a_majoor said:
Asking for a range of 60 Km is a bit much for a single radio set, unless it is attached to a honking amplifier and a gigantic mast. For practical purposes the long range will have to be passed on to an RRB, a radio relay UAV, an aerostat (tethered balloon or blimp) or sent via Iridium or IMERSAT.
It's funny, I started thinking about a UHF radio with a whip antenna tethered to a balloon while browsing through this thread... it's actually an extremely viable idea, just not practical considersing the availability of the INMARSAT, particularly considering the current INMARSAT (Which costs somthing along the lines of $12-15 per minute) is being replaced by the Ottercom Storm ($0.89 per minute) and the troops in afghanistan will shortly be recieving Harris Multiband FALCON II radios, capable of a variety of comms, including HF, VHF and UHF, and supposedly are capable of sattelite comms while on the move.
Col Banks wrote an article in the CAJ 8.3 regarding the American Task Forces in Afghanistan, one thing he noted was that sections could be from 5-30 Km from the Platoon; and the Platoon HQ was often 30+ Km from the Coy HQ. Given the distance and broken nature of the terrain any VHF solution will have a great deal of difficulty, and I wonder if HF would be viable given the combination of radio waves bouncing off the unstable atmosphere and the small receiver "targets" deep in the valleys. Maybe we need to move into Iridium technology in a big way to support widely dispersed operations and overcome the effects of atmosphere and terrain.
I'm not sure how familiar you are with HF, it's definitly viable in this case, that's why we've got man-packs.. there are limitations though... I'll give a quick run-down of factors applicable in this situation...
HF signals travel in two ways (They do so simulatenously, it's just the nature of the wave). They produce a ground wave and a sky wave. The ground wave travels in a line along the ground, the same as a VHF wave. The sky wave travels up to the sky, bounces off the ionosphere, travels back to the ground, bounces off the ground and continues this cycle.
One major limitation with HF is that propgation (How well the wave travels) is poor at night, sometimes a frequency that works well during the day will not work at all at night (It's entirely possible to have no frequencies in your list of freqs that work), though this only applies to sky-waves, ground waves will still work. Ground waves are limited roughly to line of site (Not entirely true, but true enough).
That being said, the 138 man pack is capable of a slightly higher power out-put then the 522 manpacks, and as such, can push a ground wave further, so assuming you're in range of the ground wave, the above limitation is not always a problem.
Some HF freqs may also be in use elsewhere around the world, and because of the potential for global propogation of a signal, it's entirely possible other users may interfere (Translation: When we're working with HF, sometimes we'll hear foreign news, music, conversations, all sorts of strange things, even in the freqs assigned to us)
ALE (Automatic Link Establishment) overcomes some of these problems, by automatically selecting the best freq from a list of programmed freqs, but it's slow somtimes...
Most (All) strategic HF dets (Army dets, as well as naval ships) also use a sattelite backup (Often INMARSAT, don't know if there's still any heavy sattelite dets) in case HF means are unavailable, or for priority traffic.
A hand-held sat phone (I am sure there are some out there with embedded encryption, none in the system that I'm aware of, but there's plenty of stuff in the system I'm not aware of) and a 138 man-pack may be an option for patrols far from the CP, not always as quick as VHF comms, but still, it may be viable.
