# At what radius can you send peer-to-peer text messages / SMS over ham radio ?

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1. Apr 4, 2012

### cave_cat

at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

suppose we have lots of people concentrated in a small area, like a college campus. Maybe a mile or so in diameter. We would like to set up a packet switched peer-to-peer SMS transmission using low cost long wave radio devices, without having a central "cell phone tower". I guess kind of like bluetooth P2P network, except over a more meaningful distance.

What would be the complexity factors to consider in such a system, both technical and regulatory?

What would be the likely maximum radius of the covered area? Could this work with radius of .5 mile? 1 mile? 200 meters perhaps? Is that radius also related to the typical radius of operation of modern police / dispatcher radios or is it an entirely separate issue because of the lack of the central "tower" antenna?

Would the radio devices in such P2P configuration expend significantly more energy than the cell phone with tower setup?

In terms of regulation, what is the typical transmission radius when personal radios stop being "toy" and start being government regulated?

2. Apr 4, 2012

### Staff: Mentor

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

To use the HAM radio bands, you need to get your HAM radio license. It's pretty easy to do, and relatively inexpensive. Entry level handheld radios start a bit under $200. You can use your laptop's sound card capability and such a radio to send "packet" HAM radio messages, which are basically text-based messages, rather than voice-based. More info on HAM radio is in my footer. You can use GMRS voice radios, which require a very simple FCC license, but the range is probably too limited for most campus applications. BTW, with HAM radios and a system called WINLINK, you can couple your HAM messages to other operators using Internet-based repeaters, so you can basically talk all around the world. 3. Apr 4, 2012 ### cave_cat Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? berkeman, thank you for your response. Unfortunately, it seems that you have not really addressed the question of radius achievable for P2P packet switched radio network using quasi cell phone type devices. I also think that perhaps the discussion of "ham radio" is derailing us into an area that is unrelated to the short distance P2P interaction, so maybe that was the wrong word choice on my part. My goal here is to discuss low cost P2P communication in a small area as opposed to long range ham radio communication. 4. Apr 4, 2012 ### skeptic2 Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? That sounds like an interesting idea. You really need to give us more information in order for us to help you. What kinds of data are you planning to send and what speed do you need to send it at? Is it a college campus or "like" a college campus? Buildings have a penetration loss factor that varies greatly depending on the type of building. Going from building to building or within a building would have much less range than outdoors. What kinds of transmitters and receivers have you already considered? 5. Apr 4, 2012 ### cave_cat Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? skeptic2, the main application I am considering is relatively short text messages, sort of like "SMS" or "IM chat". The implication is that the sending and receiving bandwidth requirements for any given user are fairly low. On the other hand, we might want to support a lot of (let's say a few hundreds or even around a thousand) concurrent users of whom maybe around 50 will be actually transmitting at any given time. I.e. this is definitely not a high intensity application. In terms of the terrain, let's consider a flat plaza type terrain, without any serious buildings. So that could be a city plaza, a flat 3rd world village or something of that nature - I am guessing that this would be the ideal setup for this. I have not really "considered" anything in terms of gadget specifics because this is not my area of specialty. I can understand this stuff in terms of "what's the cost?", "what's the radius?" and other such functional questions, but for the insight/analysis of how such things could be realized given existing (or easy to make) radio gadgets it would be nice to get input from people who know this stuff. 6. Apr 4, 2012 ### skeptic2 Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? The fifty simultaneous users is the problem and I know of no off the shelf units that could do it. 7. Apr 4, 2012 ### berkeman ### Staff: Mentor Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? Can you just do it by writing a smartphone app? What parts would you not be able to do with that approach? 8. Apr 4, 2012 ### cave_cat Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? skeptic2, what about 50 simultaneous users is so complicated? Note that this is not a fully connected graph, i.e. every user will not be chatting with the other 49. More like with another 2 or 3 at worst. Further, since this is packet switched network, it can be implemented using ethernet type algorithm for handling collisions even within the same transmission band. Do you have any thoughts about the radius issue? What types of devices for short range transmission are available, and what are their pros and cons in terms of radius, cost etc? Further, if no low cost devices of this nature now exist, could they be designed and produced? E.g. if somebody designed a$20 cell phone for interacting with cell phone tower, could we design a $20 P2P sms sending device that I described upthread? 9. Apr 4, 2012 ### davenn Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? you are really leading everyone astray... we need some specific definitions from you firstly you want to about this in relation to using Ham radio. then you said you didnt then you state that you may have up to 1000 users of which maybe 50 are in simultaneous use. Then you say no its only 50 and maybe 2 or 3 simultaneous connections you keep changing the playing conditions. as for comms coverage, that depends on several things choice of freq transmitter power receiver sensitivity antenna type and gain local terrain they have to work over ( including building obstructions) as with skeptic2, I also know of no handheld (small portable) style system off the shelf that could handle this. the closest I could think of would be a WiFi net using wifi apps in mobile phones, Ipads etc Most wifi gear is going to have pretty short range, a few 10's of metres at the most and although you can get a wifi hub with respectable output power that may easily cover a say 200m radius, you Ipad or phone may hear that signal, BUT you are still limited by the TX power of the handheld device and its inability to get back into the hub receiver. And there's not a lot you can do about that. Wifi by definition is short range and low power. cheers Dave 10. Apr 4, 2012 ### cave_cat Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? davenn, I am not leading anybody astray. I am clarifying my thoughts as they emerge in the discussion with skeptic2. If I use some terms incorrectly due to ignorance, I am always ready to stand corrected. There is no contradiction between 1000 users and 50 users. 1000 users are like 1000 machines connected to ethernet LAN. 50 users are like 50 machines that are transmitting packets at some given time over this LAN. I understood the point about no off-the-shelf gadget being available for what I am describing. So, let's switch gears and talk about what is achievable in principle to put this into practice. What would be the requirements for such a transmitter in terms of the frequency? What range should we expect to get for various possible frequencies that could be used, within the overall limits of the problem I have described? Are there some frequencies (within this context) for which transmitter could be particularly inexpensive? In other words, what are the trade-offs having to do with frequency, range and cost that would determine the space of possible solutions? 11. Apr 5, 2012 ### skeptic2 Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"? If up to 50 users will be concurrently using the system, the main issue as I see it will be the talk to listen ratio. Collisions will necessitate the retransmission of both packets so they will up the Tx/Rx ratio. The Tx/Rx ratio will define the number of users on the system and vice versa. Exceeding either number will cause the system to crash. How would you handle that? You can't use 27 MHz citizens band (part 95) because data transmissions are prohibited, however you may be able to use 100 mW walkie talkies on the same frequencies because they come under part 15. FRS radios are out because the regulations don't permit data. The only other band that I think might work would be 902 to 928 MHz. Provided you use either frequency hopping or CDMA, I think you're permitted up to 1 watt without a license. Higher frequencies penetrate buildings better but are attenuated more by foliage. With a license, there are a lot more possibilities. Be prepared to pay$500+ for most licenses.

