invert0914

My Feedback: (17)

After loosing my beloved P-51 after many years of service I decided I had enough with Spectrum equipment. This was the second time I had a failsafe issue on two differant aircraft. I started to look deeper and try to educate myself on the technology and found this article from 2001 done for the walstreet journal. Inlight of the new rumers about Jr dumping DSSS technology and going to FHSS I looked even harder. Then in on another thread I found this reply to Jr's rumer which I have attached. The article about FHSS and DSSS technology was written by Texas Instruments after extensive studies about Airwave grid lock and the over use of 2.4. With that in mind it seems like a no brainer on why FHSS is better and why Spectrum requires all these satilite receivers. Its not about Brand wars as JR equipment has always been great. Its about the 2.4 technology they went with and there continues brand protection and endless upgrades they make to make it work.

Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern
known to both transmitter and receiver. Both the access point and client "hop" between frequencies based on the
same pseudorandom pattern, transferring a piece of data during each hop. Properly synchronized, the net effect
is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse Whenever interference corrupts the signal, the devices can resume their data transfer after the next hop to a new
frequency that is clear. Bandwidth drops each time the device encounters a blocked frequency. However,
interference does not break a connection. In the presence of interference, the connections do not fail and
throughput will degrade gracefully. Adaptive hopping (avoiding frequencies that are known to be blocked) can be
used to increase throughput.
The hopping pattern (frequencies and order in which they are used) and dwell time (time at each frequency) are
restricted by most regulatory agencies. For example, for operation in the 2.4 GHz band in the US the FCC
requires that 75 or more frequencies be used with a maximum dwell time of 400 milliseconds.
All FHSS products on the market allow users to deploy more than one logical channel in the same area. They
accomplish this by implementing separate channels on different, pseudo-random, hopping sequences. Because
there are a large number of possible sequences in the 2.4 GHz band, FHSS allows many non-overlapping
channels to be deployed in the same space.

DSSS transmitters spread the signal over a frequency band that is wider than required to accommodate the
information signal by mapping each bit of data into a redundant bit pattern of “chips� known as a chipping code.
The longer the chipping code used, the greater the probability that the original data can be recovered (and, of
course, the more bandwidth required). Even if one or more bits in the chip are damaged during transmission,
statistical techniques embedded in the radio can recover the original data without the need for retransmission. At
the destination the chips are mapped back into a bit, recreating the original data. Transmitter and receiver must
be synchronized to operate properly.
The ratio of chips per bit is called the "spreading ratio". A high spreading ratio increases the resistance of the
signal to interference. To an unintended receiver, DSSS appears as low-power wideband noise and is rejected
(ignored) by most narrowband receivers. A low spreading ratio increases the net bandwidth available to a user
Several DSSS products in the market allow users to deploy more than one channel in the same area. They
accomplish this by separating the 2.4 GHz band into several sub-bands, each of which contains an independent
DSSS network. Because DSSS truly spreads across the spectrum, the number of independent (i.e. nonoverlapping)
channels in the 2.4 GHz band is small. The maximum number of independent channels for any
DSSS implementation on the market is three.

FHSS Devices are More Interference Immune than DSSS devices
One of the clear advantages that FHSS systems have over DSSS systems is their immunity to interference. With
Figure 1, above, in mind, it is easy to understand the two attributes that make DSSS poor at rejecting outside
interference.
1. DSSS products spread their transmission power thinly across the spectrum. Transmitted power in any
specific segment of the band is low. As a result, low levels of interference can easily overpower the
DSSS transmission. FHSS products, in contrast, use relatively high power in a narrow segment of the
band for a short time. This allows the FHSS signal to overpower the interference in their segment of the
band.
2. Multi-channel DSSS products use statically allocated pieces of the band. Interference in any significant
piece of this allocated band will interfere with the transmission, possibly destroying it entirely.
All channels in an FHSS network hop around the entire 2.4 GHz band. Strong interference in a segment of the
band may hamper some of the transmissions, but FHSS transmitters - being frequency agile - will use the remainder of the band effectively. Users may see a decrease in throughput but the network will continue to
operate.
When interference occurs, it has a marked difference on the two different technologies. FHSS can overpower
and/or hop around the interference, experiencing, at most, some limited degradation. The DSSS signal, on the
other hand, can neither overpower nor avoid the interference.

