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Old Oct 20, 2004, 09:39 AM
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pkrska's Avatar
Toronto, Ontario, Canada
Joined Jan 2004
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No More Crystals!! No More Interference??

Take a look at this product:
http://www.rcuniverse.com/product_gu...product_id=194

Could this be used for aircam? It has a fail safe built into it. Cool. But it does state it is for 3 channels only. I bet with a modification to it, it could be used for aerialphotography. Hmmm?

The article talks about how crystals glitch and have many interference problems. I was not aware of this!

I own a 2.4Ghz Blackwidowav product and that does have interference problems especially if the antenna is not properly orientated for the duration of the flight. My plane was being controlled by a crystal receiver and transmitter and it did not experience any problems during the flight, it was only the video that was cutting in and out. Perhaps I was not aware of all the glitches that was taking place and perhaps it is taking place and I do not see or hear it!?!?!?

If someone could explain the problems if any - when using crystals compared to using a 2.4Ghz frequency. So what is the dilio here? Are crystals more reliable or not?
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Old Oct 20, 2004, 12:44 PM
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Mr.RC-CAM's Avatar
USA
Joined Oct 2001
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Quote:
But it does state it is for 3 channels only.
The DSM's target market is for R/C ground vehicles.


Quote:
The article talks about how crystals glitch and have many interference problems. I was not aware of this!
Marketing hype at its best. Glitches are not because of xtals, per se. I suspect that the DSM system has an xtal buried in it (it is a cost effective way to ensure stable RF).

The DSM system's claim that crystals are not needed is because it has an endless availability of uniquely coded "channels" built into it. The system uses spread spectrum, like a wireless LAN would use. It is not using the traditional RF carrier we are used to. The spread spectrum signal includes error correction and a unique ID to match your Rx to your Tx. This allows your Rx to only respond to your Tx.

It too will be affected by interference. However, it will be able to accurately detect the interference and safely respond with a failsafe condition. So no "glitches." Slower servo movement, or total loss of servo movement, is what you get instead.


Quote:
I own a 2.4Ghz Blackwidowav product and that does have interference problems especially if the antenna is not properly orientated for the duration of the flight.
Microwave RF is like that. It is very directional, easily absorbed by vegetation, prone to serious multipathing interference, and such. Also, mW for mW, our 72Mhz frequencies are substantially more efficient {at getting the signal out} than microwaves.

Frankly, I think the product's initial release for the ground vehicle market is a smart one. In my opinion, unless they get the FCC to change the Part 15 rules to up the RF power for 2.4Ghz operation, or they use a diversity antenna system, the microwave R/C systems may not be the best thing for everyone.

Keep in mind I have not tried one -- I'm just extending my experience with microwave RF devices onto this new R/C product. So, we will see if I am dead wrong about these early DSM systems. Of course technology is not static, so eventually this sort of R/C stuff will satisfy our needs.

RC-CAM
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