Corona module 2,4 DSSS for FUTABA 35Hhz ????????

[luisluis]

Hello,


In Hobbycity store have New Corona module 2,4 DSSS for Futtaba, Is Ok?or Futaba nedd FHSS, I don't undertand. Anybody can explain me this? Can i buy it in DSSS for Futaba? Which is the best DSSS or FHSS?.


Thank you

[Toumal]

If the choice is between Corona and Futaba, I'd take Futaba. If the choice is between DSSS and FHSS, I'd take FHSS.

[WinginIt]

	Quote: Originally Posted by Toumal
	If the choice is between Corona and Futaba, I'd take Futaba. If the choice is between DSSS and FHSS, I'd take FHSS.

I believe there are a lot of plusses to DSSS (direct sequence SS) over FHSS (frquency hoping SS) although both seem to be reliable.
We tested the Corona 2.4 (DSSS) (in a Futaba 9C) with the CR8D receiver today and could not get it to glitch at over 1000 meters with the feceiver mounted in the most undesirable place (in the midst of servo extention wires, etc). Then we flew it till it was barley visable (couldn't even guess how far it was).
Seem to be a very reliable system.

[Mithrandir]

	Quote: Originally Posted by WinginIt
	....I believe there are a lot of plusses to DSSS (direct sequence SS) over FHSS (frquency hoping SS) .......

Really??? Can you explain what they might be?

thanks

[WinginIt]

My first sentence in my previous post was not worded very well. There are not "a lot" of plusses.

I am by no means an expert in this area I am just going by what I read:
- Direct sequence spread spectrum, also known as direct sequence code division multiple access (DS-CDMA), is one of two approaches to spread spectrum modulation for digital signal transmission over the airwaves. In direct sequence spread spectrum, the stream of information to be transmitted is divided into small pieces, each of which is allocated across to a frequency channel across the spectrum. A data signal at the point of transmission is combined with a higher data-rate bit sequence (also known as a chipping code) that divides the data according to a spreading ratio. The redundant chipping code helps the signal resist interference and also enables the original data to be recovered if data bits are damaged during transmission.

Direct sequence contrasts with the other spread spectrum process, known as frequency hopping spread spectrum, or frequency hopping code division multiple access (FH-CDMA), in which a broad slice of the bandwidth spectrum is divided into many possible broadcast frequencies. In general, frequency-hopping devices use less power and are cheaper, but the performance of DS-CDMA systems is usually better and more reliable.

Spread spectrum first was developed for use by the military because it uses wideband signals that are difficult to detect and that resist attempts at jamming. In recent years, researchers have turned their attention to applying spread spectrum processes for commercial purposes, especially in local area wireless networks.

I am only now realizing there might be different openions.

[Tin man]

This thread is getting amusing. LOL



--
Mike

[Kiwi]

I picked up a Corona system a few weeks back and it quite simply does not work. The system binds OK as per the book but from the 8 channels only four actually function.

Now the problem may not be a Tx or Rx fault, rather it seems Corona have jumped from DSSS to FHSS and there seems to be no way to tell what Rx or TX you have. I have a feeling I might have one of each If there is a way to tell what system you have please enlighten me. I wrote to Corona explaining the fault and have yet to get a reply.

I put the Tx module over my scanner (Wi Spy) and it shows the transmission as hopping all right but only on three channels and not the entire spectrum as I would expect. Seems like Corona need to clean up a few things to get it right.

This weekend we tested the new ASSAN system as well. It is DSSS and works like a charm. I have not had the chance to run this setup over the scanner but will do so in a few weeks time. However for what its worth it really looks like ASSAN have done a lot of good work on their system as it is glitch free, we tested it to out of site range and seriously its A++++ in my books.

[WinginIt]

In my case (Futaba 9c) the TX module is DSSS and the correct receiver is the CR8D. Corona for JR is FHSS and the correct receiver should be CR8F. From what I understand the "D" at the end of the receiver model stands for Direct and the F for Frequency Hopping.

[Darklighter]

I would never buy a CORONA 2.4ghz TX Conversion set. You get what you pay for with these units. The failure rate seem to be very high.




2.4GHz Radio Control Explained

JUST HOW DOES SPREAD SPECTRUM RC REALLY WORK?

