RunRyder - DX7 coexisting with other 2.4ghz systems

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Radio - JR & Spektrum DSM > DX7 coexisting with other 2.4ghz systems

G-Force Heli
Senior Heliman
Location: Ontario, Canada

Don't know if anyone have asked this question before.

Are other companies that coming out with 2.4ghz systems going to also scan for 2.4ghz frequencies that the DX7 is using before locking the Tx onto one?

01-30-2007 Over year old.

d_wheel
Senior Heliman
Location: Deep in the heart of Texas.

Apparently, Futaba does not. They are using frequency hopping without listening first....

http://at.robbe-online.net/rims_at..../View/1&2DF4068

Go to new items, radio control systems, bottom of page. Click on T-6 EXP 2.4 ghz.

Later;

D.W.

Gettin old aint for sissies!

01-30-2007 Over year old.

hrosee
Senior Heliman
Location: Richardson, Texas

I just read the Futaba solution. They must be using slightly different frequencies on 2.4 or we are going to have a big mess!

01-30-2007 Over year old.

HOMEPAGE

Barney
Key Veteran
Location: Inverness Scotland

I'm no expert but this is part of the specs below..it is also a park flyer set so presumably is not full range/output?

The Futaba system if I understand correctly is constantly channel hopping. (see below) Whereas a DX7 with AR7000 locks onto 2 seperate channels and so would not be susceptial to interference from this because it will disregard a corrupt signal from RX 1 and take informaton from the second Rx..

Futaba 2.4ghz

The transmitter and receiver of a FASST modulation system constantly jump from channel to channel at the same rhythm, at a rate of several times per second. Since the system only occupies a particular spot frequency for a very short period, narrow-band interference is suppressed very effectively. FASST technology eliminates the need for a scanner in the transmitter, as the transmitter and receiver are constantly and synchronously swapping frequencies in any case.
For unambiguous identification the transmitter also sends an individual code. Channel clashes are virtually inconceivable, as there are more than 130 million possible code combinations.

01-30-2007 Over year old.

G-Force Heli
Senior Heliman
Location: Ontario, Canada

I don't know how Futaba can get around this. I wouldn't want a transmitter to jump on to my channel in use regardless how short a period.

There would be a need for all manufacturers to agree on this or else I can see the frequency board coming back.

Correct me if I am wrong.

01-30-2007 Over year old.

Barney
Key Veteran
Location: Inverness Scotland

You are right in what you are saying in theory...but if that were the case then only one Futaba Tx would occupy the whole 80 available channels (although constantly hopping). Cant see them digging a hole for themselves that deep to prevent even them from using more than one Tx at a time.

If there is someone better qualified in the house please step forward..

I would suspect the checksum encoding that is individual to every Tx/Rx by binding will filter out the hicups..I did notice in the picture from the link the Fut Rx has two aerials attached..so maybe it's got a 2nd Rx component similiar to the Spektrum AR7000 system?

01-31-2007 Over year old.

MikeC
Key Veteran
Location: Wausau, WI

Anything that operates on the 2.4Ghz band, by FCC rules, has to use collision avoidance, in other words it can't transmit on a channel that is already in use. If it doesn't do this it can't be on this band.

Mike

Century Swift, Hirobo Sky Robo, Spektrum DX7

01-31-2007 Over year old.

TMoore
rrProfessor
Location: Cookeville, TN

Let's ask Paul Beard to comment as he probably knows the ins and outs of the 2.4 Ghz band better than anyone.

I do know that frequency hopping and spread spectrum don't work the same way so if say a Spektrum radio can co-exist with let's say a 2.4Ghz router why not a freq hopper?

BTW, Tower is showing the Car radio FASST technology now.

TM

"If you can do it, it ain’t bragging." - Will Rogers

01-31-2007 Over year old.