Not a scientest but this article is interesting. 5 airplanes gone at my field this month all on Spectrum. I was one of them. It was not setup and its a P-51 that has flown all over the east coast including the nall for 4 years. I hate to say it but JR has lost me as a customer due to there inability to say sorry and there continuous brand protection cover ups. It is amazing how there is never anything wrong with the equipment sent back and its always the users setup.


ORIGINAL: Beavis


The JR/Spektrum detractors (who are really the only ones being over sensitive on this thread, by the way) forgot to mention that DSM technology is patent-protected, whereas frequency hopping has been around for decades - i.e., it’s a much older technology - and is in the public domain. This is why only JR/Spektrum can offer DSM; the others simply don’t have that option... The JR/Spektrum platform also happens to be the market leader in 2.4GHz by a very long margin.

Like most advanced radio systems, DSM is indeed more sensitive to power supply than the simpler hopping systems. Just be smart and careful when you power up your receiver and you will be worry-free, with additional safety features such as ModelMatch, which only JR/Spektrum can offer, among many other perks, exclusive and otherwise. I am among the ever increasing number of modelers using A123 batteries for all my onboard systems in internal combustion models. It is clearly the type of power to have nowadays.

As to JR moving out of DSM, here is a recent official statement issued by JR:



To Our Valued JR Customers:

During the recent BMFA Nationals, a new JR 7 channel radio system using DMSS was shown by our UK distributor. This system uses a technology that is incompatible with DSM2 in order to meet a market need where DSM2 is not available to JR. Unfortunately, several individuals made statements that JR finds very misleading and require correction.

JR remains committed to future development with DSM technologies and to our customers who currently own JR equipment using the DSM standard. JR will continue to manufacture, sell, and support DSM equipment in all markets currently allowed by agreement.

It is our goal that this communication clears up any questions about JR’s intentions and that JR remains confident in and committed to the future of DSM technology around the world.

We thank you for your continued support.

Kind regards

Mooney Takamura.
International Sales Manager
JR Propo



Happy modeling, whatever your choice may be.

onewasp

invert0914

Little sense in posting to someone who already has their mind made up BUT ALL the current systems qualify as DSSS.

Look it up, Futaba included. (In their FCC approval filing.)

Sorry you lost your Mustang but there are many of us Bob Violet included, (no he is not a personal friend) who have flown Spektrum since the date of its announcement in 2006 with no troubles what-so-ever.

Simply flawless flight after flawless flight. I'm referencing the radio not the pilot as 'flawless'

If you feel better with another set up, BMG.
That's one of the joys of this Hobby, you use the equipment YOU choose .

FHSS dates to the original Patent of 1942 .
Actress Hedy Lamarr and composer George Antheil, were the inventors. Yes, she was THAT smart !
A few years back Boeing celebrated Hedy Lamarr as "A woman of science."
No mention of her beauty or movie stardom was even made.

Plain frequency hopping was written about and tried much earlier, but that is much different than SS.

If you do not appreciate the antenna diversity then you really need to do more reading on SS.
Among many, there are; antenna diversity; spatial diversity; temporal diversity, etc. etc.

I am no SS expert but it IS an interesting read.

Wish you well with whatever set up you use, BUT remember it isn't at all like 72, 50, 53, 27 MHz.
Different animal entirely.

MikeL

My Feedback: (3)

Got a link to the original "walstreet journal" article?  It would be nice to put this in context, if it exists.

TimBle

all current FHSS transmitters employ DSSS as the core signal generation and transmission strategy.What sets the FH guys apart is that they do DSSS on every channel they hop to.FHSS is the more robust and superior system. That is truth and fact.

onewasp

If you are soothed by that fine.

