RCModelReviews and Spektrum/Horizon

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Re: RCModelReviews and Spektrum/Horizon

Postby aesmith » Mon Sep 13, 2010 11:22 am

RCModelReviews wrote:That I was able to completely disrupt the DSM2 link using something as simple as a video-sender and that this was replicated by a colleague using just a 50mW video sender is somewhat worrying. These video senders are sold in large numbers and some people are using them on RC models for FPV purposes which means the scenario where a DSM2 system selects 2 closely-spaced channels and then someone turns on a video sender that also occupies the same part of the band is a small but definite possibility.


How do these video senders choose what frequency to use?
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Re: RCModelReviews and Spektrum/Horizon

Postby cuban8 » Mon Sep 13, 2010 5:41 pm

RCModelReviews wrote:
cuban8 wrote:Sorry, but I just don't understand the hysteria surrounding the "Spektrum Problem". Yes I fully understand and accept the findings regarding the system possibly selecting channels that are relatively close, but just because it's been decreed that this might prove fatal if other random outside influences occur at the same time, doesn't mean the system's no good.

You are absolutely correct.

As I've said in my articles on the matter The sky is not falling.

However, it's not an insignificant issue either.

That I was able to completely disrupt the DSM2 link using something as simple as a video-sender and that this was replicated by a colleague using just a 50mW video sender is somewhat worrying. These video senders are sold in large numbers and some people are using them on RC models for FPV purposes which means the scenario where a DSM2 system selects 2 closely-spaced channels and then someone turns on a video sender that also occupies the same part of the band is a small but definite possibility.

What is of concern to me (and clearly other people) is not that this vulnerability exists in the DSM2 system, but that Horizon/Spektrum won't acknowledge it and fix it. All it would take is a tiny change to the code in the DSM2 transmitter -- something that could be done and tested in a day.

The only reason I can think of is that they don't want huge numbers of existing DSM2 users returning their equipment for an update to the new code -- so they'd rather not acknowledge the problem. Perhaps the new stuff is already fixed but they're not going to say anything for fear of that wave of "please update my old gear" requests, and the costs that would involve.

Yes, Spektrum's S/W designers have potentially left their product open to possible failure if a very unlikely set of circumstances occur. Too many ifs, buts, maybes, and random effects to really cause owners to lose confidence in their equipment IMHO.

The thing is that if Spektrum was a cheap Chinese system that cost just a few bucks I'd agree. However, Spektrum is pitched as a "premium" product and a leader in the field of 2.4GHz RC, with a matching price.

Why should people have to pay top-dollar for a bottom-shelf product?

It is the goal of RCModelReviews to help people make *informed* decisions when purchasing new stuff. They need to know that DSM2 is past its best-by date (for a number of reasons) and that it makes no sense to buy an RF system which is outdated and suffers performance penalties when, for the same or even less money, they can buy much more advanced and resilient systems.

One only has to look at a DSM2 installation in a large model to see how far behind the 8-ball Spektrum is now. Spektrum/JR advise you should use at least 3 satellite receivers and a data-logger to ensure reliable operation in such models and to keep an eye out for potential issues. By comparison, there are a huge number of FASST and other FHSS installations that work perfectly -- with just a single receiver and two antennas. Technology has advanced significantly since Spektrum designed their system but they are steadfastly sticking with old designs and (it would appear) buggy software.

What became very apparent in my tests is that there are now only two brands of 2.4GHz RC systems that select and stick with only two DSSS frequencies. These are DSM2 and the Chinese Assan (one of the first Chinese 2.4 products).

Every other manufacturer has now either gone to constantly-agile (FHSS) technology or opted to use at least three frequencies for redundancy. JR's launch of DMSS is another clear indicator that they don't wish to have their brand associated with the now aging and (in some cases) inadequate DSM2 technology.

How many wide band 2.4 gig transmissions (video transmitters?) would it take to swamp the whole band and render a FH system useless as well?

Well a video sender tends to consume about 1/4-1/5 of the entire band so in theory, as few as 4 video senders operating on different parts of the band would cover it. However, there are peaks and troughs in the video-sender's signal so even then, *some* of the FHSS system's signal would get through. In my testing, it's enough to provide a measure of control that would allow you to get your plane down in one piece. FHSS systems tend to degrade more gradually as you fill up the band with noise. DSSS systems just stop dead.

I don't know whether it's 4 or 6 or 8 or however many. Presumeably it could happen, so why don't we start worrying about that?

It'd only take 4-5 to cover the band -- but a good FHSS signal will still get through adequately to provide a modicum of control. And what's more, the chances of this happening are clearly a lot less than the chances of a single video transmitter being turned on while someone's flying their DSM2 system.

In summary: DSM2 still works for most people but it is now very much a "second tier" system -- so, why would anyone buy a second-tier system for a top-tier price when there are a raft of better options available that provide more insurance against being shot down by interference or suffering a receiver brownout?

The sky isn't falling -- but it's getting awfully cloudy in the Spektrum camp.



Thanks very much for that Bruce. Very nice explanation and I agree with your sentiments 100%. Certainly has given me food for thought as to why Horizon are ignoring your findings, especially if it's only a software update to fix things. I'm really interested in your findings with the DX8 as to whether the frequency selection issue has been addressed.
I'm still puzzled as to why Futaba only use a single RX whereas Spektrum go for all the satellites? I range tested an AR500 with my DX7 and orientated both aerials so as to get minimum performance (TX & RX aerials pointing at each other) I found that I was still getting full control at 40 paces, good sensitivity so no problem when the RX has a clear view of the TX.
Just one other thing - Spektrum say that their data logger enables you to optimise RX positioning within a model when there could be issues with the signal being shielded .Seems sensible to me to be able to check for signal fades caused by having an RX shielded by a motor etc. Why do Futaba not offer a similar tool? Surely the physics are the same whether FASST or DSM2?
Have Futaba invented a 2.4 signal that penetrates solid metal :lol: ?
How does a single 2.4 RX fitted to one side of a helicopter, for instance, cope when having it's view obscured by a large metal or carbon frame?

