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.

Nothing amazing here

[Anonymous Coward]

Amateur radio operators have been doing this for years. The higher the antenna, the better. Put up a tower, say 50-60ft, put the antenna on top using good feedline and fittings, and you will get out to good distances. Better yet, take your laptop up to a mountain location, and you will be able to tx and rx for easily many times that distance. Hams do this routinely.

Re:Nothing amazing here

[dougmc]

But only with a license.

Yes, but it's not hard to get one.

I'm assuming they're unlicensed.

Well, they're likely FCC certified, but the spectrum they use is unlicensed, so ...

Obviously there are, but what are those limits?

For most of the unlicensed bands, under 1 watt. The WiFi `shootouts' and the like typically do not use amplifiers at all (microwave amplifiers are expensive), just high gain antennas, though I don't think the Part 15 rules (which is what things like this and WiFi are allowed under) allow the use of high gain antennas for transmitting. (If correct, this is very often violated, though obviously the FCC doesn't care that much.)

As for encryption, it's only the ham rules (part 97) that prohibit encryption. They also require that you ID yourself at the end of each message (and at least every 10 minutes) and that the usage be non-commercial. The FCC itself doesn't frown upon encryption, at least not publically.

I guess I need to read up on my FCC rules

Yup. This link might be an interesting place to start.

it's 900MHz

[Koyaanisqatsi]

40 miles alone is not impressive, HAMs talk all over the world on less than a watt (QRP) routinely, on HF bands off-course

But than I read this modem works on 900MHz, so that's quite a feat, worthy of a "Pringles can award"

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 ).