Spektrum DSMX

Discussion on the reviews of 2.4GHz radios, modules and receivers that have appeared on RCModelReviews..com

Re: Spektrum DSMX

Postby Juanlargo » Mon Sep 05, 2011 4:48 pm

I bought into the Spektrum hype twice. I got the DX6 when it first came out and then a DX7, not the DX7s. So far it has been OK with one problem that required a trip to Horizon but other than that pretty solid.

As for Bruces question on a chip rate to cover the entire 2.4 GHZ window I'm not shure what the bandwidth is. I do know that direct sequence spread spectrum is much better than frequency hopping for RC applications but is expensive to implement and requires more precise timing. My next 2.4 GHZ radio will likely be a Futaba or a Hitec, I know they work.
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Re: Spektrum DSMX

Postby GBR2 » Thu Sep 08, 2011 12:09 am

I've always been hesitant about using any DSM2 system in anything other than the micro bind/fly models I bought as I just never really felt comfortable with the Spektrum system. However, I'd be more than happy to use the new DSMX system except for the fact that Horizon/Spektrum refuse to manufacture any DSMX modules for use in my XP9303 transmitter. Perhaps JR themselves might eventually do it but I'm not holding my breath. So I'll continue using my FrSky module, my DSM2 module with my bind/fly models, my 72 Mhz module and even my XPS module from time to time.
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Re: Spektrum DSMX

Postby Maxthrottle » Sun Sep 11, 2011 2:46 pm

Thanks Bruce. To bring out more of that grumpy old man ;) .... what are your thoughts comparing DMSS against DSMX. How are they dissimilar other than the protocols/timing not being compatible?
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Re: Spektrum DSMX

Postby RCModelReviews » Sun Sep 11, 2011 10:12 pm

I've contacted JR Japan to see if they'll be prepared to make a DMSS unit available for review but am waiting to hear back.

At least I got an acknowledgment that my email had been received -- which is more than I got last time I contacted them.

I strongly suspect that JR's DMSS system is also a hybrid DSSS/FHSS sytstem (hence the "Dual Modulation Spread Spectrum" name.

The big issue (for JR users) will be the variety and price of receivers that they have available for DMSS.

Funny isn't it, how back in the FM/PCM days, most manufacturers only offered one or two receivers for their products but Spektrum manages to convince us we need at least half a dozen (or more) different shapes and sizes of receiver.
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Re: Spektrum DSMX

Postby Sid Sideslip » Sun Sep 11, 2011 10:32 pm

RCModelReviews wrote:Funny isn't it, how back in the FM/PCM days, most manufacturers only offered one or two receivers for their products but Spektrum manages to convince us we need at least half a dozen (or more) different shapes and sizes of receiver.


I suspect their marketing department is bigger than their R&D one.
What goes up...better bloody stay up (until I say otherwise).
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Are they playing down the reasons to upgrade

Postby RyanNX211 » Thu Sep 15, 2011 2:54 am

The official word is that DSMX is only necessary if you fly in environments like Joe Nall or huge indoor events.

This week at Muncie, we had 4 crashes with AR500 receivers when total control was lost, AFTER QUALIFYING FOR THE ANNUAL NATIONAL CONTEST BY TYING FOR 1ST PLACE in each event.
Number of flyers at the AMA site
1st instance: one
2nd instance: 10
3rd instance: 12
4th instance: 1

Flights were made in DSM2 even though on the last crash I loaned out my upgraded DX8. (backwards compatibility) If Spek would acknowledge there were more reasons for the switch, I wouldn't be looking at other systems.
I have spoken with them on the phone and the transmitters and receivers are going back. In the first 3 crashes the voltages were btwn 5.0 and 5.07. Failsafe throttle cut never worked on the last and the battery was in many pieces when it hit the asphalt. We only salvaged the tail skid on that one.
In any event, in spite of qualifying for the biannual contest in Vegas, we won't be going because : We don't have any models left and not enough time to build replacements! :cry:

But the father son team who got all our 72Mhz equip two years ago will be...
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Re: Spektrum DSMX

Postby RCModelReviews » Wed Sep 21, 2011 7:18 am

Good news... JR Japan have agreed to make a JR XG8 DMSS system available for review.

It will be very interesting to compare this system to DSMX.

This will get a priority review as soon as it arrives.

If only Futaba and Spektrum were as confident in their products as JR and Hitec.
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Re: Spektrum DSMX

Postby RyanNX211 » Wed Sep 21, 2011 12:42 pm

Is there any chance you could study the range of these systems? I've heard rumors that
the DX8 has less range than the old DX7 which was pretty good.
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Re: Spektrum DSMX

Postby Juanlargo » Mon Oct 24, 2011 6:25 pm

Actually the range should not be impacted. Direct sequence spread spectrum spreads the signal out using a sign of X over X modulation scheme. This makes it far less susceptable to interference or jamming. In the demodulator the P/N, or sread sequence is recovered from the stored binding data. This sequence is vector summed with the signal. When the P/N sequence aligns the signal vector sums to one (it de-spreads), and if they do not sync then the interfering signal vector sums to zero and is spread down into the noise leaving only signal. Because of this ability to so successfully reject noise the DSMX system should have better range than the older static system.
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Re: Spektrum DSMX

Postby oldsapper » Mon Nov 14, 2011 10:57 am

Jeez, I wish I knew what Juanlargo was talking about....personally, I just get 'em off the deck (mostly), and hope to bring them down with as little damage as possible !! DSM2 is still OK in the Barossa Valley.
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