I have yet to speak with an RF Engineer who will go that far .

For example XJet has stated that "on paper" such a case can be made.
However the advantage is slight and
tends to disappear in field circumstances .

I use what works for me
Suggest you do the same .

TimBle

soothing has zero to do with anything, fact, FHSS is a superior mode of transmission. I worked with and maintain contact with many ex colleagues who are RF engineers ans scientists. They tell me that if FH is available then the choice is a no brainer for interference free operation.Based on participation in projects with those people, it has been repeatedly demonstrated in many applications, that FH is vastly superior.

Silent-AV8R

I have a good friend that is, in fact, a RF engineer. He works for a company that does the security systems for shopping carts among other things. The system uses a 2.4 SS signal to lock the front wheels at a given point. Stops cart theft cold.

They use a hybrid DSSS/FHSS system similar to Futaba/Airtronics. He flies Futaba too. His comment is that if they won't trust stopping a shopping cart to a dual frequency system he sure as heck is not going to trust his $5,000 pattern plane!!

That aside, consider that the DSSS/FHSS system that Futaba uses have proven to be very robust using the two antenna diversity system.

The DSSS only system of Spektrum/JR has proven to be reasonably robust if enough satellites are used and the install is done with care.

But both types of systems are still subject to the problems caused by poor installations, loose wires, bad connectors, failing servos, and rotten switches. In fact, they make those issues all the more evident.

pilotpete2

While the debate goes on about which is more robust, all one has to do is compare a DSM2 setup on the bench with a FHSS system such as FASST. One clear, unarguable difference. Connect time. A system such as DSM2 must search for the transmitter it is bound to, with most receivers this search time is at least 2 seconds, or more. OK, you think that they fixed that with the "quick reconnect" software? Sure they did, but now when a DSM2 receiver loses the transmitters RF signal for a second or so, invoking failsafe, it also triggers the receiver to go into a search for the transmitter it's bound to, so instead of brownouts, we have fade outs. It seems that they traded a headache for an upset stomach, when they introduced "quick reconnect[]
I believe this behavior is what causes many of the lockouts that have been reported in the forums, and that I have witnessed at our field, where batteries and their charge state were not an issue. The FHSS systems will always connect virtually instantly, whether recovering from a voltage drop out, or brownout, or a loss of RF connection for a moment, heck, I can turn off my transmitters, and as soon as the transmitters screen comes up my FASST radios have a solid link, DSM2 cannot provide the instantaneous relink, except in the case of a power interruption of the receiver.
I know my post will ruffle some feathers, but I sincerely believe my observations are accurate. Please feel free to debate my assertions.
Pete

MikeL

My Feedback: (3)

What I find amusing about these sorts of discussions is that very few people with the necessary combination of education/experience/skill participate to any meaningful extent.  It's mostly "I bought this because I think/reasoned/love blah blah blah."  Lots of semi-informed gabbing, but very little real information.

aussiesteve

Regardless of the intricacies of the technology used. The true facts are those played out on flying fields every week all over the globe. (Even if something is made idiot proof , next thing that happens is someone else invents a better class of idiot - I know I do it all the time ).

I don't have access to all fields all over the globe but I do have access to information on the fields where I fly. Of the two major brands (Futaba and JR) the following statistics apply from the past 3 years.

The two brands are about equally used amongst the 126 flyers that I am aware of who have been using 2.4 at those fields.

JR / Spektrum 2.4 has been the brand involved in 16 cases of lost planes caused by unexplained "radio failure" during flight in the last 3 years.

Futaba has been involved in only one incident in the same time frame. (and that incident we are fairly certain was caused by a battery failure in the plane as the single 5 cell NiMh that was powering everything was found to be "flat" after the crash).

