Saturday, April 11, 2009

Text Messaging and D-Star

I've mentioned a few times that its a bummer that the radios don't do this since 1200 baud is reserved for slow speed data.

After further research, the IC-92AD HT that I have been considering does do it. The messages have to be preset as a sort of quick text. It will store 6 messages of up to 20 characters each, which can be selected to be sent.

The ID-800 mobile works similarly. It will store 6 messages of up to 20 characters each, which can be selected to be sent each time you key the radio. When received, the message will (SLOWLY!) scroll across the display on the ID-800.

Editing these messages is a royal pain, because (of course) the radios have no keyboard.

The IC-92AD also has a kind of cool built-in voice recorder function.

The built-in voice recorder records an incoming (directed to your callsign) call for up to 30-seconds (approx.), (or 15 sec. × 2 tracks, 10 sec. × 3 tracks). For automated outgoing calls, you can pre-record up to 10 seconds of your callsign and/or CQ message in the IC-92ADs voice memory.

This functions of the callsign squelch. Out side of the DVR mode, you can set the call sign squelch function to only open the squelch only when your callsign is received.

There is also a break-in function built into this that allows a user to break into a conversation, where 2 stations are using Call Sign Squelch. The breaking station should enter the call sign of one of the stations they wish to communicate with. When you call the desired station, only the selected station will hear the call. With the break-in communication function enabled, both stations will be able to hear the call.

D-STAR also has "EMR" mode, (Emergency" mode), that was the engineer's obvious intention -- it opens all monitoring radios and even turns most models volume up to 50% if they were turned down, in order to get your call heard.

Sunday, April 5, 2009

D-Star data port?

I almost bought the IC-92AD at AES superfest. I had planned on it actually until I discovered a design flaw.

Apparently there a number of people reporting that the display goes blank after VHF transmit in DV mode. So something isn't shielded the best. Icom will fix this is you discover it and send it in. But that's just a bummer when you drop cash to buy a new radio only to have to send it in.

What did pique my interest for a while was the 12 pin connector on the handheld. There is an optional (overpriced) GPS speaker mike that interfaces to this port.

I knew it was wishful thinking that there might be access to the raw (signed 16-bit, Little-Endian, 8kHz, non-stereo audio packets.) AMBE decoded audio. Such is not the case. The 12 pin port is solely for the utterly useless slow speed data and some cloning functions.

Why anyone would bother with a 1200 baud digital data port is beyond me. We had that kind of speed with packet in the 80's. It makes sense to use that reserved 1200 baud for on-board text messaging. Or with that crazy priced GPS mic.

So it makes sense me to me that hams might want to interface to the digital audio part and callsign routing to try and create a SIP bridge.

Anyway you can't get at that DV stream which is a shame. So to experiment with interfacing a D-Star radio to Asterisk you really need to buy that overpriced DV-Dongle. Which of course lacks an over the air demodulator so you need to connect it to an analog radio.

What a bunch of bull.. D-Star isn't for me yet. I have other things to spend my money on, and there really isn't anyone around my neck of the woods with a D-Star radio. But it is interesting to read up on and play with some of the software being developed. Perhaps one day there will be such a standardized port, much like the standardized packet radio data port.

Above is a block diagram of how a D-Star radio works. As you can see analog microphone audio hits a single-channel, Analog Devices Front-End Speech Processor. This is actually what does the analog to digital and digital to analog conversion.

From there we have a RAW digital audio stream to the AMBE-2020 vocoder. This raw stream is signed 16-bit, Little-Endian, 8kHz, non-stereo audio packets. At this point this raw stream is a non-license encumbered codec, close in resemblance to ulaw (g711). The Linux SoX tool can convert most file formats, like WAV or MP3 to this RAW format.

The AMBE-2020 Vocoder Chip is configured to transmit and receive digitized speech to and from most linear, a-law, or u-law A/D-D/A codecs though its serial interface.

It kind of bugs me that there isn't a way to interface to this digital audio. I guess it's not a super big issue on a user end radio as you can always interface analog using the speaker microphone jacks.

Saturday, April 4, 2009

Wisconsin Amateur Radio Club - Digital Backbone Project

I spotted this at Amateur Electronics Superfest. Their demo was a pair of IP phones interconnected via 2.4 GHz shotgun antennas.

They are deploying a 5.6-5.825 GHz high speed digital network in Southeast Wisconsin. They are using the Ubiquiti Bullet 5HP, a 1 watt 5 GHz capable transceiver.

Due to the 6-54 megabit bandwidth, multiple simultaneous communications can take place on a single channel. Any site can act as an intelligent digital repeater into the network and thereby expand the mesh...

Due to he 12 volt operation and the small, high gain antennas, a portable station can be quickly assembled in the field and added to the digital backbone network.

Field locations provide: VoIP telephone for command posts, real time high resolution video of conditions, e-mail and file transfers, extension of the digital network, and standard voice type QSO's.

You can view the overview handout of their digital backbone project here: