2.4 GHz systems

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8 August 2010 at 20:24 #5091
Tony Burton
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@tonyburton83970
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8 August 2010 at 20:24 #28012
Tony Burton
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@tonyburton83970
I have an interesting question.

Recently a pal in our model boat association told me that the maximum amount of 2.4GHz sets in use at the same time ( in model boats) should be no more than 30.

I was under the impression that any amount could be used. Not that we have 30 in our gang yet
8 August 2010 at 21:01 #28013
ashley needham
Participant
@ashleyneedham69188
SHOULD be , or COULD be ??

This sounds like a tech-y question centering how many channels are available in the regulated frequency band, and more specifically how many channels the sets are programmed to be able to see. A manufacturers answer I think…OR if no answer is forthcoming, 50 volunteer modelers with 2.4G sets attempt to sail simultaneously on the same small pond….and see what happens…

I can feel a need to sit down with a small whisky coming on, before digesting the inevitably tricky forthcoming answer…

Ashley
9 August 2010 at 07:30 #28017
Tony Burton
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@tonyburton83970
Thanks Ashley.

I guessed that would be a bit of a poser

I like the idea of a whiskey……………make mine a large one

Tony

P S……..what are the strange fonts that keep appearing in the forum letters
9 August 2010 at 13:21 #28018
The Long Build
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@thelongbuild
I thought it was more like 80. ?
9 August 2010 at 20:45 #28032
M. Graff
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@m-graff
There shouldn´t be any problems with over 80 users either as long as they use FASST systems.

The channel jumping happens so many time per second that it is no bigger control-lag even when so many users are at it at the same time (compare to model airplanes where lag could be troublesome), and don´t forget that the reciever compares the new pulse train with the previous one to avoid mistaken signals.
17 December 2010 at 17:17 #29220
Dave Melville
Participant
@davemelville64810
Hi Tony

Just joined so thought I would try and give you my understanding.

Yes 80 spot frequencies split into two bands of 40.

More expensive sets use each spot in turn ( for mere milliseconds, I think) and start again at the beginning after channel 80.

Others select a clear spot from band 1 (spots 1-40) and another clear spot from band 2 (spots 41-80). I believe they transmit alternatively to each selected spot Receivers for both these sets have two aerials.

Less expensive sets select a single clear spot from within the allocated spots, receivers have one aerial.

All sets have a unique id between the transmitter and receiver (the binding process) and receivers will ignore signals that do not contain the correct id.and as mentioned previously they have built in error correction routines.

There has been some debate as to the ability of transmitters to hop to another frequency should the chosen spot become unusable but apart from the first two mentioned above this seems unlikely once initial selection has been made.

So if 80 single clear spots are selected in theory there will be no spare spot for transmitter 81 and some interference might be expected.

In the case of FHSS, FSSS sets they are only using a part of the spectrum for milliseconds and whilst they may interfere with another user it would probably be transient and easily handled by the receiver.

I have both Futaba and Planet 2.4GHz systems and have had no problem with either. The Planet requires only 4 batteries (rechargeable) and they last for months (used every Sunday for 2months) without changing. The Futaba is somewhat more demanding and starts beeping after 2/3 hrs.

At my own club we have 15/20 regular sailors all on 2.4GHz and have no problems.

We do have a designated transmitter area to ensure that on switch on a spare spot can be correctly selected.

In practice I dread to think of 80+ boats on our lake. I have enough near misses with other member at present!!

I like the idea of a whiskey……………make mine a large one too!!

Dave
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