Spektrum and Futaba id wonder

[CaptDen]

I was wondering if anyone can tell me how these 2 manufactures can be sure that neither can use the others unique id that is used on the transmit receiver binding. Since Futaba has seen a manufacture clich with id's. I was wondering if the 2 manufactures are keeping this straight so that we don't see an issue between manufactures.

[DavidH]

From my understanding they both use different protocols.
Spektrum locks on to two frequencies in the band
Futaba is constantly hopping between frequencies on the band.
XPS does similar to Futaba.
I doubt one receiver could interpet the other transmitter even if they had the same GUID.

David

[Pinecone]

They also use different frequencies in the band.

[DavidH]

They also use different frequencies in the band.

What frequencies is Spektrum/ JR using the in 2.4 ghz band?

There is 80 frequencies in the 2.4ghz band.
Futaba continously hops between the 80 frequencies in the 2.4 ghz band
XPS does the same except
Only changes frequencies when potential interference is encountered

Spektrum/JR locks on to two open frequencies of the 80 in the 2.4ghz band

David

[wlfk]

To be pedantic, there are an infinite number of frequencies in the band. The number of channels is an arbitrary decision made by each mfr.

I agree futaba and spektrum radios are unlikely to interfere with each other. Unfortunately Futaba radios now sometimes seem to share GUIDs.

K

[DavidH]

From all the charts I have seen. I have only counted 80 freguencies in the 2.4 ghz. So don't know so much about there being an infinite number.
Even Spektrum states on there website that if 40 of there trannys are on. That when the 41st turns on it, it probably won't bind till there is clear frequency.
Now as for the GUID's I would think there is infinite combinations of those numbers.
Yes Futaba had a few of 6EX's, 7C's and TM-7 get pass that had all 0's for GUID's. Those trannys will only affect another tranny that happens to have the all 0's for GUID's.
Only been a couple of incidents reported. One in the UK and one in Arizona.

David

[Pinecone]

There are lots of frequencies available on the 2.4 GHz band we use. It is a unlicensed band, so there are no set frequencies to be used for any given purpose. The downside is, someone esle can pick one of the frequencies we use for some other use.

The band runs from 2.4 - 2.5 GHz, or a 100 MHz band width. Consider, the ENTIRE spectrum from 0 - 72 mHz, with all its users, is less than 3/4 of the 2.4 bandwidth available. And figure, our current 72 MHz channels are 10 kHz wide. At that (althought the bandwidth usage is different) there are at least 1000 "channels" that wide in the 2.4 GHz band.

http://en.wikipedia.org/wiki/ISM_band

Spektrum picked 80 such frequencies to be used as their "channels" and each Tx uses 2 of them, but 1 is used for the link process, so 39 Txes can be working at one time.

Futaba picked 36 (from what I have read) frequencies to use at their "channels" and they hop between those 36.

There is no reason for the Futaba 36 to any way overlap the Spektrum 80.

[BarracudaHockey]

To add to what David said, the GUID is only part of the protocol, a Spectrum reciever wouldn't necessarily even see that portion of a signal as its GUID, nor is there any technical info out there to say they even use the same number of bits to generate GUIDs.

[Pinecone]

Actually there is a finite number of GUIDs depending on how many bits/digits they use.

And due to using spread spectrum, the "channels" can overlap between different types of systems without problems.

[kamtsa]

Spektrum picked 80 such frequencies to be used as their "channels" and each Tx uses 2 of them, but 1 is used for the link process, so 39 Txes can be working at one time.

So, this is not really 'spread spectrum', right?

I had the impression that this band requires spread spectrum in one form or another.

kam

[Pinecone]

It is spread spectrum. The use digital spreading technigues withint each channel. http://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum

Frequency hopping is another method.

And the two can be combined. Both have their advantages and disadvantages. But they all work.

[kamtsa]

It is spread spectrum. The use digital spreading technigues withint each channel. http://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum

Frequency hopping is another method.

And the two can be combined. Both have their advantages and disadvantages. But they all work.

I see, they do DSSS within each 'channel' and the channel frequencies do not overlap (they could).

As for switching channels when the link quality degrades, I am not sure if this by itself qualifies as 'spread spectrum' as theoretically it can stay for very long time on the same channel.

Anyway, it works great for me. Never had any radio problem with the DX7 even with gliders.

Kam

[Danal Estes]

Part of the problem is, we use old terminology to talk about new tech. People say things like "Spektrum picks two channels..." or "XPS picks a channel and changes if link quality..." or similar. In both cases the word "channel" is very misleading. They pick a center frequency and spread from there, via different techniques.

And, as mentioned, there are not 80 channels. As mentioned, this was an arbitrary decision by Spektrum. Want further proof? Look up the way 802.11 uses the 2.4G band. They have 14 channels (only 11 usable in USA) in that exact same band where Spektrum has 80. Arbitrary, and up to each protocol.

Want to be even further wierded out by the way spread stuff works? The 802.11 channels overlap. That, if nothing else, should convince you the the word "channel" for spread means NOTHING like it meant before. Overlapping 72Mhz or 35Mhz channels would be disastrous.

The spread/despread process causes "digital gain". It also "de-gains" anything that's not on your spreading code. So, back to the very original question: Can GUIDs collide across manufacturers? The answer is a resounding NO, because they will never even "hear" each other's data packets... they use different spreading techniques, and each separate process for spread/despread gain ensures they see each other as noise, not data.

It is very similar to how you can fly (any of the big 3 systems) near 802.11 APs (plural) that are, by being plural, using the "entire" 2.4G band, yet everything still just works. Spread/despread gain within each system, each with a different method and a different chipping code, ensures that they never "hear" each other.

Very weird, and very non-intuitive stuff. Works like a charm. :)