I  am considering using a Corona 2.4 g module on my JR XP 8103
DSSS System
http://www.r2hobbies.com/proddetail.php?prod=rcps21212_ds
FHSS System
http://www.r2hobbies.com/proddetail.php?prod=rcps21412_fh
and
http://www.r2hobbies.com/proddetail.php?prod=rcps21205

I came across this article :
http://www.arcelect.com/DSSS_FHSS-Spead_spectrum.htm

I am bit confused with this article which seems to say interference is possible  :
Spread-spectrum radio is good at dodging interference from conventional sources – (signals that stay in one narrow area of the frequency band and don't move. it doesn't  always do as well when there are other spread ,spectrum systems operating nearby, though. The more frequency-hopping transmitters operating on a band, the more likely it is that one or more of them will hop to the same frequency at the same time, garbling data that must be retransmitted. DSSS is better at resisting noise up to a certain point. However, if the combined interference throughout the band rises above a certain level, throughput dramatically drops-nearly to zero. Unfortunately, it only takes a few nearby FHSS systems to cripple a DSSS system. On the other hand, because a DSSS system is always transmitting on every frequency in the band, a nearby FHSS system may be unable to find any clear channel to hop to. In the presence of interference, FHSS usually degrades more gracefully than DSSS, but neither works well when competing at close range.

As I understood it :
FHSS hops frequencies hence if many FHSS Radios are flying together the chances of 2 or more radios getting on to the same frequencies is a strong possibility
DSSS : sends info along many frequencies in a band : hence if many FHSS are transmitting  around they can jam the info transmission channels of the  DSSS.

SO BASED ON MY UNDERSTANDING FROM THIS ARTICLE  DSSS IS BETTER THAN FHSS IF THE FIELD IS NOT CROWDED BUT A FEW FHSS OPERATING AT THE SAME TIME COULD CRIPPLE THE DSSS

This looks to be logical  but I thought 2.4 G is interference free  

Now  experts here on 2.4 G which is better for  a JR  DSSS or FHSS.

Sai

Sai - Without going into technical details, both Futaba FAAST and Spektrum DSM2 have been certified to operate about 40 of the same type concurrently. And those are numbers the manufacturers advertise.

When it comes to mixed usage, many fun-flys around the world report routinely having 10 or 12 aircraft in the air at the same time using a mix of both technologies. 

I do not know the numbers for the less widely used brands.  But interference is that last thing they have in mind.  In fact, I read many reports where people started participating in (I guess less regulated) funflys only after they got on 2.4, due to the peace of mind it offers.

Anwar ,
The reason I am asking these questions is I am looking at  buying a Corona 2.4 G for my JR.
Customer's  on Hobby City  gives it a 5 star review :
1) http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7381
2) http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7380&Product_Name=Corona_2.4Ghz_JR_Module_&_Rx_(V2_DSSS)


What surprised me is that  this article is by a wireless net working company and not  a RC company.

I think apart from general comments  a bit of going into technicalities is important  as  a company using RF transmission for a living claims that intereference is a probability . Hence there is a possibility that  some accidents using 2.4 G could be attributed to interference. The probability might be lower but the idea  that  2.4 g is interference free is not fully true.

Please don't mistake me I am not against 2.4 G quite the contrary I and thinking of adopting this technology .

I think some technical  engineers might be able to understand it better than me
sai

Quote from: anwar on July 11, 2009, 10:30:18 AM
Sai - Without going into technical details, both Futaba FAAST and Spektrum DSM2 have been certified to operate about 40 of the same type concurrently. And those are numbers the manufacturers advertise.

Please correct if wrong, I heard its 80 for car radios for Spectrum DX2.0 and DX3.0. ie you can have 80 cars running around at the same time, which is a literally impossible situation.

Of late I have been hearing too many issues on the spectrum radio specifically on range. They seem to work on nitro and electric well, but get issues on Gasoline models. Any feedback on that?

98% of rcuniverse guys suggest Futaba for larger models.

