SparkFun Forums

[mike944]

Hi,

I'm interested in the UM96 433mhz long-range modem kit: https://www.sparkfun.com/products/155

I only need 1-way communication (simplex), but i need more range. I want to connect this to an amplifier. If i connect this to a conventional 1-way amplifier, I assume it will kill the 2-way capability, right?

My question is, does it need the 2-way capability for error correction? Basically,if i kill the 2-way capability, will it still work?

Thanks,
Mike

[stevech]

100mW is all you can get realistically in this band. To increase a bit more, use a yagi gain antenna. Power amps at this power level will likely violate FCC rules.

Any decent wireless system must be two-way.
Look at these mini-wireless boards w/radio, and look at the radio modules per se if you don't want the MCU+radio on one board.
Sorry, SFE has slim pickings
http://www.anarduino.com/miniwireless/

a 100mW radio (20dBm) will get line of sight 500m at low bit rates like 4Kbps. Range reduces as bit rate increases. Of course, adding a directional gain antenna helps a lot.

Don't waste time with the $3 on-off-keying (OOK) also known as ASK (amplitude keying). The radios above are frequency shift keying (FSK or GFSK) are two-way, have built in error detection. Error correction is done by ACKs and retransmissions done by higher level software such as
http://www.airspayce.com/mikem/arduino/RadioHead/

[mike944]

I'm having a tough time with this. My parameters are a bit too much. I'm trying to get serial telemetry data from a moving car, up to about 1 mile away to a stationary receiver. Directional antennas are not an option because the transmitter is moving. I only need like 9600 baud, and only 1-way. (I can drop error packets)

I'm trying to be self-contained, so trying to do it without cellular.

There are minor line-of-sight issues as well, so I was looking for some power.

I think I found a solution on ebay. Just got a good deal on a commercially produced solution, which can function with repeaters. 900mhz, 1 watt frequency-hopping, so it has power, and it's legal

[stevech]

1 mile range, moving car, etc.
It's hard with unlicensed band power limits.
Need 2 way for error correction.

Is the path always line of sight?

[mike944]

No, it's not always line of sight. That just adds to the problem. That's one of the reasons I was looking at a low-ish frequency, for slightly better propagation characteristics. I'd like to be legal, but....the track is in the middle of nowhere. If I was down to legal-ish emissions at the track property lines, I'd take the small risk. If I'm above legal power, I'll certainly investigate licensing.

That being said, I've realized that 433 is not in the ISM band in the US. Not sure the rules about sending data in the 70cm amatuer band.

Any idea on which bands will be licensable for data?

As I said, I just picked up 4 Freewave DGR-115 modems. Assuming they all work, or can be fixed, I can use 2 as repeaters, and that should work perfectly. It's also 2-way, so I'll have error correction