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Spektrum DX7

Old radio?

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Nigel R17/10/2019 14:21:42
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"Nigel: Its not quite as simple as you make out. Frequency hopping is NOT the same as spread spectrum. It is perfectly possible to make a frequency hopping system that is not spread spectrum."

Not, it is indeed not the same, although I was trying to keep my post as brief as possible. DSMX - with its (pseudo) random hops across all available channels within the 2.4GHz band (24 or 27 of them) - achieves the spread across the whole band (with its associate redundancy) as well as a low duty cycle on any given channel within that band.

"Frequency hopping adds an extra layer of resilience on top of spread spectrum, but much of the immunity comes simply from the spreading process, regardless of frequency hopping"

Yes, so admittedly you could do a spread method without hopping, but freq hopping is the easy route when the existing technology in mobiles has been developed already, plus the hopping with its low duty cycle allows for a lot of simultaneous devices to use the band without interfering, and the low duty cycle means you don't have to implement look before transmit.

Other methods are certainly available, but we are here, with the prevalent technology being hopping.

Peter Christy17/10/2019 14:27:09
1582 forum posts

And of course, the *best* option is spread spectrum plus frequency hopping with a high MUF (duty cycle, though its a bit more than that - for the pedants!). But for that, LBT is mandatory - in the EU, anyway!

--

Pete

Trevor Crook17/10/2019 22:40:29
864 forum posts
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C8, I believe the reason the DX7 charge connector is reverse polarity relative to common convention is that in those days, Spektrum used effectively a JR Tx case, and the two brands shared a lot of technology. For that tranny, Spektrum retained the JR convention. Don't know what JR were thinking though.....

Cuban818/10/2019 07:29:11
2758 forum posts
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Posted by Trevor Crook on 17/10/2019 22:40:29:

C8, I believe the reason the DX7 charge connector is reverse polarity relative to common convention is that in those days, Spektrum used effectively a JR Tx case, and the two brands shared a lot of technology. For that tranny, Spektrum retained the JR convention. Don't know what JR were thinking though.....

So it's all JR's fault.......laugh

A good presentation from dear old Bruce on Spread Spectrum form 2011. Bruce haters, please ignore wink

Edited By Cuban8 on 18/10/2019 07:31:15

Peter Christy18/10/2019 09:07:24
1582 forum posts

I don't think there ever was a "common convention" for the polarity of the chargers. Even aftermarket power supplies for electronic devices had reversible plugs to accommodate the different polarities.

This is why most manufacturers fitted protection diodes, to prevent reverse polarity connections doing any harm. Oh, and most modern peak detect chargers work very well with the diode still in place! It was only very early ones that got caught out by the diode. No need to short them out these days, unless you have a very old charger!

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Pete

Engine Doctor18/10/2019 10:57:21
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Posted by Trevor Crook on 17/10/2019 22:40:29:

C8, I believe the reason the DX7 charge connector is reverse polarity relative to common convention is that in those days, Spektrum used effectively a JR Tx case, and the two brands shared a lot of technology. For that tranny, Spektrum retained the JR convention. Don't know what JR were thinking though.....

C8 You are correct, infact the labels on my DX7 says Made by JR so would explain it. Easily overcome

Steve J18/10/2019 11:04:57
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The original DX7 was a JR 2720 with a Spektrum RF board.

Nigel R18/10/2019 11:08:43
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"A good presentation from dear old Bruce on Spread Spectrum form 2011"

Yes.

As far as I know, the Spektrum protocols DSM2 and DSMX both do this within the channel they are transmitting on.

DSMX then adds "slow" hopping between the various channels, on top of this.

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