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Old Apr 10, 2007, 05:56 AM
Rox
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6EX-2.4GHz system

Futaba has recently released 6EX-2.4GHz system with R606FS receiver which has two antennas ... with a requirement that the two antennas should be placed at 90 degrees to each other

First question: is that really necessary to shift to 2.4 GHz band rather than 72 MHz even most of the fields that I visit are not that much crowded!!!

Second: Having TWO sensitive antennas: the wavelength of the 2.4 GHz is much shorter than that of the conventional frequencies of 27 MHz and 72 MHz, it is very susceptible to loss of signal which results in a receiving error (according to 6EX-2.4GHz reference manual, page 8) which seems not a good idea and even if cell phones can have micro-strip antennas why they haven't adopted that technique?

Personally I am not much attracted by this big boom of spread spectrum for R/C since it doesn't seems to give a BIG advantage... and could be a marketing strategy to gain money from big dumbs .
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Old Apr 10, 2007, 06:04 AM
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Quote:
Originally Posted by Rox
Futaba has recently released 6EX-2.4GHz system with R606FS receiver which has two antennas ... with a requirement that the two antennas should be placed at 90 degrees to each other

First question: is that really necessary to shift to 2.4 GHz band rather than 72 MHz even most of the fields that I visit are not that much crowded!!!
"If running well, leave well alone"..

Quote:
Second: Having TWO sensitive antennas: the wavelength of the 2.4 GHz is much shorter than that of the conventional frequencies of 27 MHz and 72 MHz, it is very susceptible to loss of signal which results in a receiving error (according to 6EX-2.4GHz reference manual, page 8) which seems not a good idea and even if cell phones can have micro-strip antennas why they haven't adopted that technique?
Multipath and water absorption are both two ways the 2.4Ghz signal can go bad on you..thats why two aerials at right angles work..if one is nulled chances are the other one won't be..

Quote:
Personally I am not much attracted by this big boom of spread spectrum for R/C since it doesn't seems to give a BIG advantage... and could be a marketing strategy to gain money from big dumbs .
I think it is very good for park flyers flown by relatively unknowledgeable people and also for club scenarios. A LOT of shoot downs occur when people are just 'switching on to check the model'.

Plus the data rate is higher which should lead to better and more precise control. I think its a great step forward, but no reason to junk gear that is still working more than well enough.
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Old Apr 10, 2007, 06:52 AM
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Sao Paulo, Brasil
Joined Aug 2004
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2.4Mhz transceivers like Futaba's use Spread Spectrum, originally designed for military use. Since it changes the frequency quickly while operating any interference on a single frequency or even more will not cause trouble.

There is no need to make a frequency control, so I think it is the future.

I am not a big specialist on radios but I think their only mistake was using 2.4Ghz instead of 900Mhz. My friend works with industrial remote controls that can't fail and is currently using 433Mhz and 900Mhz frequencies because since most applications moved to 2.4Ghz, these lower frequencies are almost free.

Due to wireless networks, wireless phones and other things 2.4Ghz is much more clouded then 900Mhz, maximum allowed output power on 900Mhz is greater on many countries and 900Mhz waves have better propagation on long range and less possibility of blindness then 2.4Ghz.

I don't know if these 2.4Ghz hobby radios have something like that, but since both transmitter (on hand) and receiver (on airplane) are tranceivers, there is easy to give a lot of real-time information to the pilot, such as battery voltage, current, temperature, motor RPM, level of communication errors, alarm to get closer when communication errors are over a safe limit, and so on.

The bigger trouble is probably there will never a "standard" for these model DSS devices, as there is not a standard for PCM, so it will be harder to get a new receiver...
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Old Apr 10, 2007, 07:35 AM
Rox
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The data rate is higher, thats a plus if talking about a resolution of 2048 bit... but do we really need that much resolution with mechanical servos and linkages I don't buy that... there is a saturation point of mechanical efficiency versus bit-resolution of the R/C system!

So what I assume that 2.4 GHz ISM band systems are good for so many cheap chinese made park flyers with limited output power ... aiming at "relatively unknowledgeable people" and BTW 2.4 GHz is least preferred band for RF!

I may be wrong but this is not the right track for future R/C electronics according to the experience I have gained.
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Old Apr 10, 2007, 09:07 AM
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There are also currently many FCC part 15 certified 900Mhz modules, and those modules are cheap if you want to build your own system. One of them is about $60 for the TX/RX pair and runs at maximum allowed power. As far as I know, you could use frequency hopping, and automatic channel selection with a 900Mhz system, so it could have most of the benefits. The one big thing in favor of 2.4Ghz is the bandwidth, you can now easily integrate telemetry data back to the operator. Also because of the proliferation of 2.4Ghz devices, the RF modules are cheap!
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