New FHSS from JR?

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Re: New FHSS from JR?

Postby hhobbit » Wed Oct 27, 2010 2:33 pm

Hi Bruce
love the concept behind your site, and thanks for the heads up on possibilities of censorship elsewhere as regards unwelcome facts. I have used DX7 since the outset and apart from one crashin 2007 with a AR6100 in a Lepton havent had any issues; not even sure what was behind the crash but it was blinkin expensive!

What I had gathered from your well argued point was to beware of two adjacent channels vulnerable to say a high power video signal blocking them both simultaneously. If what you say about increasing activity in the band makes the DSM2 increasingly iffy, are there other sources to be wary of, or is there more stuff come to light? I find it hard to visualise problems from increased activity from model or nonmodel sources in the light of relatively few incidents at IRCHA, given the large number of Txs present, where else would have similar or worse concerns?
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Re: New FHSS from JR?

Postby RCModelReviews » Wed Oct 27, 2010 9:11 pm

The problem with the 2.4GHz band is that it's being used for so many things now it's hard to give a definitive list of possible interference sources.

The ones that may be most likely to catch you out are point-to-point data-links. These are set up to transmit data between two points and often involve the use of high-gain antennas at each end of the link. Because of the high-gain antennas, they broadcast a fairly narrow beam of energy on the 2.4GHz band that isn't visible until your model flies into it -- at which point you get a sudden loss of control.

Those people who have "dead spots" at their flying fields or their own little "Bermuda triangles" where lockouts are frequent on 2.4GHz maybe experiencing one of these signals crossing the field in that area.

Non-agile DSSS systems (like the Spektrum) are particularly vulnerable to these sources of interference because when the system links up, it's totally unaware that there's a potentially very strong interference signal perhaps just a few hundred yards away.

The best way to think of these beams is like a searchlight operating in daylight. Unless you're actually in the searchlight's beam, you wouldn't even know it was on but -- when your model flies into one it's dazzled and falls out of the sky.

It can be difficult to find the source of these data-links because they can be miles away (hence the reason they use high-gain antennas) and perhaps even beyond visible distance at ground level.

As I said -- the potential sources are manifold and this is just one.

We've lost DSM2-equipped models at our flying field (we have several WiFi repeaters and a number of suburban/school WiFi networks hidden by some trees) but not a single FHSS system has experienced any issues.

DSM2 will continue to work just fine for many lucky people but given the choice, when buying new gear for instance, I can think of no reason at all why you'd take the extra risk of buying 5-year-old technology when there's much better stuff available (at a lower price) from other suppliers.
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Re: New FHSS from JR?

Postby disco stu » Wed Oct 27, 2010 11:38 pm

The more I read on this, the more it makes 36mhz more attractive!! And as more and more people move to 2.4ghz, there is less chance of anyone else being on your frequency and lots of 2nd hand recievers to snap up as well :D
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Re: New FHSS from JR?

Postby RCModelReviews » Thu Oct 28, 2010 6:45 am

The old FM/PCM "longwire" frequencies still work -- but you still run the risk of being shot down by a kid down the road flying/driving their "toy plane/car" without your knowledge.

I think 2.4GHz is a great step forward -- bringing us smaller, lighter, cheaper, more reliable equipment that (except for a few notable exceptions) is almost totally bullet-proof in terms of interference rejection.

If you've still got longwire gear there's nothing wrong with using it -- but if someone's starting from scratch or buying a new radio -- 2.4GHz is the way to go -- just make sure it's a FHSS system.
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Re: New FHSS from JR?

Postby disco stu » Fri Oct 29, 2010 12:02 am

Fair enough. I thought you were pointing out cracks in the 2.4ghz thing as a whole that were only getting bigger. Will still get that hack module one day.......
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Re: New FHSS from JR?

Postby Engineer » Wed Nov 03, 2010 3:22 am

RCModelReviews wrote:The problem with the 2.4GHz band is that it's being used for so many things now it's hard to give a definitive list of possible interference sources.

The ones that may be most likely to catch you out are point-to-point data-links. These are set up to transmit data between two points and often involve the use of high-gain antennas at each end of the link. Because of the high-gain antennas, they broadcast a fairly narrow beam of energy on the 2.4GHz band that isn't visible until your model flies into it -- at which point you get a sudden loss of control.

Those people who have "dead spots" at their flying fields or their own little "Bermuda triangles" where lockouts are frequent on 2.4GHz maybe experiencing one of these signals crossing the field in that area.

Non-agile DSSS systems (like the Spektrum) are particularly vulnerable to these sources of interference because when the system links up, it's totally unaware that there's a potentially very strong interference signal perhaps just a few hundred yards away.

