One-Watt Wireless Radio Modem Reaches 40 Miles

maxstreampr wrote in to plug their radio modem. It's the size of a credit card, one watt, and can transmit 40 miles line of sight or 3000 feet indoors. Something about using the AT command set to fire off a command 40 miles through the air amuses me.

Comments

Not very impressive

[jandrese]

Wow, that's some marketing. The "40 miles" claim is when you're in deep space and using high gain antennas. Actual performance will be less than a mile. Also, in case people want to compare this with 802.11 (which is difficult because they are in different bands), a typical 802.11b card radiates 30mW, instead of the 1W these guys are apparently claiming. The data rate is nothing exceptional either, 115.2kbps (and these are 1000 bits/kb sized), which pales in comparison to 802.11g at ~55000kbps. This technology would have a much higher "wow" factor 5 years ago, but nowadays that kind of range for that kind of throughput just isn't all that new or special.

Re:What kind of antenna??

[YankeeInExile]

Do the math ...

Po = +30 dBm
path loss over 64km at 915 MHz: -130
Pr = -100 dBm ... let's see ... at 9600 bps it requires -103 so that gives you 3 dB of fade margin even with isotropic radiators.

Put a +6dBi yagi (I think that is the maximum allowed on ISM under Part 47 anyway) at each end and you've got 15dB of fade margin, which should give you a couple of orders of magnitude of BER performance (the datasheet was notably lacking a BER / EbNo chart ).