JKos
Elite Veteran
Location: Town of California in the state of Maryland

> Anything that operates on the 2.4Ghz band, by FCC rules, has to use
> collision avoidance, in other words it can't transmit on a channel
> that is already in use. If it doesn't do this it can't be on this
> band.

This is not at all true and a common myth of the 2.4 GHz ISM band.

In order for a frequency hopping system such as the new Futaba, XPS, or Nomadio to interfere with a "fixed" frequency system such as the Spektrum, a lot of factors must come into play. First, both systems have to occupy the same channel at the same time. Since both systems only transmit for a very short time each time they transmit the probability of this is low to begin with.

Then, even if this happens, you still have spread spectrum on your side because the two signals will look like noise to the opposite receiver. This is the biggest beauty of spread spectrum. The desired signal is "amplified" by the despreading process while other signals are "attenuated" at the same time.

So, now that spread spectrum has come to the rescue in terms of signal-to-noise ratio, the offending signal would still have to be strong enough to cause enough chip errors to cause enough bit errors to cause the error correction coding to not be able to correct the corrupted bits.

And this has to happen on both Spektrum channels at exactly the same time for a dropped frame to occur.

> I do know that frequency hopping and spread spectrum don't work the
> same

You are correct, pure frequency hopping and pure spread spectrum are completely different. However, the frequency hopping systems we are talking about here are called hybrid systems which do both at the same time.

- John

Protos -- Logo 14 -- Logo 10

01-31-2007 Over year old.

hrosee
Senior Heliman
Location: Richardson, Texas

If you read the description carefully and look at the specs it jumps from 36 differnt frequencies called "spot frequencies".

We know the Spektrum system uses 80 channels total.

I would suspect that the systems are using different frequencies.

01-31-2007 Over year old.

HOMEPAGE

JR-Spektrum
Heliman
Location: Champaign, IL

Quote
Let's ask Paul Beard to comment as he probably knows the ins and outs of the 2.4 Ghz band better than anyone.

I couldn't explain it better than this:

http://www.rcgroups.com/forums/show...&postcount=3974

Paul

01-31-2007 Over year old.

HOMEPAGE

MikeC
Key Veteran
Location: Wausau, WI

This is off of Spektrums site:

Quote

What happens if two transmitters are on the same frequency?
To be FCC legal, all 2.4Ghz devices must incorporate a collision avoidance system that prevents the system from transmitting on an already occupied frequency. The chance of two transmitters occupying the same frequency is highly unlikely. If two transmitters should somehow end up on the same frequency, other safeguards, such as the GUID and proprietary time base coding, will prevent interference. Of course, with the aircraft system, the transmitter is transmitting on two frequencies simultaneously. The odds of two transmitters transmitting on the same two frequencies is even, more unlikely but again, should this happen, other safe

Century Swift, Hirobo Sky Robo, Spektrum DX7

01-31-2007 Over year old.

raptor50luvver
Veteran
Location: southampton UK

Futaba will not get Uk approval if it is possible to interfere with the already allowed Spektrum system,,,ha ha

01-31-2007 Over year old.

Seaknight1962
Senior Heliman
Location: Bremerton, Washington 98312

I guess that until all the bugs are worked out from either system, I will keep using my frequency pin and the dreaded frequency board.

Seaknight
Semper Fi

01-31-2007 Over year old.

HOMEPAGE

clive45
Veteran
Location: NSW Australia

I have always understood that if 2 tx's get on the same channel it does not really matter as the RX will only listen to the signal with its unique code and all other signals are treated as background noise. The spectrum picks 2 empty channels for best comms, but if another signal turns up on its channel it ignores it.
That's just my understanding of the situation. I cannot see Futaba or any other manufacturer tooling up to produce something that's not going to get approval. The thing that worries me is the approval system up to the task of checking for potential problems with the different systems that will be available in the not to distant future.
Can you imagine the problems and fights at a flying fields if this problem arises.

01-31-2007 Over year old.

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Radio - JR & Spektrum DSM > DX7 coexisting with other 2.4ghz systems

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