Day Brown wrote: > Bob George wrote: >> How are you going to send data with this arrangement? > > I dunno yet, kinda expect someone will tell me how he's already done > it.
So YOU'RE not doing this then? > That chances that I mite stumble across something really useful that > has not already been done seems kinda remote. Actually, I don't agree. I keep bouncing responses back because I assume you are thinking about TRYING such a thing. I've been assuming you were doing something, but perhaps hadn't considered some aspect or another. > I dunno who National Semiconductor expected to sell their boards to. RF guys! :) Most CPU eval boards don't "do much" but an engineer can make them do something interesting for testing. However, that's usually as a proof of concept only, not a working unit. > I didnt see where the data that the board collected, actually was > ported to the ISA bus. Do you have the full link to the data sheets? The link provided didn't show anything. I'm curious to see what this is. > But one of the charts showed that one of the lines multiplexed two > 12bit data streams, so the sound card comes to mind. The 12 bits has potential (though I need to see that sheet) but: Aren't you trying to send DATA? If the board already multiplexes two 12 bit (digital) streams, you don't need to do any additional analog-digital conversion! It's DONE already! You just need to do something useful with that data once you receive it at the other end. > Stereo. Or are you trying to send a digitized audio stream? Voice-over-IP-over-Radio? > And it seemed that the com port (which we see dial up modems do > 4.3kb/second) But again... it's already taking a 12 bit stream, no? Does the board let you feed that via that com port, or is there some other data input? Your description has me thinking that's for control only, and NOT data to be sent. > could be used to adjust the transmit/receive frequencies by .05mhz in > a spread spectrum fashion that'd make detection, much less > interference, really unlikely in a wireless application. Well, sure but there's a problem. Someone has to RECEIVE that. Using a TV analogy, an appropriately equipped TV station could send snippets of over randomly changing channels. But if the receivers don't know what channel to turn to, they'll be lucky to catch the odd image. The "trick" of spread spectrum is in doing so IN A PREDICTABLE PATTERN. For any roll-your-own solution, you'd need to answer that puzzle. You could of course use the existing spread spectrum technologies adapted to other spectrum, but I suspect you'll find why it wasn't done using lower ranges. Your "chips" over a smaller range of frequencies for longer periods to transmit any data might not scale very well. > Since it only takes few bytes to change the setting, it could change > the tuned signals a thousand times a second. A possible problem with lower data rate/frequencies? > Scanners would never see it. Spread spectrum isn't hard to spot. To be useful, it has to be detectable! Of course, they may not CARE to. > They seem to be proud of their AGC capabilties, and if this is what > they mean, they should be. Since what you're describing doesn't exist, I doubt it is, and I doubt they are! > IIRC, a chart showed 3 more lines besides the multiplexed one, and > could use the others to look for noise free frequencies from 300 or > whatever mhz on down to DC. If they're digital input lines, how so? I'm not sure what you mean here. > The board seemed to be the size of a credit card, with only a few > chips; prolly sell for less than 10$. In QUANTITY (i.e. > 1,000) perhaps so. I'd be very surprised if they were that inexpensive in low quantities. > Aint nearly as complex as a cell phone. Probably don't do near as much either! > Seems to make sense that if you have a fixed desktop, you could run a > coax to an outside antenna, and have at least the range of a cell > phone for about the same money. So for the same money, what problem have you solved? Keeping in mind that the actual range of a cell phone is very limited (as opposed to the reach of the network it relies on) that's not much to brag about for an overly complicated system! I fail to see what this gains you that existing ham solutions don't. As a pure "hack factor", sure it's *interesting*. I once toyed with the idea of using the old, unused central intercom wire pairs strung throughout my (former) home as a crude data solution to network the house. I figured I could probably adapt something to let low-speed serial work over the speaker-type wire. BUT I realized it was something that would only be of use to me, would cost WAY more than was really necessary, and of course, it was completely obsolete by the time I was anywhere near ready to go with it. So if you're "Day"-dreaming, sure such things CAN be done. But I don't think there's a short-term solution to your data needs on the horizon. Now, part of my annoyance with you recently has been due to thinking you were really looking for answers, and not just "thinking via keyboard." Taking a MORE SERIOUS approach to your basic challenge: "How can I inexpensively send data to a neighbor located approx. 10 miles away with no direct line-of-sight?" and adding my own requirement for "legally and practially"... I've googled a bit, and I'm wondering if MURS may be what you need. Taking a look at: http://www.geocities.com/SiliconValley/Monitor/2254/radio2.html, I see: > The authorized bandwidth is 11.25 kHz on frequencies 151.820 MHz, > 151.880 MHz and 151.940 MHz. The authorized bandwidth is 12.5 kHz on > frequencies 154.570 and 154.600 kHz. [...] 1) You can transmit data > and imagery! 2) VHF is better for hooking up external antennas(less > feedline loss). 3) No license is required! Also, check out: http://www.guerrilla.net/reference/murs/murs.html > What makes this interesting is the possibility of using soundmodem > based utilities originally developed for ham radio use on the MURS > frequencies, for inexpensive data links over distances far in excess > of 802.11's capabilities. Unlike the ham bands, there will be no > restrictions on cryptography or transmission of commercial content. > While speeds are slow (9600 bps with soundcard based utilities, > higher speeds available with hardware solutions), we feel that this > is sufficient for many uses. So, what you're alluding to (complete with soundcard) IS doable WITH LEGAL FREQUENCIES, and products DO exist. Now, that IS slow stuff, but 9.6K can send a fair amount of email give a bit of extra time (recalling when 14.4Kbps was "HIGH SPEED") and if adding new techniques such as compression etc. then presumably effective rates could be higher. Day: If you're at all serious about this project, I'd suggest checking those pages for starting points. It sounds like you can (legally!) use existing, relatively low cost equipment to set up a point-to-point link to your neighbor with the high-speed Internet access, then set up communications between your house and his (hers?). Again, I don't use this stuff, so I'm not sure it's full-duplex (anyone?) If so, you can probably use existing software such as PPP together with a "modem" to transmit/receive. This may be IDEAL for what you've said you'd want: Namely the ability to send email back and forth to that neighbor. Two radios (plus antennas, towers as necessary) and a couple of old PCs, and I think you'd be in business! Now, I'm no ham nor communications expert, and there are some restrictions on use: http://wireless.fcc.gov/services/personal/murs/operations/ However, the basic challenge has been answered it seems. If you're just looking to "plug the computer into a radio", you need to solve the issue of channel contention/media access control. This was the basis for the precursor to ethernet: alohanet, which ran amongst the hawaiian islands. Another possibility would be to use SIMPLEX radios on different bands, still requiring some sort of coordination among them. Now, lest your rebel tendencies make you want to go stomp all over the FCC regulations and other legitimate users of these bands, take a look at: http://www.popularwireless.com/gmrsrhodeisland.html -- the story of how a pissed of citizen decided to hunt down a pirate user. While it's a different band with licensing, abuses CAN be hunted down by annoyed users. OK, so what you want to do CAN be done. I guess my question now is: Do you really WANT to do anything? - Bob
