2.4GHz Band Saturation

It seems possibly the most misunderstood aspect of 2.4GHz radios is how many can be used at one time and if that saturation point is met, what happens?

1. The number of radios that can be used at 1 time is LIMITED. This exact number of radios that can be used at 1 time varies according to several factors, but indeed it needs to be know that the band can only handle a limited number of radios in-use at 1 time. (more on that a little further down…)

2. IF that saturation point is reached, generally “more” radios will not be able to be “turned on”. They will search for an open frequency, will not be able to find one, and will simply wait until one is available. In “some” conditions, the FHSS systems might turn on, but will be slow (It’s OBVIOUS)…

 Some companies have talked more about this than others, but here’s the scoop…

The high-output portion of the band we use in 2.4GHz (as regulated by the FCC) is split up, somewhat arbitrarily by our systems (each company has their own way of dividing up the frequency band).

 FHSS radios bounce around the band, Spektrum and other DSSS or DSM systems simply chop it up into about 80 frequencies (in the aircraft side of things, they use 2 of those frequencies…)

So, indeed only about 39 DSM/DSSS aircraft systems can be in use at 1 time if Spektrum is the only radio in use. (see a link to Spektrum and a quote from their website at the bottom).

 If you mix all the different brands and their proprietary type of signal/system, generally, the total number of radios that can be on and function 100% reliable without slow down, etc. is about 36 for aircraft (surface gets more because when only surface systems are in use, Spektrum is only using 1 frequency at a time instead of 2).

Now, that 36 number can vary, but in our practical testing, we’ve found it’s right around 36-39.

At that point, the DSSS and DSM systems will no longer find a clear signal and the other brands start to slow down a little.

 What it means: EXCERSIZE frequency control at major events or busy flying fields!

Is 2.4GHz better? SURE, OF COURSE!!!. If too many radios turn on, either they will not find a frequency and will not transmit or they will work but just with a little delay (thus you’ll see it and probably just turn off anyway) unlike 72MHz where if some one just “turns on” without concern, he can knock you out of the sky!

So, 2.4GHz is GREAT but there are still limitations and you and your club/flying field might want to consider those limitations.

I hope this helps.

Mike

Note these quotes from Spektrum brand:

http://www.spektrumrc.com/DSM/FAQ.aspx 

Quote from Spektrum:

What happens if the band is full (80 users for surface or 40 users for aircraft) and I turn on my transmitter?

In the unlikely event that all channels are occupied, the next transmitter will scan the band indefinitely until open channels are available. The transmitter will then acquire the channel(s) and begin transmitting. Only then will the system connect.

Spektrum, DSM, Horizon, are all products copyrighted by Horizon Hobby.

www.horizonhobby.com

 I’m only mentioning them here to help create wider understanding of the hobby.

DSSS, Airtronics, Sanwa, are all copyrighted by Sanwa Japana and used by Global Hobby with permission.

(I’m not trying to step on anyone’s toes here!)

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