If you've got, or you've been thinking of buying, a 2.4GHz spread-spectrum RC set then you'll probably be keen to understand exactly how it works, and hopefully this article will help you do so.
First, a few words about older "narrowband" RC systems...
Traditional narrow-band RC systems on anywhere from 27MHz to 72MHz are fairly easy to understand because they work just like your regular AM or FM radio - sending out a signal that is picked up by the receiver and then sent to the servos.
Unfortunately, just like regular FM broadcast radio, these RC systems require a frequency all to themselves if they're going to avoid interference with each other. What's more, it doesn't take much to disrupt a regular narrow-band signal. A noisy thermostat or electric drill can often cause massive amounts of electrical interference when listening to an AM broadcast and FM isn't always that much better.
But manufacturers of spread spectrum (SS) radio systems are claiming that you need never worry about being shot down by other fliers and that all 2.4GHz systems can get along in harmony, despite apparently using the same frequencies.
So how can that work?
Well to explain this, I'm going to use a series of illustrations that I call "the freeway analogy". Using these diagrams and explanations, I will do my best to convey the complex world of spread spectrum in a form that most people can get their brains around. Of course in doing this I've had to take a few liberties with the details but these are not important.

Which Flavour of Spread Spectrum?

YES, IT COMES IN DIFFERENT FLAVORS

Before I launch headlong into a detailed explanation, it's worth pointing out that there is more than one flavour of spread-spectrum.
The first and most common type is what we call Direct Sequence Spread Spectrum (DSSS). This involves the transmitter and receiver staying within a fixed part of the 2.4GHz spectrum.
The second type is called Frequency Hopping Spread Spectrum (FHSS) and involves having the transmitter and receiver constantly changing their operating frequency within the alowed limits of the 2.4GHz band.
At the present time, only Futaba and Airtronics use FHSS, the remainder using DSSS.
And right now I can year you asking "which flavor is best?"... to which I have to say... neither and both.
Or, in other words, neither solution is best all the time, there are benefits and drawbacks to both, as you will see. However, it's safe to say that in theory, the Futaba FASST system does give the best of both worlds because it is not only FHSS but also DSSS.
But first, let's see how a traditional "narrowband" FM RC set works on frequencies such as 27, 35, 36, 40, 41 or 72MHz.

How do traditional RC systems work?

NARROWBAND FM/PCM RADIO CONTROL

Ever since the first radio control systems for models were built over half a century ago, the technology has been "narrowband".
Narrowband refers to the amount of space that signal takes on the spectrum of available frequencies.
Today's FM/PCM radio control systems operate on a tiny sliver of space on relatively low frequencies (27, 35, 36, 40, 41 or 72Mhz).
This tiny allocation of bandwidth for each RC channel creates a number can be likened to riding a bicycle down a narrow trail and the same problems apply:
Firstly, you can't ride very quickly simply because it's such a squeeze to get past the bushes and fences either side of your trail. In radio terms this means you can't send the control information between transmitter and receiver very quickly.
Secondly, if you run into another cyclist on that narrow track, chances are that you'll both fall off and get hurt. In radio terms it means that almost any other signal on the narrowband frequency you're using will result in interference (glitches or lock-out).
Clearly this isn't the best situation for controling a potentially expensive and sometimes dangerous radio controlled model but, with careful channel management, it has served us well for decades.

Distributed Spread Spectrum (DSS)

SPREAD SPECTRUM EXPLAINED

Distributed Spread Spectrum radio can be likened to a multi-lane freeway where your car seems to appear at random in different lanes. In fact, it appears and disappears so quickly that it almost appears to exist in all lanes at the same time.
In radio terms, the transmitter uses a wide spread of frequencies to send data to the receiver, rather than the very narrow band of frequencies used by the older narrowband RC sets we've seen up until now.
So what's the point in spreading yourself so thinly?
Well if you stop and think about it, if your "DSS" car encounters another on the freeway, it won't have very much effect. Your own vehicle won't be blocked because it will simply continue past when it suddenly appears in another lane which isn't blocked.
In radio terms, a single (or even quite a few) other transmissions won't have much effect on your RC system because they'll only block a tiny amount of the signal being sent. In fact, unless the freeway is almost completely blocked, at least some of the signal from your transmitter will get through to deliver your control inputs to the receiver.
Even better, if another DSS transmitter (or even several more) is operating on the same channel, it is also unlikely to interfere because it'll be jumping lanes in a different sequence and at a different rate.
So in a DSSS system, the last SS stands for Spread Spectrum and the first two letters stand for Direct Sequence. This relates to the order and frequency at which your vehicle moves between the lanes.

