Hi as I am new I dont know where to place this question.  There are 2 choice for telemetry (as I know) 900MHz and 2.4 GHz .

What are their difference (usage/setting) pro & con please. I saw they have same price.

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If you live in Europe you have to choose the 2.4 GHz version, check the open frequencies in your country. I'm not an expert on the telemetry module but with the same TX power 900 MHz has better range than 2.4 GHz. I know that for the European zone there is this module: XBee-PRO 868 but I don't know too much about it.

This fellow does a great overview of FPV, best camera, frequency and antenna, etc.

http://vimeo.com/user2797372/videos/sort:date

What Marc said. plus 2.4 gets blocked easier by objects in LOS, but that is secondary to another issue. If you use RC on 2.4, adding a noisy local transmitter to your rx on the aircraft will not improve, and is likely to hurt, your RC range and signal quality, even if the rx is SS, less so if it is good FHSS or DSSS, etc, and more so if it is poorly implemented. If you have the option in your region, I'd recommend the 900Mhz over the 2.4, which is really a bit less than 900, I believe.

I have to disagree with you Mike :), my store was the first to stock and release the 2.4 GHz telemetry kits, I had done a lot of testing on the telemetry kits before I released them here in the UK & EU markets, they have no more effect than two or more people using 2.4 GHz radios side by side, they were lab tested, real world tested and with my Futaba 7c I was able to go more than a mile away with a solid lock on the RX/TX. Please see the blogs linked below on the 2.4 and 868 xbees for more information.

 

http://diydrones.com/profiles/blogs/uk-eu-2-4-ghz-telemetry-kit

 

http://diydrones.com/profiles/blogs/xbee-868-revived

 

However I do agree on the range, the 900's are much better for distance, but here in the UK and many other parts of the world you have to fly LOS, less than 500 meters, the range I have with the kits I sell do that with ease, and a little more if you can't judge 500 meters so well :)

 

Regards

 

Martin

 

www.buildyourowndrone.co.uk

Agree with Martin, 2.4 telemetry and RC seem to work fine together (I fly Spektrum).

Not as scientific testing as Martin but never had any practical issues with my EZ* or quad

Paul

Ditto here. I've never noticed any hint of a glitch in more than 20 flights. Using Martins 2.4GHz XBee with a Spectrum module in a JR 9XII.

900 MHz is not an alternative in Europe, it is a cell phone frequency and you might experience a very uncomfortable surprise when they have triangulated the interference to your favorite flight location. 

868 MHz is also not a practical option due to regulatory and technical limitations that have been discussed at length in this forum.

Futaba and Spectrum are both known for good spread spectrum 2.4Ghz implementations. For cheaper implementations (I should say poorer, not cheaper) the results are a mixed bag. If the bandwidth overlaps for part of all of the signal, a 2.4Ghz transmitter inches from your rx will step on the signal from the tx. So there are a lot of "if"s there....

 

Given that most, if not all, rc gear in the 2.4 is using at least an attempt at SS, I would tend to believe that noticeable impact is very rare... but break out a signal analyzer and we might see that it is having an impact. 

Hopefully it does not affect anyone. The point of my recommendation is the same, if you have the option, I would go for the 900, not because of the potential for interference, but because the properties of a signal at 900 megahertz is that it generally punches through to your AC better, where as higher frequency gets blocked easier for the same power level by the moisture in tree leaves, by LOS obstructions, etc.

 

 

See http://www.rcmodelreviews.com/spreadspectrumtests.shtml for some videos on how various 2.4Ghz RC gear varies in its "quality" of implementing spread spectrum, and why some are far less tolerant of interference.... It makes things pretty clear, I think, when you see how the signal is put out across the frequency.

 

Radio signals are a bit like gravity... the closer it is, the more powerful, by a disproportionate amount. So if you are unlucky enough to have an RX that needs the same airwaves that your telemetry is kicking out just inches away, it will not hear part of your TX signal. Fortunately, SS is specifically intended to avoid this problem. Unfortunately, not all TXs implemented SS well. See the videos, it is pretty plain.

oh, and I think you are *far* less likely to run into problems w/ xbee, since it also uses DSSS, and a fairly good implementation. More likely to run into trouble between poor DSSS RC and a 2.4 video transmitter.

or a video transmitter and the xbee. Anything that dumps all of the signal in one wide portion of the spectrum, really, can degrade something else that uses the spectrum, even if you don't notice it, generally

You are correct on the RC TX/RX and video, I did find out a huge amount while researching the telemetry kit, like the DSSS which I had no idea about before I started to put the kit together, one point of interest on the video on 2.4 and the RC system running on the same band, Futaba state in their FAQ that they seen no issue running a 200mw video TX on a plane while using their RX/TX systems, that told me they have a great deal of confidence in the system not being blocked or upset with this power level and such a huge amount of information coming over the same band!

 

Futaba is very good; they are what I use. I am very happy with them.

I have lots of (non-RC) transmitters of all kinds, but nothing ever causes my futabas any problems.

 

73

KG4SEN

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