I'm not sure if this should go here or on one of the electronics pages, please advise me if this is misplaced.

I work at a local hardware store, and I along with the other staff all agree that an internet connection would be extremely useful. Only issue is, my boss doesn't see the usefulness of it, and won't purchase broadband.

I had a random idea pop up in my head the other day when someone was talking to me about dial-up. That used sound over the phone line in order to create a connection. My first thought was that I could set up some kind of dial-up server at my home to share my internet connection with the shop, but that would cost a fortune in phone bills and both my house and the shop needs it's phone line open.

I found a few walkie-talkies in a cupboard in my house, which made me think, as the distance between the shop and my house is within the walkie-talkie's range, would it be possible to convert the data on my network into sound, transmit it across the walkie talkie to the shop over one pair, then visa versa in return?

I understand that the speed would be incredibly slow, but the main thing we would be using it for is email, so speed isn't all that important. But other than speed and the fact that I would have to actually make it, is there anything else in the way of me doing this?

Also, if this is a possibility, what would be the most efficient way of sending the data. My idea at current involves compressing the data, encrypting it, and transmitting the binary data for that in 2 pitches (high = 1, low = 0), however I understand that that only allows me one channel of communication. 7

I have a fairly decent knowledge of both programming and electronics, but networking is a bit beyond me.

Thanks in advance for any answers :)

  • That would possibly be illegal, at least it would be in the U.S., for frequencies which walkie-talkies use.
    – Ron Maupin
    Apr 9 '16 at 21:12
  • en.wikipedia.org/wiki/Amateur_radio You should start by finding your local amateur radio (ham) club.[www.arrl.org] Btw, there are off-the-shelf radios that can do all this crap for you. Also, your walkies are half-duplex
    – Ricky
    Apr 9 '16 at 22:49
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 14 '17 at 1:44

This is absolutely possible, but it will be much slower than you think. Your assumption that you can use a modem to convert data into an anolog sound signal and transmit it over the walkie talkie is correct. See this modem that I designed exactly for that purpose: http://unsigned.io/projects/micromodem/

The problem is that the speed of such a modem is only 1200 bits per second. And you simply wont get much more than that over a walkie-talkie audio link. For an in-depth explanation of this, have a look at this post I wrote to someone else about the limits of walkie-talkie data rates: http://unsigned.io/forum/viewtopic.php?id=48 (the explanation is the second post in the thread)

If you really want to do this over RF, you should use a modern wireless bridge running in the 5GHz band for example. There is many on the market, and I use one particular brand myself extensively in my work to set up wireless connections like the one you are talking about with distances anywhere from a few hundred meters to several kilometers. The speeds you can get on these can easily reach hundreds of megabits, but does require proper installation, alignment and configuration.

So in short, while it is possible to do what you want with a pair of walkie talkies, speed would simply be too slow. You can get other gear for the task that is specifically suited to actual internet connections.

  • You can only get 1200 bps if you use the full range of sounds available over a phone line.. The simple high/low sound idea would me much slower.
    – Ron Maupin
    Apr 9 '16 at 21:18
  • Thank you for your answer. To be completely honest this was more of a fun project than a final solution anyway. I just wanted to see if it would work at all, and if it did work okay then I have a solution. I had overestimated the speed at which this would work. Playing out the hypothetical here, with all OFCOM regulations aside, someone in this thread stated that by using FM, you have the potential to send 1Mbps, are they right? reddit.com/r/askscience/comments/24z54c/… Apr 9 '16 at 21:30
  • Without doing the actual calculations, 1Mbps on a standard FM broadcast radio channel sounds about right, but that's using a modern modulation technique like QAM, and with more RF bandwidth available. If you read that post I linked to, you can get an understanding of why those things matter (and you would be able to calculate it yourself as well!). But an audio-coupled transmission line over a pair of walkie talkies is something completely different :) Much less bandwidth, and you need to use a modulation scheme that can pass through an AC-coupled circuit.
    – Mark Qvist
    Apr 9 '16 at 22:42
  • @RonMaupin, that you need to "use the full range of sounds" available on a phone line to get 1200 bps is not true. You should have a look at any of the standard AFSK 1200bps implementations available. Having both designed and built several 1200bps AFSK modems myself, I can attest that using a two-tone system like AFSK effectively gives you 1200bps over radio, or a phone line. Actually that modem does 2400bps over a phone line with the same two-tone AFSK system (phone lines are generally less distorted and noisy than an RF channel).
    – Mark Qvist
    Apr 9 '16 at 22:46
  • @RonMaupin, if in doubt, you can build one yourself and try it out :) Both the hardware and software of my design is open source and easy to put together on a breadboard.
    – Mark Qvist
    Apr 9 '16 at 22:49

You have broadband in your pocket (your 4g LTE Smartphone). Have a look at WiFi tethering - your carrier may or may not charge a fee to enable it.

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