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,
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.
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.
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.