How DSSS Handles Interference

THE BATTLEFIELD ANALOGY

Another way to help you understand how a DSSS system avoids being "shot down" by interference is the battle-field analogy.
When an army goes into the modern battlefield, they're usually ordered to "spread out" -- and that's exactly what DSSS does, it spreads your transmitter's signal out over a much wider area than is the case with FM/PCM gear.
Just as on the battlefield, it's much harder to kill an enemy when they're spread over a wide front, so it is with a DSSS radio signal.
The chances of any single rifle-shot actually hitting a soldier on the battlefield is significantly reduced when they're widely spaced across the whole front. With DSSS, your radio signal is similarly spread very thinly across the radio spectrum and thus virtually immune to enemy fire, unless that fire is very intense.
By comparison, a closely grouped army of men can be decimated in moments by a single mortar shell or burst of machine-gun fire. That would be the equivalent of your old RC gear being shot down by interference or another transmitter on the same frequency being turned on while you're flying.
So what if someone turns on another DSSS system that uses the same channel you're already on?
Well because DSSS spreads your troops so thinly across the battlefield, there's plenty of room for another platoon from a totally different army to run between the ranks without the two colliding. This is why multiple DSSS systems can co-exist on the same channel without interfering.
Which radios use DSSS
Of the currently available 2.4GHz spread spectrum systems, all use some form of DSSS but others, such as the Spektrum/JR and Futaba FASST systems use other techniques to offer even greater protection from interference.
Several other systems that have gained a small following are those from XPS, Assan and iMax. These also use DSSS but appear to have no effective way of coping with the kind of crippling interference that might leave the other systems unaffected.

How do FHSS RC systems work?

FREQUENCY HOPPING SPREAD SPECTRUM

Frequency Hopping Spread Spectrum radio systems work by constantly hopping between a number of frequencies.
If you've just read the description of how DSSS systems work you're probably wondering "what's the difference?"
Well, whereas the DSSS system is like a car that repeatedly appears and disappears on various lanes of a freeway, at such a rate that it almost appears to be everywhere at once, a FHSS system effectively sees your car not simply jumping a small distance to a nearby lane, but all the way to a completely new freeway.
In radio terms, this means that the frequency sent by the transmitter doesn't just jump around within the chosen operating channel but actually jumps between a whole range of different channels.
It can be seen that, at least in theory, the FHSS system should be even more immune to the type of congestion that would cause problems with a DSSS system. That's because although nothing may get through while it was using a very congested freeway, the hop to a less congested one would allow the normal transfer of data to resume.
Under normal circumstances a FHSS system hops between a fixed number of channels in a repeating random sequence. When multiple FHSS systems are used together, the random anture of the hopping sequence means it's very unlikely you'll find multiple sets trying to use the same channel (freeway) at

How FHSSS Handles Interference

THE BATTLEFIELD ANALOGY

In a pure FHSS system, the troops are all closely grouped together as was the case with an old narrowband system but, because they're constantly jumping from battle-field to battle-field, the effect of enemy fire in any particular field is minimal.
Imagine that the whole army is teleported onto a battle-field and then, before you realise it, telported away to another. Clearly this makes a FHSS system a hard target for interference to hit.
However, the FHSS systems we're seeing used in radio control systems right now are a blend of both DSSS and FHSS. This means that not only is the signal spread across a whole channel but it also hops continuously from one channel to another.
This means that an FHSS system is an incredibly difficult target for any interference to hit -- and when you're flying RC models, that's a very good thing.
Which radios use FHSS
Right now, only two readily available 2.4GHz spread spectrum radio control systems use FHSS. These are the FASST radios from Futaba and the Airtronics offerings.

