3 ms·

Say you are just 1 mile from a friend, at 151Mhz the fresnel zone is 72ft tall. If you are both at equal elevation on flat land then 50% of the signal is going

Say you are just 1 mile from a friend, at 151Mhz the fresnel zone is 72ft tall. If you are both at equal elevation on flat land then 50% of the signal is going to be absorbed by the ground. How exactly does this scenario work? Source: I used to build outdoor medium distance (~1mi) wireless data networks with 900Mhz and at 1 mi the fresnel zone is roughly 30ft tall so we would put our antenna 20ft in the air. The awesome thing is we could shoot through a mile of forest but only if 60+% of the fresnel zone was not occluded by the ground. Edit: I should also add that I would have loved something like this in Iraq. Next to keeping soldiers fed, coordinating with adjacent units (read: not shooting at each other) on foot during a mission is about the biggest challenge there is.

TD-Linux 12y ago
The propagation characteristics of VHF are substantially better than 900MHz. I've used voice radios in the VHF band in urban Minneapolis, and have been able to easily surpass a mile of range. I'm surprised they didn't choose a lower frequency still. In addition, using something like DSSS, a low data rate, and retransmission ability will probably help a lot for this application.
- daniper 12y ago
  Agreed. Substantially better. Our first goTenna prototypes worked at 900 MHz band and we could barely get 0.5 km (NOT MILES) line of sight. With the goTennas that are now out for pre-order, we've gotten anywhere from 0.5 miles to 3.5 miles in NYC (where we're based), to give you an idea -- and there's little that is as non-ideal for RF propagation than a metropolitan city.