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Old 06-08-2012, 06:23 PM
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rcers
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Originally Posted by fmw View Post
The chances of two transmitters choosing the same two was remote, hence, no interference.
Actually the chances were not remote - especially as you had more systems on. They used 2 of 40 channels so with just a few transmitters on they indeed might be on exactly the same channel. But that was not really an issue.

Proof is in the testing. On DSM and DSM2 (fixed channel selection) you could have many (100+) systems on before the noise floor really started to cause any issues and even then they were minor issues. Pretty slick eh?

Originally Posted by fmw View Post
If two did choose the same two it would cause interference.
This is absolutely wrong. The system also had a GUID it sent. So your TX and RX "know each other". The receiver only listens to the TX it is "bound" too. That is what binding does - links the two together. The joy of spread spectrum systems is you can have two or three or more on the same channel but they don't listen to all the signal - just the one meant for them.

This is why Spektrum could happily exist with "other" frequency hopping systems that would transmit right on YOUR channel. Again no biggie - until you start getting signal saturation. Then things "slow down". But you still don't likely crash planes. But you might start seeing the plane get sluggish to controls (bad).

The signal saturation (noise) of all the systems in that 2.4GHz range is were we started to see issues at the HUGE events. Huge means 500+ pilots. There with the chance of 100-200-300 systems "ON" at the same time just saturate the entire band with signals. The systems all coped with that remarkably well - even DSM/DSM2 with fixed channels. Spektrum DMS2 was at 'more' risk so they introduced DSMX that hops. Most agree that is vastly better.

Hitec goes one step further than anyone. They not only hop - but can adapt. So as they see saturation on specific channels, it avoids hopping to those channels - excellent!

Originally Posted by fmw View Post
Also, this random frequency selection would mean that it is also rare for the transmitter to choose one of the two frequencies to match the local cell tower or whatever.
Cell systems don't use 2.4GHz - so no issue with cell phones.

Originally Posted by fmw View Post
But when it does, it creates interference.
Again - NOPE.

Those spread spectrum engineers are pretty sharp folks!

Mike
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