DSM-J, JR's Frequency Hopping 2.4GHz RC System

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My Credentials
So who's doing this reviewing then?

Well I've been building and flying or driving radio controlled models for over 40 years and during that time I like to think I've built up a reasonable amount of knowledge.

I'm also a qualified electronics engineer who has worked in radio frequency, analog, digital systems and software for more than three decades. In fact I designed and built my first RC set back in 1969.

For the past nine years I've also been involved in the design and manufacture of some rather sophisticated engine technology and UAV flight control systems.

So, chances are I've been there, done that and have a huge pile of tee shirts to prove it.

Right now I'm heavily into 3D flying and enjoy all aspects of the RC hobby. I may be old but I don't feel it.

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Cheap Chinese Engines: Just how good are those cheap Chinese glow and gas engines that sell for half the price of their "brand-name" equivalent? I put several to the test.

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NEWS: JR Now Pushing Its Frequency Hopping System

WHY FREQUENCY HOPPING?

Dated: 16 Apr 2010

JR users in Australia, New Zealand and the UK have noticed recently that the company is pushing its DSM-J system in preference to the previous commitment to DSM2.

What's behind this move and just what is the difference between DSM-2 and DSM-J?

A little history

For many years now, JR has been pushing DSM2 as its 2.4GHz standard, both in the USA and most other marketplaces.

It became clear that JR found the Spektrum-designed DSM2 system to be the shortest route into the spread-spectrum market and one presumes that some kind of deal was done that gave Spektrum access to one of JR's transmitter designs (on which the original DX6 was based) in return for making the RF side of things available to JR.

The only problem was that DSM2 is a DSSS system which uses just two portions of the band and doesn't hop once a link is established between transmitter and receiver.

In some countries, non-hopping systems are restricted to much lower power levels than those that do hop so this left JR with a problem. Even in its homeland of Japan, the DSM2 system was actually illegal, since it had a power output well in excess of the 10mW allowed for non-hopping systems.

To cater for this special market, JR devised the DSM-J system -- a system that reportedly provides full-time frequency hopping so as to meet the more stringent Japanese rules for the 2.4GHz band.

Although DSM-J was widely sold in Japan, the rest of the world were not offered this more frequency-agile option and thus DSM2 was the only choice on the menu for the rest of us.

JR now pushing DSM-J

But now things seem to have changed and JR is strongly promoting its frequency-hopping DSM-J system in a growing range of countries outside of Japan; countries that were previously only offered DSM2.

So what's behind this change of heart on the part of JR?

To be honest, I have nothing but speculation to offer but here's what I think may be happening...

JR would like to break away from DSM2 as its 2.4GHz offering for several reasons.

Firstly, it would allow them to provide a more resilient 2.4GHz connection than DSM2 is able to offer. As seen in this test, DSM2 is occasionally vulnerable to strong interference that would leave a frequency-hopping system unaffected.

Secondly, I suspect that JR doesn't like the fact that purchasers of its DSM2-based 2.4GHz radios can source cheaper receivers under the Spektrum label, effectively ignoring the pricier JR-branded offerings. Since DSM-J is completely incompatible with DSM2, the switch would be another move (just like Futaba's S-Bus) by a major manufacturer to "lock-in" customers to their own branded products.

What about U.S.A. JR-users?

Again I only have suspicions but I think that US customers will be denied the benefits of DSM-J for a while longer, mainly because the US Spektrum distributor (Horizon Hobby Inc) are also the JR distributors.

As distributors of both, Horizon would probably prefer to see its JR customers given as wide a choice of receivers as possible, and that means sticking with DSM2.

Testing DSM-J

Now I'd love to say that I have a review of the DSM-J system all lined up and ready to do but, unfortunately, I don't.

For some reason, the big-name RC brands (except Hitec) seem totally unwilling to provide equipment for truly independent review purposes. Sure, they'll send samples off to RCU and RCG where they can rely on nothing but effusive praise -- but when it comes to RCModelReviews.com where the truth is worth more than any amount of advertising dollars, they're just not interested.

You'll have to figure out why that is for yourselves but perhaps the DSM2 flaw I highlighted recently and every other "paid" reviewer seems to have ignored might provide some clue.

If I can, I'll try to convince someone using a DSM-J system to lend it to me for review purposes -- or maybe JR will step up to the plate and show that they have real faith in this system by organising a review sample, who knows?

RCModelReviews.com readers are invited to lobby JR and suggest they submit a DSM-J system for honest and objective review here.

In the meantime, we'll just have to wait and see.