disempowering to the license holder, for whom a comms link that is not allowed to carry Internet traffic is, in 2015, about as useful as a bicycle to a fish.

Re:Many are leaving ham radio too

[Bruce Perens]

Actually, I led the fight to continue to disallow encryption on the Amateur bands just last year. I evangelized a lot of people to comment in opposition, and even dragged a reluctant ARRL into commenting when their original intent was not to do so. You'll notice that I am cited in the FCC ruling. It was only proposed to allow it for emergency communications, anyway.

You already have many different radio services where encryption is allowed. The shared, self-regulating nature of Amateur Radio makes encryption a disaster, as does the international nature. You can't self-regulate when you can't understand their communications. Nobody wants to see dxpeditions and HF communicators in general treated as spies by various nations, more than they already are.

We're perfectly happy with how useful Amateur Radio is, and it is not denial. Use the Internet and other services when you need encryption.

Re:50 Mhz lower limit? Ouch.

[fyngyrz]

What's the point of a fancy SDR on the lower bands though? At least in the States most of the amateur bands with any kind of useful propagation are so narrow that one of the brain dead simple sound card SDR rigs can cover the majority of your band of choice.

This is going to be long-winded; there's quite a bit to cover. Sorry. :)

Cover, yes. Cover well, no. You need lots of bit depth for adequate dynamic range without filters, bit depth almost no one offers, and if you don't have adequate bit depth, then you really need front end filtering and probably a stepped attenuator as well. You need EM protection because HF antennas tend to be large and prone to large induced voltages. You need good frequency linearity if you want to use the SDR to get accurate measurements (even the s-meter.) For the ham bands, it's also nice if the SDR supports a sample rate of 400 khz or better, which is tough for a sound card SDR. Then there is frequency accuracy and stability, not to mention external reference sources (there all kinds of cool things you can do with a very stable SDR, like this AM graveyard band carrier forest), and then we get into multiple front ends for diversity reception and noise reduction. If you want to remote the SDR for any reason, you really need ethernet, and if you need ethernet, you need some smarts. And you need ethernet anyway, because USB bloody sucks (speaking as a cross-platform developer.) So If you want a good SDR, you just don't end up with a "brain dead simple" SDR.

As to narrow ham bands in the HF range, well, not really. 160 meters is 200 kHz. 80 meters is 500 kHz. 20 meters is 350 KHz. 15 meters is 450 kHz. 10 meters is 1.7 MHz. The WARC bands are all pretty tiny. Also, for SWL, some of those are quite wide, and even more so if you include the out of band regions where the pirates are. Pirates being quite unpredictable, you want them in the spectrum so you can see them when they pop up, so bandwidth is quite relevant if they are of interest (personally, I find them fascinating.) Come to that, if you want to see what overall prop/activity is looking like, you need 30 MHz of bandwidth to do it live.

I will grant you that someday, we may be able to put a 48 bit, multiple Gs/s A/D on a chip with a full ethernet interface cheap enough for anyone to own; but not right now. Until that day, good SDRs will not be "brain dead simple."

More on frequency range: If you want to use the SDR for a panadaptor for an existing receiver (very common use), then it has to cover one of the IF frequencies and associated bandwidth of the receiver, which tends to be in the HF range (not always, though.) Then there are cray-cray folk like myself; among other things, I use my SDR to monitor bats in our attic. To do that, the SDR has to be able to do a good job with the first 100 KHz, also true of experimentation with sonar and other audio ranging and detecting tech.

I'm not saying there isn't stuff up higher than HF; of course there is. Some of the really cool stuff (wifi, for instance) is as high as 5 GHz. Satellites, public utilities, etc. Any motion video needs to be up pretty high (but it also needs very significant bandwidth.) But HF has a huge amount of interest, it's where most hams actually hang out, and as it's a very challenging reception environment, higher end designs are of great interest. So are hackable designs one can get at. For instance, if you built yourself a multi-stage filter bank for the various HF bands, you could have them switch automatically as you tune. Likewise you could control add-on attenuators, RF preamps, and switchable transverters (which can give a nominally lower freq range SDR excellent access to higher bands.)

I have a variety of SDRs, and switching is simply a matter of prodding a menu. I have access from about 1 Hz to 3 GHz across the group, with varying features as described above. In the end,

Re:Unlike copyrights, patents expire.

[Bruce Perens]

The first-use-in-commerce date is actually earlier than the date on the patents. Thus, the patent would not be expired, but could no longer be enforced.