Unfortunately (for me - not for the sellers of JR/Spektrum as they made profit from my purchase of their equipment) I had purchased JR equipment (including a 12X Version 2 with the integrated electronics) and have recently retired that to "park flyer only" status. I have now had to spend a few thousand dollars more to go to the PROVEN more reliable brand. (This was decided upon after after losing planes myself)

I suspect the "high incident rate" brand is fine if you are ony flying a foamy park flyer or at least flying in the same flight envelope where most of those get flown. but outside that envelope, I suspect there is an issue with the technology (I am not an electronic "Techo" qualified to state exactly what that may be). There is certainly an issue with the satellite receiver connections.

Futabas technology has been used for quite a long time in some very critical areas of industrial automation.

I KNOW what works for us at the field I fly at.

Maybe we are all idiots but if one brand is better suited to us - then that is the brand we should use.

I know out of the 3 planes I lost (2 different TX's involved - the 12X and a 9XII (9303) with a conversion module) all 3 had dual battery supplies, one had a single satellite connection, the other 2 had 3 satellite connections. All electronics were still connected and working and the batteries were fully charged after 2 of the crashes. One was so badly destroyed that it could not be determined if anything was still connected at the time of impact - however the batteries remained charged. 2 were powered by unregulated A123's. one was powered by 5 cell NICd's. All had previously flown successfully and "Flawlessly".

Never lost a plane (due to radio issues) with the same brands of 36 MHz PCM of the same brand.

nonstoprc

My Feedback: (90)

I have witnessed one club member lost two planes guided guided by DSM 2.4 equipment. The sad thing is that he considered all 2.4G technology the same.

MikeL

My Feedback: (3)

This is where we get into funny speculation and are a bit out of our depth. Do you feel that a difference of perhaps several hundred feet and, say, a 70mph speed difference matters to radio waves that move at the speed of light? Maybe it makes a difference. I don't know. Do you?

ira d

It seems to me that the number of models lost to radio failure with JR/Spektrumis about 10 to one compared to allotherthe brands of 2.4 systems available
with maybe the exception of XPS. I know there are some that have been using Spektrum with good results but I feel there must be somethingto at leastsome
the problems reportedwith Spektrum.

MikeL

My Feedback: (3)

I have no doubt at all that there are more crashes due to Spektrum than any of the other major players.  They were the first out of the gate, and they didn't have the advantage of sitting back and watching what their competitors would choose to do.  It's a more complicated system, it has a more difficult binding process, and it's more sensitive to low-voltage situations.

ira d

I cant see where Spektrum is reallyany more difficult to bind than any of the othersystems and binding would have nothing to do with loseing the signal link once its bound
anyway, Also ifit is true that the problems are caused mostly by individuals operating the systemsthen why are they having such a problem with only Spektrum?

Another point also if Spektrum is indeed more complicated to the point that many users have problems with itthat they dont have with other brands thenI thinkwe could say
it is a flawed system.

MikeL

My Feedback: (3)

All I'm saying is that if you use it as it's intended, it works just as it's supposed to.  As for your question, please read my whole post.  I don't feel like rephrasing or typing it again.

invert0914

My Feedback: (17)

I agree with you that I know nothing more about the the systems other than what I have been able to find and read. The issue for me is I was on the same side of the fence as everyone else when it came to these threads. I need to go back and find the ones where I said to people its your setup dummy and not the technology. My mustang has had the same setup as my Scout for almost 3 years. Endless flights on both at Joe Nall and other events plus my field. The Scout went into failsafe there and I posted a vedio of this as it had an onboard camera. Of course it was recovered and no crash happened. Jr and a futaba rep all looked at my setup and said the setup was fine and could not find a reason for it. I am still flying it on the same setup with no issues to date. My Mustang at my local event went into failsafe at 120 plus and the engine ws the largest piece found less a few parts. The battery was at 6.2v under a 2amp load as I charged the flight before. Now my systems come back as checked ok. So its not my setup so quit saying its everyones setup like were are some kinda retard. Its very upsetting. It seems to me these threads keep popping up because for no reason the Jr equipment as a whole quits working then like magic works fine for a while and checks out ok. Good luck with the future. Im finished with them like many others. To each his own.

HunkaJunk

Amusing, this FHSS vs DSSS debate has been going on for years, long before we started controlling our planes with them.  I have heard all of this before, a long time ago.