Cheers.

C8.
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Re: RCModelReviews and Spektrum/Horizon

Postby Tsurwolf » Mon Sep 13, 2010 11:21 pm

I have been a staunch supporter of JR for most of my hobby life ( FM/PPM ) but when the 2.4 systems started to be cheap i decided to go with an ASSAN module for my JR388S TX's.
I now have 4 TX's with 30 ASSAN RX's both V1 ( 6 off, 2 long antenna 9 channel & 4 short antenna 7 channel )and the V2 (7 channel long antenna) for the rest. In the last 2.5 years I have yet to suffer a radio failure.
During that time, I have seen a lot of crashes ( quite a few beginners in our club still on 36Mhz ) but the reason for this post, is that this weekend one of our younger and more experienced members lost a large scale ( read expensive) model to a lack of radio response. You just know what brand radio he was using right.
After the bits were recovered i gave some thought to the fact that this model was the THIRD ( of his ) and thought of the other crashes that have occurred ( one a twin Mitchel ) and which radio's were used by the pilot's.

Now i may be misguided and maybe in error in my assertions ( I am 64 after all ) BUT I know for a fact that at least 3 of the people who have suffered this lack of radio response ( and they are big expensive models ) have been using the "spectrum/JR spectrum" radios.

I just love my ASSAN X8 and will stick with it.

Cheers TBBW (aka: the big bad wolf)

btw: our field is in an open area away from houses and has 360 degrees of unobstructed grass runway's, with one transmission tower about half a K away, and two rec reserves behind the club house.
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Re: RCModelReviews and Spektrum/Horizon

Postby RCModelReviews » Tue Sep 14, 2010 1:44 am

aesmith wrote:How do these video senders choose what frequency to use?

Most of them have user-settable "channels" which allow you to change the portion of the band they use.
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Re: RCModelReviews and Spektrum/Horizon

Postby flying-things » Wed Sep 15, 2010 10:34 pm

I guess spektrum isn't going to reply. Shame on them.
I'd rather buy the chinese rx's and save money if they are going to ignore obvious problems.
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Re: RCModelReviews and Spektrum/Horizon

Postby gruvin » Thu Sep 30, 2010 9:21 am

Well gee ... anyway you look at it, not communicating with forthright confidence in their product is going to hurt them IMO — regardless of the facts.

I've been using Spektrum equipment exclusively since the original DX6 (park flyer DSM1 model). I've had absolutely no technical problems with any of it. However, with a certain amount of technical RF knowledge under my belt and as I've watched competing products emerge, boasting simply better RF schemes, I cannot help but face the facts. Fact 1, the technology is at least theoretically less immune to interference. Fact 2, the company acts in very suspicious and in some cases a downright unethical manner in this regard. (Just look at the fallout between Spektrum and JR over the apparent sneaky contract clauses. JR wouldn't be ditching DSM in hopes their customers will follow them into a whole new and non compatible system without good reason!)

Whilst I still enjoy flawless DX6/DX7 operation to this day, the company's attitude toward product support as well as feature restrictions is becoming intolerable. In the end, it was not the RF technology that had me lose faith in the brand, but the company's poor attitude. Good luck to them. I'm moving on.
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Re: RCModelReviews and Spektrum/Horizon

Postby TX_Winds » Mon Feb 14, 2011 8:33 pm

I know this thread has been dead for a while. I am just wondering if Spektrum/Horizon has given any response yet. I know they have just released DSMX. Perhaps this is their way of offering a fix for the problem and charging the customer for it.
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Re: RCModelReviews and Spektrum/Horizon

Postby RCModelReviews » Mon Feb 14, 2011 9:33 pm

No response.

I do feel kind of vindicated by the release of DSMX as I have been saying for some time that DSM2 is "past its best-by" date and indeed, the admission by Horizon (after a long period of denial) that they're having problems with DSM2 at large meetings does confirm what I've been saying.

It's also worth noting that they've been aware of the deficiencies of DSM2 in hi-noise environments for quite some time -- as their own pilots have been using/testing DSMX for quite some time.

However, I hope that now the air has been cleared (so to speak) they may decide to engage in some open and honest discussion regarding their 2.4GHz products. It's clear that the reason they wouldn't talk with me before was because they did indeed have something to hide.

Unless they still have something to hide, I expect they will be receptive (perhaps even pro-active) in establishing communications with RCModelReviews.
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Re: RCModelReviews and Spektrum/Horizon

Postby Buzzkill » Mon Feb 14, 2011 10:03 pm

I wouldn't hold your breath. Spektrum/Horizon are of the old school American business model that doesn't allow them to release or engage in any kind of dialouge unless they control the content 100%.

The only thing that rivals their tatics here in the USA is political races and televangelists.
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Re: RCModelReviews and Spektrum/Horizon

Postby RCModelReviews » Mon Feb 14, 2011 10:04 pm

I see Horizon have posted another DSMX promo video to YouTube.

Anyone wanting an independent review of the DSMX system by RCModelReviews could ask in the comments of that video whether they'll be prepared to have it put up for objective analysis and review.
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