The best way to think of these beams is like a searchlight operating in daylight. Unless you're actually in the searchlight's beam, you wouldn't even know it was on but -- when your model flies into one it's dazzled and falls out of the sky.

It can be difficult to find the source of these data-links because they can be miles away (hence the reason they use high-gain antennas) and perhaps even beyond visible distance at ground level.

As I said -- the potential sources are manifold and this is just one.

We've lost DSM2-equipped models at our flying field (we have several WiFi repeaters and a number of suburban/school WiFi networks hidden by some trees) but not a single FHSS system has experienced any issues.

DSM2 will continue to work just fine for many lucky people but given the choice, when buying new gear for instance, I can think of no reason at all why you'd take the extra risk of buying 5-year-old technology when there's much better stuff available (at a lower price) from other suppliers.


There is simply not much use in using high gain antennas on 2.4ghz since it is line of sight and the horizon is only 17 miles away. If I were to design an industrial system I would use 900mhz since there is better propagation of the signal and you could use higher power. Most of the other stuff on 2.4 is WIFI and all of those I have seen use a simple dipole.
Even if there is a high gain antenna most likely you would be crossing the beam and you would just get a momentary glitch.
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Re: New FHSS from JR?

Postby QiW » Mon Nov 08, 2010 1:04 am

i was a dsm2 user (dx7)
i fly in an environment considered to have harsh RF .. underground cables and telco towers as well as sub power stations nearby
i have had a few planes just locking out on me .. retrieved plane .. orange light was solid (whenever the batt was not thrown out)
there are also other dsm2 users that flies with me ... they have one time or another experienced that too
well ... enough is enough .. most of us have migrated to fasst and have had peace of mind while flying
it is more expensive to crash a few models than to change your radio system IMO .. and thats not withstanding the number of hours spent building the model and potential damage to life and property
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Re: New FHSS from JR?

Postby avi » Sun Nov 14, 2010 2:21 am

Hello,
Thank you for all your reviews and advice.
I am very interested in your review of the new JR 11X zero. I am in the market for a new radio. I currently have a jr 388 on 40MHZ which I have used for 18 years. It is a fine radio but I am running out of model memory and the analog trims are sometimes causing some hairy takeoffs. I am also getting nervous flying on 40MHZ because of 2.4Ghz, frequency control is not so stringent as what it once was. I fly park flyers, slope and 1/4 scale power.

I was very close to buying the JR 11x, but I think I will hold out because JR seems to be in limbo with what to do with 2.4GHz and also telemetry. I do not want to use DSM2 so I have pruchased the Frsky 2.4 module (with telemetry) which will fit into the JR X11 (if and when I buy one). But I believe the 11X is not setup for telemetry so I would have to go for an external panel if I want to use the telemetry of the FrSky. I am just not sure if I want to fly the big stuff using FrSky. Anyone using FrSkY on big expensive models?

JR seems to be in limbo because they have just released the JR 7XG which is using DMSS and has telemetry. So it does not seem to be a good time to buy JR products since they do not have a clear sense of direction.

But if the JR 11X with DSMJ is good and there is some future upgrade posibility for telemetry then I will still go ahead and purchase the X11. I want to have a transmitter that I can both use for my 40MHZ receivers and for new 2.4Ghz receivers. So that is why I llike the modular system of the 11X.

So I am keen to hear your review of the JR 11x and if this is a good radio that is going to be reasonably future proof.

Thanks from Auckland
avi
 
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Re: New FHSS from JR?

Postby RCModelReviews » Sun Nov 14, 2010 9:15 am

There are three gas planes (a 30cc, a 50cc and a 55cc) on FrSky in our club and I also use it in my jets.

The modular version of the 11X is modular so it is future-proofed to a degree. The only downside of using FrSky in the 11X is that you'll only be able to use 8 of the 11 channels, but I haven't ever used more than 8 channels in a model anyway.

I'm pretty sure JR will be bringing out a DMSS module/receivers for the 11X very soon too and that'll offer the full 11 channels I'm sure.

I just saw some more documentation on DMSS and I was right - it is a constantly agile (FH) DSSS system, just like FASST, FrSKy and Hitec. Pretty soon, US JR/Spektrum users will be the only people still using "pick and stick".

Hope to get the 11X review up on the site this coming week.
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Re: New FHSS from JR?

Postby avi » Sun Nov 14, 2010 7:48 pm

Hi Bruce,
Thanks for your comments.
Do you think in future through a software upgrade, the X11 will be able to interface to a telemetry module (like FrSKY) and display the data on its own display, or is there some hardware missing in the X11 that will prevent this.

Regards from Auckland
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