# Packet Radio at 100 miles [closed]

I am wanting to assemble a Packet Radio solution that will allow for packet radio transmission with a range of about 100 miles or better. I am not sure what band to use, what radio to use, what antenna to use, and what terminal node controller to use (I have looked at KWM-1200+ Wireless Modem but am unsure if this will meet my needs). Can any one point me in the right direction for a solid solution that will provide my range needs?

Thank you,

• You should specify exactly what it is that you're after. Emergency communications? A way to talk to your buddy 100 miles away? What makes you think you need "packet" rather than some other digital mode? Are you willing to use existing packet digipeaters? By the way, packet communications over 100 miles isn't nearly impossible as some have said, if you're willing to use digipeaters. – rclocher3 Apr 18 '17 at 2:03
• This can be done on 2m SSB with enough antenna gain. I used to have a simple array of two 8-element Quagi antennas, one at 70' and the other at 78'. With only about 250w, I regularly worked many other stations with similar antenna systems with 100% reliability over 125 miles away. Reception at each end was never marginal. And I did this almost daily for about 9 years. – Mike Waters Apr 18 '17 at 18:19
• Check this out. 304 KM range, 5 GHz, WiFi connection over water achieved 5 MBps. High altitudes on both ends: newatlas.com/go/7878 – SDsolar May 2 '17 at 6:00

If by "packet radio" you mean the common AX.25 kind used by APRS for example, you can probably forget about it. Otherwise you'll need to use HF, and also find an appropriate mode since there's nothing quite like packet on HF which works reasonably well.

A VHF or higher direct link will be difficult. The radio horizon in miles of an antenna at height h feet is approximately:

$$1.23 \cdot \sqrt{h}$$

You say you have a 100 ft tower on each end, so that's $2 \cdot 1.23 \cdot \sqrt{100} \approx 25$ miles. To make that work you'll need much taller towers, or perhaps you can place one or both of them on a mountain peak.

You might also see How do I make a RF propagation map for a repeater?

Alternately, you could have a number of intermediate stations relay the signal. For packet radio this is called a digipeater.

If you want a direct link, you'll have to resort to something fancier. Troposcatter would be fun, but we can probably rule that out due to the very high transmit power that would be required. A communications satellite would be too expensive.

So that means HF. At distances of 100 miles, NVIS propagation is a good bet. You can play with VOACAP to get some idea, but the strategy is probably 40 or 80 meters with a low dipole.

You can pretty reliably communicate at these distances with such a setup, but getting packet radio specifically to work will be difficult. Packet isn't a good modulation to start, and on HF it's even worse.

There are some people running packet on HF, mostly 20 meters. It runs at 300 baud, and if you ever try it you'll find somewhere between 70% and 100% of what you hear are retransmissions.

Of course this isn't HF's fault: it's just that packet is horrible. The FreeDV modem is a better example. It transmits a 1400 bit per second digital voice codec (Codec 2) with a reliability that's around the same as SSB. That means we can use the SSB mode in VOACAP to get some reliability prediction. For me looks like with a 100W transmitter and a good dipole, about 90% is achievable at night, and 60% during the day. With better antennas, more power, or a lower bitrate, you can get those numbers higher.

Of course you want to send data, not digital voice, so you'd either need to use the FreeDV modem but send something other than Codec 2 over it, or find some other mode. There are plenty of HF data modes, but none of them are quite like packet.

• The question really is whether OP needs a kind of a broadcast or mesh system, or needs a uni- or bidirectional transceiver system; I'm absolutely not sure what OP needs from the question, other that it's data in packets :) I'd agree, 100 miles (assuming imperial units, that's 160km) for VHF/UHF will be pretty hard – path loss isn't your friend here, and neither is earth curvature. Troposcatter is weather and space-weather dependent – hence also my question (below SDsolar's answer) for reliability requirements... – Marcus Müller Apr 18 '17 at 8:29

That is a pretty good distance. There are a lot of factors that need to be considered.

First, do you have good tall towers on both ends?

Second, do you have somebody on the other end who will help you do this?

Third, is this for emergency services or something like that where it needs 100% reliability?

Then of course, why not use the Internet? It sure would be less expensive.

• I have a 100 ft tower available for the antenna, not sure what type of antenna to go with though. The receiving end will have the same. I will be able to control both ends. I just need to figure out what I need at both ends. This solution does need to be reliable. – Mike Z Apr 17 '17 at 17:41
• I am searching and searching and coming up dry on the reliability factor, even for just basic AX.25 messaging on 2m. It really seems that the Internet is your best option. – SDsolar Apr 17 '17 at 18:12
• Is there a shorter distance that is reliable? – Mike Z Apr 17 '17 at 18:30
• @MikeZ you can make even longer distances "reliable", but that a) depends on your very definition of reliability (these really mean very different things for different people), b) on the speed you need to achieve – making something that works 99.99999% of the time is a lot easier if you just need to transmit 10 bit per second, not 100 Megabit per second, c) on the transmit power you can spend (things will be more reliable with better SNR at the receiver) and d) the transceivers you can afford.... – Marcus Müller Apr 17 '17 at 19:38
• @MikeZ you should look at writing a proper specification of what you need. And then looking at what you can build. So far, you have not given a single "hard" number on anything, other than rate > 10b/s. Still no definition of maximum bit error rate, outage probability, max output power, min range... Way too many unknowns to suggest anything. Maybe: Write a question explaining what kind of thing you want to propose to whom, and ask for things that you want to specify. Maybe read up a bit on link budgets. – Marcus Müller Apr 17 '17 at 20:16

Take a look at this article. Radio communication via Near Vertical Incidence Skywave propagation: an overview. I'm not sure from my reading of the URL that the signals would make 100 miles. I understand the technique is being used in ARES where communications have been destroyed by a natural disaster. Article has some data transmission rates for various protocols.