My only problem with DSM is finding time to get another 3500 flights with it, which seems to be impossible lately.

impulse09

My Feedback: (3)

And just how much does one JR receiver and a couple of satellites cost? Is it more than a single Futaba 7 ch receiver?

HunkaJunk

I don't use satellite receivers, just the single satellite the RX comes with, and sometimes I change out the length of the connecting wire.

The people who say that DSSS is flawed either ignore the fact, or are unaware of the fact that DSSS enables the transmission of much more data over a greater distance than FHSS does.

I know enough about both of these systems to say that it is very difficult to legitimately claim one is vastly superior than the other, and certainly impossible to do so without leaving the door wide open for debate.

TimBle

not sure where you get the idea that DSSS enables more data over longer distance.what limits range in rc is visibility. all current systems are able to transmit and recievers (full range) are able to interpret the coded signals well beyond visual range. Far enough is far enough. Also, you forget that all systems use DSSS but the better systems employ continuous hoppingto other channels of the DSSS transmission.one brand in particular employs hopping through 36 channels continuously and with random selection of the next channel. Thats is vastly superior in any language

Silent-AV8R

Even if DSSS was capable of transmitting a greater amount of data, which it is not, it is a moot point since we use so little data for our models that the amount of data is irrelevant.

Here's a fun article;

http://www.sss-mag.com/primer.html#dsvfh

From the conclusions of that page:

MikeL

My Feedback: (3)

*sigh* He's talking about the underlying transmission concept, not FAAST vs DSM.

Funny how you're willing to apply that logic at certain times, but not others. Is that not the same as "works is works?" If that logic satisfies you, then why participate is trying to say that one system is so much better than another?

Is it just a game? Of course it is...

GerKonig

I am still using my old radio so I am on the fence. I read these threads because I know that sooner than later I will have to upgrade.

You just gave me the best 3 reaspons to go with Futaba:

Spectum is:
a more complicated system
it has a more complicated bindig system
and is more voltage sensitive

An this is said by somebody that defends Spectrum. For that reason I reallly believe you.

Gerry

MikeL

My Feedback: (3)

It's definitely all of those things, but "more" doesn't necessarily mean a lot. To me, the differences are largely meaningless. It's a lot like saying that McDonald's fries are healthier than Burger King's fries. Neither is healthy, even if one is a tiny bit healthier. Am I making sense with that? The difference in the downsides is small enough that most people won't ever be affected by choosing one over the other.

The one thing you should believe and take to heart is that brand loyalty is not the friend of the consumer. I buy whatever I think is best at the time I choose to make a purchase, and that's exactly what you and everyone else should do. If I were going to buy a system today, I'd probably buy the Hitec. I hate the exposed transmitter wire on the Hitec, but that's the only downside I see to it.

What would I really want? Something that doesn't exist yet. Spektrum's line of diverse receivers and their Model Match (now *that* is a great feature for anyone who flies multiple models each day, and it gets overlooked), and Hitec's telemetry and transmitter design. All of the mainline brands are reliable. They're all easy enough for me to use (but perhaps not for everyone, having read some people's "challenges").

The best thing to do is to decide what is best for you. Things like the underlying transmitting scheme mean absolutely nothing to the end consumer. (That's why threads that start like this one did are useless.) You've got to decide which feature set and price points are right for you. It depends on what you fly and on your habits. If you're a guy that tosses stuff in the fuselage without much care, Spektrum is not right for you. If you need many different types of receivers, Airtronics and Hitec aren't right for you. If you've got a lot of models, Futaba's receiver pricing might not be right for you. If you're sloppy at the field when it comes to flying a lot of models, Model Match might be something that'll save you a model. If you're sloppy about checking your receiver battery, Hitec's telemetry might save you a model. There's no brand that does it all right.

What they all do well is reliably guide our models. The one thing that too often gets overlooked is that they all work well. That being the case... get out and try the different cases. If a transmitter doesn't fit well in your hands, you won't be happy.