Saturday, October 23, 2010

Ham Radio Cellphone Network

I highly recommend this article to anyone, it really resonated with me. The article makes a good point that anyone can throw a wire into a tree and call CQ. But there was one key paragraph that sent my mind wondering. I quote:
Future developments in the non-amateur world of radio from that point included cellular technology and the transmission of higher speed data over the air. Commercial applications for broadcast radio and television have changed radically and now include the imposition of digital methods. Military applications for secure battlefield communication use satellite and terrestrial means like mesh networking for voice and data transmission. Our homes, restaurants and coffee shops are bathed in RF transmitted data that keep our mobile devices connected to the Internet.
 Sure, there's the High Speed MultiMedia HSMM experiments... although the working group for that has disappeared and the general attitude I see about it, over and over is that you can do more with Part15 than you can with the higher power afforded with part97. It's a shame really. I've also seen a couple rare web pages discussing experiments with DATV. Much to my surprise, the experimenters preferred DVB-S to ATSC.

I'm not saying that Ham Radio is completely irrelevant. There's a lot of focus on it's use in emergencies and getting ready to help out in a disaster. And that's great. We have digital modes that run with a soundcard interface on a computer and software defined radio. There is a fairly basic digital voice mode called D-star. That's the big developments lately. Other than that, operating is fairly much the same as it was 30 plus odd years ago.

Why not a Ham Radio Cellphone network? I did some searching and this is what I've come up with..
Okay, the article discusses the use of this stuff to "hack" people's cellphone connections and listen in to their traffic. It misses a point that is blindingly obvious to me.
  • European GSM cellphones have 900mhz as a band
  • American Ham operators have 900mhz as a band
  • Hardware exists to set up a homebrew cellphone base station
  • How cool would it be to set up a legal ham radio cellphone network!
KJ6GCG, Chris Paget, set up his system to demonstrate the vulnerabilities of the GSM system specifically by spoofing the network ID for an active carrier. It should be entirely possible to set up a "fake" carrier that will not interfere with any commercial one and run it on our 900mhz band. Possibly even restrict access to special SIM card programming that could be posted online for any Ham Radio Operator to access. GSM can be run without encryption entirely, it's another point that allowed Mr Paget to demonstrate the call recording. Running in this mode will avoid any trouble with the regulations on the merits of codes and cyphers. The 900mhz band in the phones should be completely unused in America, that option is there to remain compatible with European networks.

Imagine this: Your area sets up a Ham Cellphone node and various operators get a GSM quadband phone of their choice (probably needs to be unlocked). Now they can carry a form of communication around that allows them to contact other hams at any time. It will always work in an emergency. You could potentially allow for a "phone patch" operation. It would be beyond easy to put in an extension number to allow access to any attached repeaters, echolink, etc. Call ex# 270 to access the 147.270 repeater!

I wonder if the data connection works.. Hello hinternet! GSM-APRS? Text messaging? You could set up a truely cell based network with HSMM backhauls between each cell. Put the backhaul in the Ham allocation of 2.4ghz and have fun.

The OpenBTS project is what makes all of this possible. They use a software defined radio called the Universal Software Radio Project (USRP) along with their own Linux-based software to fully act as a Cellphone Base station. There is a blog written by the OpenBTS developers here.

Incidentally, The OpenBTS people have been running a small cellphone network at the Burning Man festival for the past 3 years or so. They get a special temporary license from the FCC and coordinate it with the phone company that covers (or doesn't, in this case) the area. The Wikipedia article references this but I can't find the blog posts that I remember where they talked in detail about it. This is the authorization for 2008 with temporary callsign WD9XKN.

Of course, after writing this whole thing I run across a Wikipedia page with GSM frequencies worldwide. Some of the allocations fall in the 900mhz band but it's not clear to me if there are any channels that fall completely into the 902-928mhz bandwidth that we are allotted. Can uplink and downlink frequencies be set to fall within the allotment? Will that actually work with any phones? I don't know.

Questions? Comments? Flames? Does anyone really read these things?

Thursday, October 7, 2010

There have been a couple of interesting developments recently that I'd like to highlight.

The first one, I'm most excited about it, is the announcement of the SDR-Cube Transceiver.
A Portable Software Defined Radio
Utilizing An Embedded DSP Engine
for Quadrature Sampling Transceivers
George Heron, N2APB   and   Juha Niinikoski, OH2NLT
Very Neat! This kit takes a SoftRock 6.3 SDR and provides a dsPIC with all the brains to do AM/SSB/CW. It's apparently built to be very easy to couple with a NUE-PSK modem for not only computer-less SDR but PSK operation too. The makers say it can work with other computer coupled I/Q SDR boards as well, so it should work with any other SoftRock. The case will come painted black and several kit options will be available. They are planning to be a source for the SoftRock 6.3 RXTX if you want to go with that option. Personally I'd rather use an Ensemble RXTX and have 3 bands.
I highly recommend anyone to check out the website here.

NUE-PSK modem. I kinda wish they had a keyboard built-in. It'd look a lot like an old Tandy Model 100 though. That wouldn't be a bad thing, I don't think.

Something similar is the Mobo 4.3 Project. I don't know a whole lot about this project so I'll let the page speak for itself:
An all singing and all dancing all band 5W HF Software Defined Transceiver based on the popular Softrock 6.3 RxTx kit.
The Motherboard, or Mobo v.4.3 is an addon board to plug onto the Softrock v6.3 RxTx, to transform it into an all band (160-10m) HF SDR transceiver electronically controlled via USB.  This project, which started in mid 2009  has now been through the initial development phase, the result being a nicely performing all band transceiver, with an exceptionally linear transmitter output.  Measured IMDR is of the order of 48dB at 1W PEP and a respectable 31dB at 5W.  

Sounds pretty neat but again, with this project you require a PC to run the radio. Now if we could combine these two projects somehow, that'd be really neat. One thing that really impresses me is the digital power/swr meter. It's the smaller board to the right in the above picture. If the mainboard detects a high swr, it can automatically reduce your power so you don't burn out the driver. How cool is that?

Finally, Wouxun has announced a new radio in their line-up. It is a dual-band mobile radio. Link to the image, the Ed that runs has all the details. No pricing information on it yet.

  • Dual Receive (Truely, not dual-watch like the handhelds)
  • Crossband
  • Dual Frequency display
  • 50W
  • 999 channels
  • Remote head.. Mount radio somewhere else and just put the head on your dash. Looks like Mic plugs directly into the head also. Hope that's a standard feature and includes mounting gear.
Looks like there are going to be multiple versions like the handhelds. 218-260 is listed! So there's a possiblity there of 2m/222.. 136-174/218-260. There's also some weird stuff like the possibility of 2mhz-30mhz AM-only receive. Or 500-2000khz, Or 50-500khz all AM-only. I don't really see the point in it but there you go. Apparently FM broadcast is available too. So one option there gets you AM & FM radio. The 2-30mhz option is kinda pointless unless you want to listen to CB though!