1
$\begingroup$

My friends and I are going off to college ~180 miles/290 kilometres apart. As a project, we are looking into creating a data communication connection between our two schools. Our requirements would be:

  • 180 mile/290 km range
  • ~1 Mb/s connection speed both ways

Becoming licensed for amateur radio would be assumed in order to take advantage of lesser regulations/more frequency options.

Are there any technologies attainable at the enthusiast level that would offer these features?

$\endgroup$
  • 1
    $\begingroup$ Could you clarify your question to say if you need to use encryption or any other type of obscuring your communication for protecting against eavesdroppers, such a secret codes? If you do then that's a strict "no" for amateur radio. $\endgroup$ – Thomas Aug 26 '18 at 17:23
2
$\begingroup$

The most accessible way to get digital communication at that speed is WiFi. You could use unmodified consumer equipment, or getting a ham license would allow you to use frequencies not usually available to the public, as well as much higher limits on power and antenna gain. Of course the ham route would add additional restrictions, like it must be strictly non-commercial, and can't be encrypted.

Propagation at these frequencies for the most part requires line-of-sight, and 180 miles (290 kilometers) is too far on flat terrain. Even if you had a 100 meter tower at each end, you might get approximately 82 km. The general formula is:

$$ 4.12 \sqrt{h} $$

Where $h$ is the antenna height in meters, this gives the radio horizon in kilometers. The horizon distances from each end add together.

If the terrain isn't flat, and one or both ends is atop a hill or mountain, you can get more range. There are tools which can predict radio coverage. Unfortunately my favorite, CRC-COVWEB, seems to be defunct. You can also use HeyWhat'sThat just to check line of sight. It doesn't account for towers but it will show an elevation plan between two points, and then you can see how big the towers would need to be from that.

Another possibility is troposcatter, see Can tropospheric scatter effect be used by 802.11 links?

Or perhaps you can set up routers at intermediate points. This is an especially good option if there is a high vantage point visible from each of your respective schools. If so it's quite likely there's already a ham repeater(s) on it, and while they may not provide the data connectivity you seek, repeaters are often administered by a club. The club will likely be able to help you get access to the site, or at least introduce you to the right people.

If you can accept a much lower data rate, HF can reach 180 miles easily. However you won't be able to attain more than a few kilobits per second.

$\endgroup$
  • 1
    $\begingroup$ Below 28MHz, you're legally limited to 300bps (97.307(f)(3)). $\endgroup$ – Duston Aug 17 '18 at 15:01
  • 1
    $\begingroup$ @Duston That only applies to the lower portion of each band, and the "b" is for baud, not bit. $\endgroup$ – Phil Frost - W8II Aug 17 '18 at 16:29
  • $\begingroup$ Right, it only applies to the lower portion of each band because the lower portion of each band is the only place where data transmissions are permitted. (97.305) And I realize that "B" is "Baud" and not "Bit", I'm just skeptical that you can get "a couple kilobits" out of 300 baud. $\endgroup$ – Duston Aug 17 '18 at 16:50
  • 1
    $\begingroup$ 2000 bits/sec requires only 6.6 bits per symbol. For a relatively short-range, high-SNR link I don't see it wouldn't be attainable with modern techniques like QAM, OFDM, and spatial multiplexing. $\endgroup$ – Phil Frost - W8II Aug 17 '18 at 17:44
  • 1
    $\begingroup$ Pactor III can achieve 2700 bps over HF links; the details are here: arrl.org/pactor-iii $\endgroup$ – AA6YQ Oct 10 '18 at 6:34
2
$\begingroup$

In a word, No. For 1Mb/s you'd need a line-of-sight connection, so over a 180-mile path, you would need multiple hops. The alternative would be satellite communications but the ham satellites have neither that kind of throughput nor are geostationary (meaning you'd get at best a few minutes of connectivity per pass). Voice communication would be possible, as would low speed (300bps) data communication. And even if you did, there'd be no guarantee of privacy.

$\endgroup$
0
$\begingroup$

I think one thing overlooked here is the practical logistics of operating Ham radio from a University. Having done so at U. Central Florida, I can attest that one must be part of an Amateur Radio Club on campus which has a fixed station set up with antennas suitable for your purposes. If the equipment and logistics do not exist, they must be "created" and financed in some way.

Student government usually holds the purse strings for major club purchases. Thus you would have to provide a compelling reason for the university to purchase equipment necessary to create these links from school to school and also offer some public benefit for the expenditure.

If you and your friends are all Engineering students perhaps the College of Engineering might find Amateur Radio a good teaching tool and could supply the necessary resources as part of independent study.

Truly the most difficult part of this quest is the antenna(s).

In the meantime, using radio for basic email type communications is as easy as a local WINLINK system to inject your messages into an internet backbone to get them the rest of the distance to your friends via radio on the other end. While not strictly radio to radio, the experiences are invaluable and keep your comms away from the school's email servers. Not a bad benefit on it's own. ;)

Be creative in your quest!!!

$\endgroup$
  • $\begingroup$ I operated a ham radio station on campus at Oregon State University and I was never a part of a Amateur Radio Club. My station consisted of my Eico 720 transmitter, Hammarlund HQ-170AC Receiver, Home-brew 250 watt linear (dual-811 tubes), and Home-brew power supply for said linear. And, a 20-meter dipole antenna 5 feet above the roofline of the fraternity but it was a very big 4 story building (old southern style mansion type place). About 1966. $\endgroup$ – K7PEH Aug 26 '18 at 23:36
  • $\begingroup$ And probably very against school policy (it certainly would be in 2018). It was my intention to advise along these lines to avoid a student having to have a "run-in" with the school officials. Plus with a club, you learn more, help one another and are not an island. $\endgroup$ – guitarpicva Sep 13 '18 at 17:45
  • $\begingroup$ Seriously doubt that there were school rules regarding ham radio stations in Fraternities -- this was mid-1960s remember when you could ride your bike or motorcycle without a helmet and many other rules and restrictions of today were unknown at that time. Actually, my station was the 3rd or 4th that I knew of that used the same 20 meter dipole up on the roof. I think that dipole was installed sometime in the mid-1950s so it was 10 years old by the time I used it. $\endgroup$ – K7PEH Sep 13 '18 at 20:44
  • $\begingroup$ I suppose now they'd throw you in jail for RF exposure limit violations. Good times. $\endgroup$ – guitarpicva Sep 19 '18 at 0:44

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.