Belt and braces

EVEN MORE PROTECTION AGAINST INTERFERENCE

By now you've probably realised that spread spectrum technology offers some very clever ways to reduce the effects of interference and allow many different radio sets to operate simultaneously without the need for a frequency peg.
Thanks to the way these systems spread their signals thinly across the 2.4GHz band and thanks to the way some of them hop around so as to remain a moving target, it takes a very strong interfering signal to have any effect.
I've already explained that, at least in theory, the Futaba FASST system is probably the most bullet-proof SS system on the market, but the JR/Spectrum offering has also made it self doubly resistant to interference -- not by hopping all over the place but by adding a redundant channel.
As previously outlined, a DSSS system *can* be knocked out if the strength of an interfering signal on that channel is strong enough -- so JR/Spektrum reduces the risks by using two channels at once.
This means that even if a very strong interfering signal appears on a channel being used by your JR/Spektrum set, you won't lose control, and that's because the second channel on its different frequency will almost certainly be unaffected.
Reputable mnufacturers realize that their systems may be in control of very large, expensive and potentially dangerous models so they try to allow for as many contingencies as possible. Futaba uses constant frequency hopping, JR/Spektrum uses a backup channel (a tactic known as redundancy).

What is diversity?

Another important aspect of 2.4GHz spread spectrum radio control systems is something called diversity.
Diversity is required because the radio signals at 2.4GHz behave quite differently to those we're used to on lower frequencies such as 72MHz.
Whereas the old narrowband frequencies will pass right through most objects such as houses, trees, fences, and model airplanes, 2.4GHz behaves much more like light, being either absorbed or reflected by many parts of the environment.
This absorbing and reflecting of the 2.4GHz signal results in occasions when the receiver antenna by be shielded by some part of the model, or may even be subject to the kind of ghosting that used to be seen on old TV sets when the signal was reflected by trees or buildings (called multi-pathing).
The effects of shielding and/or multipathing mean that it's quite possible the receiver will be unable to hear the transmitter clearly enough to extract the data being sent.
The simplest (and best) solution to this problem is to use more than one antenna and/or more than one receiver in your model. By mounting these antennas or receivers in different places (even just an inch or two appart), one can take over if the other is unable to get a clear signal.
The JR/Spectrum system allows for multiple receivers, up to four or more and some of these receivers have mutliple antennas. This is surely the ultimate diversity setup. On very large models, you can be absolutely sure that there's no chance of shielding or multi-pathing by simply increasing the number and distribution of receivers within the plane.
The Futaba FASST system uses two antennas mounted on the one receiver. In theory this isn't as good as the JR/Spektrum option but in practice it seems to work perfectly adequately.

Summary by brand

COMPARING 2.4GHz SPREAD SPECTRUM RC SETS

I'm sure the big question most people want to know is "which SS system is best?"
Well the truth is that the big-name sets (JR/Spektrum and Futaba) are both pretty decent offerings that have a growing record of reliability and performance.
Of course if you ask enough people you're bound to find someone who has had problems with almost any brand of radio, and these new 2.4GHz systems are no better.
It's well worth remembering that we're still dealing with first-generation equipment here so there will inevitably be teething troubles and issues that need to be addressed. Indeed, both JR/Spektrum and Futaba have already faced some of these problems but things now appear to be quite stable.
I don't think anyone will be disappointed by purchasing either of these big-name brands so the selection criteria will most likely be based on your budget and the type of models you fly.
However, there are alternatives to the "big two" brands, although they remain less proven.
The XPS module-based 2.4GHz system is a single-channel non-hopping DSSS system that offers neither antenna nor receiver diversity.
Although many people have reported excellent results with this system, it is worth perusing the various discussion forums around the Web to read about the issues others have had with XPS.
Perhaps one of the biggest problems is not so much the technology as the man behind the product and his approach to marketing. Right from the start, the XPS system has been grossly over-hyped and under-delivered.
There are a growing number of former fans of the system who now freely air their disappointment, usually after losing models to unexplained lockouts or other failures.
Another second tier offering is the module-based Assan 2.4GHz system out of China, which is another DSSS non-hopping system. However, Assan do offer receivers with antenna diversity and there have been few reports of problems to date.
Another new entrant to the scene is the iMax 9X 2.4GHz RC system out of China.
Unlike XPS or Assan, the iMax system is a complete radio, albeit the transmitter can be used on 35/72MHz or 2.4GHz simply by swapping modules. It is far too soon to establish the robustness, reliability and ultimate perforance of the iMax system yet as it has only just started selling. (but look for a review soon on RCModelReviews.com).

