Thursday, February 21, 2013

Radio hacking: Baofeng UV-5R edition
This rather industrious individual has been working on replacing the main CPU in his Baofeng UV-5R transceiver. These are cheap radios of course, but one of the neatest things is that they are cheap partly because they have a lot of functionality integrated. If I understand it correctly, there's a chip that basically handles everything for the radio functionality and then you have a CPU that controls the whole shebang over an SPI interface. The radio chip is an RDA1846.
The RDA1846 is a highly integrated single-chip transceiver for Walkie Talkie applications. It totally realizes the translation from RF carrier to voice in the RX path and from voice to RF carrier in the TX path, requiring only one micro controller.

The RDA1846 has a powerful digital signal processor, which makes it have optimum voice quality, flexible function options, and robust performance under varying reception conditions.
 Cut the power to the main mpu and that frees up the bus to communicate with the radio chip. In Lior's case, the SPI connection became damaged so he was able to enable I2C mode. He is using an Arduino so it actually works out to be easier to interface.

One neat thing he's already discovered is the ability to direct the RDA chip to produce sinewaves at any audio frequency and here his is demonstrating that by transmitting his callsign in morse code. According to him, 1200 baud FSK is even possible. That's just cool.

He has a page available here:
This has more information and he may also work on the Baofeng UV3R at some point.

Incidentally in the discussion somehow a link to a bluetooth module was posted: It'd be really neat to integrate a bluetooth module into something like this in order to use a cellphone bluetooth headset on a radio, but this one seems to be specifically for stereo bluetooth speakers. I wish someone would make a more universal module that could provide one or two or no serial profiles, one or two or no headset profiles, stereo profile, so on and then you could use whatever you needed in the project.

Tuesday, February 5, 2013

Codec2, wifi and the future of Ham Radio

I've been keeping an eye on the progress of codec2 more recently. There's a modem and mode for using codec2 over the air now. FreeDV is a modem for Windows and Linux that lets you send codec2 voice in a 1.1khz bandwidth that can be sent over FM or SSB. The codec runs at 1400bps in this mode and has room for a callsign ID in the stream. Very neat!
I'm hoping sometime this year I can get one or two Raspberry Pi boards and configure it with one of the Debian distributions as a standalone codec2 digital radio, using standard 2m radios for the RF. Who knows, maybe I can use the GPIO pins with my reverse engineering work from last year to allow it to completely control my TM-241a radio.
Codec2 can, of course, be run at several other bitrates and other modems. suggests that a GMSK or C4FM modem might be developed for FM use.

Last year at the Hamvention a SDR based data radio was announced that could do up to 56K on 440mhz. UDR56K-4, KB9MWR has the press release. What I find interesting is that you could fit many streams of Codec2 audio over a 56K stream. What if you could get 2 pair of these modems, 2 inexpensive duplexers and then have a "wide" (for Ham Radio) bandwidth full-duplex link into a disaster area? You could have some bandwidth set aside for a dozen or more VOIP telephone links, compressed with codec2, for people to call out on. Meanwhile have bandwidth left over for emails, forms, graphics, you name it.

Another interesting thing that is going on are these little pocket sized wifi APs from China sold under the TP-Link name. You can find the TP703N for $20 on eBay practically any time. They have a port of openwrt, there are other devices available if you browse through that page. This particular one has 1 ethernet port, 1 usb port, 1 usb power in (5v 500ma) and of course built in wifi. Probably ideal for a HSMM-Mesh network. Thanks to the openwrt port, it should be possible to make these mesh nodes, or even more easily enough. I don't think they use the full 500ma so a small power source might be enough to keep one running for quite a while depending on what it is.

A lot of work has been put into smartphone technology in the commercial sector over the last decade, it'd be great if we could use some of that. A part15 wifi mesh would be nice in an emergency area. Non-hams could connect to it with their smartphones and get necessary information in several forms. Maybe apps could be developed which would let people send small messages, their GPS location or maybe a compressed picture to people who could use that information to direct personnel. As a part15 network, it wouldn't be necessary to worry about restricting who can use the network or if any traffic might pass over it that would violate part97 rules.

The FCC is trying to free up more spectrum for free wifi usage. This article has the idea that they want to act as an ISP, but that's not what I understand. From what I understand they just want to open more spectrum up like the 2.4ghz and 5ghz bands for wifi. This is contingent on TV broadcasters giving up some of their spectrum instead. This means it would be much lower frequency (under 900mhz, above 440mhz) which should help the signals cover more distance. I have to wonder what this will eventually mean for the Ham world above 30mhz. Maybe someone will make a 2-way radio that runs on super-wifi?

There are the Ubiquity and other branded* 440mhz wifi modules as well but I have not heard any reports on those. They are not cheap by today's rates. I think they were >$100 per module and then you still had to have something to put them in.

*I can't remember what other manufacturer was making these now and my Internet searches are inconclusive tonight.

Stumbled across this article about Hams using wifi which posits a 2.4ghz digital wifi repeater with a 25mile range. I'm going to read more of it later but that could be interesting. Obviously using pricier equipment than the TP-Link stuff.