12. Apr 5, 2012

### cave_cat

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

skeptic2, I appreciate the points you bring up about packet collision and government regulations.

Now, can we backtrack for a second and discuss the range/technology/cost issue without these limitations? Suppose we have the ideal case of only 2 users at any given time, so no collisions. Suppose we don't have government regulators anywhere near us (maybe we ran away to Mars). In this hyper simplified case what kind of transmitter principles could we use, for the various ranges I suggested (200 meters, 800 meters, 1600 meters)? What would be the likely cost for such gadgets in mass production? Heck, what would be the cost for such a gadget if it were made from off-the-shelf components over at university EE lab?

13. Apr 5, 2012

### skeptic2

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

That is a question for you to answer not me.

14. Apr 5, 2012

### cave_cat

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

do you think that my last question is somehow improperly formulated? Or do you lack sufficient understanding of the short range radio transmission topic to attempt an answer to at least the first part, i.e. what device we would likely need and not how much it would cost?

15. Apr 5, 2012

### skeptic2

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

Your question is impossible for me to answer because I don't know any of the parameters of the radios. To begin to estimate the cost, you'll need to have a parts list which means the transceivers will need to be almost completely designed. Then there's labor. How can I even estimate what labor will be? Furthermore, for part 15 devices I believe the FCC allows you to make and use up to 5 units without having to get them certified (Who do you think pays for that?)

16. Apr 5, 2012

### cave_cat

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

yes, I understood that you cannot estimate cost. Sorry about the inappropriate question.

For now let's forget about specific costs, only keeping them in mind to filter out pointlessly expensive and hence absurd variants, along the lines of "radio with antenna of silver instead of copper".

Can you give any thoughts about the technical parameters of the radios in the ideal scenario (no regulations, only 2 users to avoid collisions, flat terrain) for the ranges like 200m, 400m, 800m, 1600m? As you have correctly pointed out in the previous post, the analysis must indeed begin from the technical parameters; and only once that is established it makes sense to study costs for achieving them.

17. Apr 5, 2012

### skeptic2

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

No, I can't.

18. Apr 5, 2012

### cave_cat

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

that's fine. Hopefully, at some point somebody else will :)

19. Apr 5, 2012

### Kurinn

Re: at what radius can you send peer-to-peer text messages / SMS over "ham radio"?

You could always use optical line-of-sight repeaters to cross longer distances where you can't get the power you would need for RF due to licensing or other considerations. Lasers aren't that expensive these days, although I'd imagine you'd have to design/build your own transceivers. I've never messed with modulating laser beams, but it sounds fun. Some commercially available drivers for diode lasers will accept external modulation, even if this is not their original purpose. The only boring part might be aligning your transceivers.