So which is best?

As I said before, there's no absolute "best" 2.4GHz system because everyone's priorities are different.
If you want a system that offers a wide-range of different receiver sizes and capabilities with maximum diversity on very large models then the JR/Spektrum offering has much to offer.
However, if you're looking for a "technically superior" system, it's hard to go past Futaba's FASST. Unfortunately, at this time there are not a lot of receiver options and Futaba has been very slow on delivery of some options.
If you're prepared to be an early-adopter then the new wave of low-cost offerings out of China may be worth a try. Check their specifications carefully though, and also keep an eye on the various discussion forums around the web. As first generation products they may have some as-yet undiscovered problems or limitations.
About the only system presently on the market that I would be hesitant to recommend is XPS.
As I said earlier, many people have had no problems with this system and it has worked perfectly for them. However, from a technical perspective, too many of the system's wild claims are unable to be substantiated by the manufacturer and the growing number of dissatisfied customers must be a concern worthy of consideration.

http://www.rcmodelreviews.com/

[WinginIt]

Darklighter,
I am very impressed with your knowledge of the 2.4 systems. Thank you for posting this information.
In your opinion...... Is your concern that the China systems are more likely to “fail during use” even though they seem to work fine initially?

This would be something I would be very interested in since the Corona system we have been flying with seems to be doing everything perfectly.

Appreciate your input.
Doug

[Darklighter]

Doug,

I cannot take credit for the above post. I included a link from the site I copied it from. There has been several websites across the web that have posted failures using the Corona systems due to there cheap components. The products were taken apart and the problem was isolated to this. I guess you get what you pay for. I’m sure there are good ones and bad ones. What is your airplane worth? And where is the weakest link.

[WinginIt]

Thanks for the info.

I will let you know if we develope any problems as we will have 4 planes 1 Heli up soon with the Corana 2.4 for Futaba systems since they are ordered already.

Out of curiousity, where are Futaba and JR's systems built. I assume they are American Built. I know a lot of people who fly 2.4 Futaba and JR and I only personally know of one of them failing so far. All my planes have flown Futaba TX and RX and Hitec servos and I have always found them reliable. Took me a long time of watching my fellow pilots fly their 2.4s before I decided to try it. Wish me luck.

[Costas]

Here is a good link which explains some of the workings of DSSS (with some diagrams) - Just skip over the first few paragraphs if you are not into mathematics.. The rest of the article is reasonably simple to follow without getting too technical.

DSSS Introduction

Its not easy to compare FHSS and DSSS systems on a level playing field as basically they are two different beasts. Depending on the type of interference you can easily show how either one performs better over the other. Simple statements such as one is technically superior than the other are not quite true as it will depend on the circumstances. For any pilot flying RC either with FHSS or DSSS systems, both will far exceed the level of performance we require.

BTW I had been involved with some testing of early Corona DSSS and FHSS gear - basically their RF design wasn't too bad but their firmware was hopeless when it came to the standard RC features we expect from JR/Futaba and the like. It had a few bugs and some of the hardware was faulty out of the box.

I had the impression that the 2.4GHz Corona gear was designed by a bunch of engineers with very little RC background even though I don't think that is the case since they do have good experience in the 72MHz Rx dept.

Some JR is manufactured in Japan (eg 12X) and some in China. I think most Futaba is now manufactured in China nowadays. Nevertheless just because its manufactured in China does not mean its no good - It all comes down to what quality the OEM has specified for the production.

[WinginIt]

The Corona's we are and will be using are the V2 (version 2). Hope we do not run into poor quality since the price is very affordable.

[Tin man]

What exactly made you choose Corona in the first place?

Earlier you hinted you were apprehensive about moving into 2.4. Just seemed odd that you'd then choose Corona. Kinda like worrying about buying a reliable new car and then choosing a Yugo .



--
Mike