Short range radio link instead of cables.

[Rorshach]

Greetings Programs,

I have myself a small but hopefully good quandry. With some of my retro gear setup in different rooms I must find a way to link them so I can transfer programs between them. Dragging entire shelving units from one room to another will never happen so that is out As is wifi as none of these systems have ethernet either. What I need is a small radio based RS232 link I can use as I can use RS232 on my Retro gear. I have seen one company that offered 49mhz RS232 radio modem & transciever units available but I have not been able to order from them as they do not answer emails nor phone calls to get ordering & price information.

Another option I had considered is using 2m or 70cm HT's as I have a valid amateur radio licence but that would tie up all the equipment for my packet radio system I am setting up. Nor do I want local hams seeing the paswords & logins on my linux system as any encryption on the ham bands is strictly verboten.

What I would like to do is find some (probably industrial) data radio to go from my various 8bits in different rooms to my linux system which will host files to be downloaded & uploaded. Anyone know of a source for this sort of equipment? licencing is no problem as I can arrange such on my end.

[Paul]

One option may be to use traditional phone modems.  Many homes are wired with 4 wire telephone wire, but a single telephone line will traditionally use only two of the four wires.  The other two could be wired to a second jack (dual jack phone plates exist for this reason).  While you won't get the traditional dial tone, two computers can use this network to communicate with each other in your house by simply issuing an "ATO" command on the terminal computer and an "ATA" command on the host, using standard Hayes-compatible modems.  They will be able to communicate over this otherwise "Dead" line.

[Rorshach]

This won't work as theres no phone jacks anywhere near where the computers are hence the need for totally cable & wire free.

[MikeS]

Maybe you'll find some ideas here:

http://drvernacula.topcities.com/index.htm

[Rorshach]

Hi MikeS,

Some of these are promising. Most useful looking is the ones from Yishi at http://www.yishi.net.cn/index.asp?id=47 These are full transcievers that can be easily interfaced to RS232, basically just requiring the proper 9pin or 25pin connector. Only downside for me is these is they are at 433Mhz which is in the lower part of the Amateur radio 70cm band. Now that I think of it there is one other possible glitch, that is the dreaded secondary purpose in the 70cm band known as "radionavigation" which is typically radar. In 70cm band this is more typical in more northern parts of canada but can be picked up further south too and this could generate interferance.

Some of the other projects use seperate transmitter & reciever modules either on 315 or 433 mhz so a 2 modules would be required at each end and would need either both bands for full duplex or half duplex on single channel.  But it is doable. I will try contacting yishi to find some prices & ordering info and report back when I have further info.

[MikeS]

Why not send a note to James (address at bottom of page) - he experimented quite a bit and could probably give you some useful tips as well as price & ordering info for the Yishis.

Also some interesting stuff here:
http://www.sparkfun.com/commerce/categories.php?c=16

And some slightly more expensive stuff:
http://www.electronickits.com/kit/complete/complete.htm

Finally, if you've got a pair of modems and the room, folks have used old cordless phones...

m

[Rorshach]

MikeS,

There is a couple from Sparkfun that look good, support RS232 and are 2 way and give a choice of wifi or bluetooth among the other choices. The bluetooth option would be expensive at $82 each plus shipping and whatnot and needing one on each end. The wifi model could be a more useful choice for going through my wireless router and less expensive but limits options connecting two "retro" computers in different rooms directly. I'm looking at this one myself at the moment.

There was a chinese manufacturer that had a decent looking transciever module but they never answered my emails about availability and price so they have disqualified themselves.

The electronic kits RS232 are good for one way data acquisition links but are disqualified for my uses on several counts. The main problem is they are strictly one way only, either transmit or recieve but not both so I could be on one of my 8bits in one room and tell the other system to begin an file transfer but the other system could not send and my 8bit could not recieve.  The 433.92Mhz frequency also puts it right in the lower end of the 70cm band, which I use for amateur radio.