900MHz XBee

ajward

Anyone have experience with the 900MHz XBees? I'm trying to put together a remotely controlled 'Bot with a wireless camera, but both operate at 2.4GHz and simply don't like each other. The 'Bot will move and there's no video OR great video and the 'Bot refuses to move. Then, in the middle of it all, the router steps into the fray and neither of them work, plus there's no internet connection. I've tried changing channels on the devices, but haven't found a combination that works. At this point, I'm thinking the new XBees are probably a cheaper solution than a new wireless, rechargeable camera.

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Rforbes

Well, I use the 900 MHz XSC version. Shooting data down a mountain, through several multi-story buildings, 3 acres of trees, across a 4 lane highway, through more trees and a couple more buildings to the destination. Total distance is 0.92 miles. Average RSSI is around 27 decimal. A few packet losses here and there (about 1 in 1000) but no other problems. This application uses yagi antennas and isn't very data intensive- about 1kb of data per minute total, a portion thereof every couple seconds.
Love me some XSC action!

Duane Degn

Rforbes wrote: »

Well, I use the 900 MHz XSC version. Shooting data down a mountain, through several multi-story buildings, 3 acres of trees, across a 4 lane highway, through more trees and a couple more buildings to the destination. Total distance is 0.92 miles. Average RSSI is around 27 decimal. A few packet losses here and there (about 1 in 1000) but no other problems. This application uses yagi antennas and isn't very data intensive- about 1kb of data per minute total, a portion thereof every couple seconds.
Love me some XSC action!

This sounds so cool! I don't suppose you have a link to the yagi antenna you use?

@@ As I mentioned in the other XBee thread, I've used the XSC version too. I haven't done anything as cool as Rforbes has with mine but I did walk down the street to see how well the transmission was received. I had one wire antenna on one XBee and a "real" (antenna in black plastic case) antenna on the other XBee. The signal was pretty good about a block away but once I turned the corner placing about a dozen houses between the XBees, I lost the signal.

I'm pretty sure the general rule is you get greater range with lower frequency (using the same power) so 900MHz radios tend to have better range than 2.4GHz radios.

What transmission is more important to you, data or video? You might want whichever is more important to be the one switched to 900MHz. I've also heard 2.4GHz is really crowded with wireless keyboards, wireless mice, etc.

Rforbes

Duane,

You betcha. Here's the yagi. https://www.tessco.com/products/displayProductInfo.do?sku=85730

I use this omni on a 3rd base. https://www.tessco.com/products/displayProductInfo.do?sku=352355

These might not be great choices for a wireless bot.

Chris Savage

One thing I have noticed is that two radios that may otherwise work okay in the same environment don't do so well when they're very close to each other. 2.4 GHz band covers a range of frequencies and the radios shouldn't be on the exact same frequency, however they may be experiencing issues from being too close while in the same band.

extrabee

I've had really good luck with the 900 MHz XSC modules. Keep in mind there are two different versions with wildly different over-the-air data rates, and the lower speed one gets better range (though unless you're near the edge of it's capability, you may not notice the difference). I've done some pretty serious testing with them and found that setting the retries (or multi-transmit, if using broadcast addressing) high can get you about as much range as the slower module, but you'll still get less than full data throughput.

Chris also has a very good point, if multiple transceivers in the 2.4 GHz band are too close to each other, even if they are on different channels, the receiver becomes desensitized by the transmitter nearby (basically even though it's on another channel, it is so powerful that the low-noise amplifier in the receiver can become saturated and not pick up distant signals very well). CDMA cell phones actually have to deal with this constantly -- when you walk into a building, the cell phone immediately boosts it's output power because the tower needs all of it's received signals to be of similar strength (it's more complicated than this, but the concept still applies).

Good luck!
Jeremy
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