On 2011-04-28 20:49, Joseph Apuzzo wrote:
As some of you know I WAS a ham ( KD4HLC look it up ) and back in the early 90's (1992-3) mucked around with a 2400 baud Packet Radio ( on 2m / 70 cm ) Well that was almost 20 years ago and it seems that nothing has happened? packet radio is still around 2400 to 9600 baud?
On 2 meters (144 - 148 MHz for those who don't know what the 2m wavelength means) the baud rate is limited to 1200 baud, IIRC because anything faster won't fit in a normal FM channel. On 70cm (also called "432" because the center frequency is around 432 Mhz) I think a faster baud rate might be allowed, but I'm not positive -- I remember using 1200 baud on 70cm also, and remember that speed being typical.
Also for those who aren't familiar with "Packet Radio", those baud rates are for HALF DUPLEX transmission, and transmissions are packetized and NONCONTINUOUS, so you only get 1200 baud typically at about maybe 30% duty cycle. Not speedy.
Can anyone help me re-connect with my roots? 1) What is the modern hardware? That is what is the current "high speed" data transmission also on what frequencies?
Somewhere around 70cm and above is where baud rates are allowed to be over 1200 baud, but it's also more rare for hams to operate at the higher frequencies, and the higher frequencies also need higher antenna gain and thus narrower antenna beam widths (because gain=more narrow). So for instance if you're willing to go all the way up to 10 GHz you can transmit fast, but it'll require a dish antenna with a 2 or 3 degree beam width, which makes aiming two antennas from a distance at each other difficult.
2) What are the distances between nodes on the mesh? I know that frequency determines that, but hay my mind is not what it use to be some 20 years ago.
Distance = antenna gain and antenna HEIGHT. Height is a bigger factor than most people realize, because if at all possible you want line-of-sight between transmitting stations, otherwise the transmission multi-path can distort the audio and thus the packet transmission.
Similar to how repeaters are used for voice there are "digipeaters" to extend packet transmissions as much as 30 miles on 2m. There are also internet links between digipeaters, so for instance I used to talk over packet to people in London pretty often because of that.
But realistically packet radio (last I used it, anyway) was popular enough that even with just a portable "handy talkie", a laptop, and a small TNC were enough to connect to at least a few packet nodes and do things. Some TNCs come with message "mail boxes" so you can leave a ham a message in his TNC and a light blinks to let the ham know that he's got a "mail" waiting for retrieval out of the box.
3) Are there any really cool DYI modems that pair up with Linux BBS like software? Like http://dangerousprototypes.com/2011/01/31/packet-radio-and-the-arduino-radio-shield/
I build a DYI modem for a C64 "back in the day", and I still have a PK-232 MBX TNC that I've been meaning to fire up again sometime. Just... haven't done it.
3b) What is APRS? It sounds cool, but what's the down low? ( aka is it cool enough for me to want to get my ticket back? )
APRS is essentially "GPS for hams". Most hams use it for tracking their loved ones driving in their car. These days APRS is also used for the high-altitude balloon launches that have gotten popular to take pictures of near-space. Pretty good solution, except that the APRS modems typically have to be ordered pre-programmed with call letters. Some APRS modems are more easily re-programmed than others; the cheap, small, and low power ones I've seen are pre-programmed and then require JTAG to reprogram.
I haven't gotten into APRS myself but I get asked about it in relation to balloon launches often enough.
I can google some terms up and see that Amateurs transmit cell tower parts lists via digital transmissions at the first stage of a disaster but that's all. Where does one look for current info, and more importantly who can give a really good talk on the subject?
APRS comes up in the #lilug channel on irc.freenode.net often enough that I'd ask there first. I certainly KNEW enough about it at least at one time that I could give a talk on it, but of course I'd probably want to dust-off my TNC and get back up-to-speed before doing so.
One of the things I used to be involved in with Linux was building kernels with Packet Radio support on Slackware for a guy that built ROSE back-end trunking nodes. The nodes would operate at 1200 baud on 2m but would trunk data on 70cm at a faster baud rate between nodes using K2RIW 432 "Yagi" antennas that I supplied him after hurricane Gloria brought down an array of 16 RIW Yagis to the ground with a big smush because a tree branch rammed the side of the tower and sling-shot the array parts off the top. Look up those call letters, and you'll see something interesting.
-- -- Chris, KB2IQN -- Chris Knadle [email protected] _______________________________________________ Mid-Hudson Valley Linux Users Group http://mhvlug.org http://mhvlug.org/cgi-bin/mailman/listinfo/mhvlug Upcoming Meetings (6pm - 8pm) MHVLS Auditorium May 4 - Inkscape Jun 1 - Zimbra Jul 6 - Jul 2011