Quote from: mail4ajo on July 11, 2009, 10:42:01 AM
Of late I have been hearing too many issues on the spectrum radio specifically on range. They seem to work on nitro and electric well, but get issues on Gasoline models. Any feedback on that?

Do you mean SpeKtrum the brand/technology or the 2.4 speCtrum in general ?

Yes, Spectrum DX2.0 2.4ghz radio in particular. Lots of -ve feedback on the DX3.0 too, but only from gas engine users.

Anwar ,

Both FASST and DSM 2  are basically Brand Names of the basic system FHSS and DSSS respectively .

I have more or less decided to Go in for the Corona :
http://www.r2hobbies.com/proddetail.php?prod=rcps21212_ds

Will order it out next week .

But I still think some technical inputs on this article from members who know RF matters in the wireless  networking domain would help as  from a layman's point of view the authors of this article seem to have a point.

Sai

Quote from: rcforall on July 11, 2009, 10:39:57 AM
I think apart from general comments  a bit of going into technicalities is important  as  a company using RF transmission for a living claims that intereference is a probability . Hence there is a possibility that  some accidents using 2.4 G could be attributed to interference. The probability might be lower but the idea  that  2.4 g is interference free is not fully true.

Sai - If you want to get into technical aspects, take it from a guy who has a BTech in Electronics (although I moved to a different field pretty quick) I purposefully kept the technical details out.  There are other members here who have much more knowledge in the field (I know Rajesh/Rotorzone is one). 

If you fill up available frequencies progressively, anything will end up in interference.  That is why manufacturers put upper limits on concurrency.  It is the real life scenarios that are much more important than theoretical issues.

Quote from: rcforall on July 11, 2009, 11:23:12 AM
Both FASST and DSM 2  are basically Brand Names of the basic system FHSS and DSSS respectively .

That is common knowledge, hence I did not bother spelling it out.  Although, to the purists, Futaba FASST is more like "multiple channel frequency agile DSSS".

The only issue of Futaba FASST I know of (and I watch this carefullly as I trust all my flying to it), is when receiver temperatures are extremely high.  And that means keeping the receiver in direct sun on close to 50 Celsius days for a while (which is possible in places like Qatar in summer).  But simple precautions like keeping the model in shade or covering the receiver part with a piece of cloth solves the issue. And this is not an issue during flight due to various orientations and airflow.

Spektrums (which is used in JR also) do lose binding (pretty rare, and even when it happens, it is at the beginning of the flying session, so it is caught on the ground itself).  Futaba FASST is much more immune to this.  Not sure about the range issue on gas engines for Spektrum/JR, need to research that a bit.

Thanks Anwar that is more like it  

This explains to a layman like me the  situation more clearly .
As I have said right at the start of this thread I am confused as  reading something like this gives a different picture from what we hear .

BTW since you say saturation and interference is possible can it happen that  there  are just 2-3  transmitters of 2.4 G operating on a given field and two of them during the hopping stage get on to the same frequency momentarily , the possiblity may be remote but is it possible ?

Sai

Thank you Anwar, that was a satisfactory explanation, I have a DX7 and keep wondering if I'm ok with it and sometimes wonder if it was worth the investment. and if 2.4 is the way to go??
Issues are everywhere and how you deal with it is more important than how you could be prey to it!!!
thanks.

Hello Sai,

Do not worry about the interference issue in 2.4GHz. Any communication system operating on probablistic nature (like FHSS) will have "collisions". The communication protocol will be designed such that it recovers from these collisions which occur only for a fraction of a second.

So, when you have FHSS around there is a strong possiblily of FHSS colliding with a DSSS or with another FHSS but the systems will recover quickly withouh any noticable effect. IOW, if a collision occurs you loose control of your model say for 5 -10milli Sec... Thatz too small a time to make any noticable change in your flight pattern - Applies even for 3D/4D moves.

-Ismail

Quote from: rcforall on July 11, 2009, 12:08:37 PM
BTW since you say saturation and interference is possible can it happen that  there  are just 2-3  transmitters of 2.4 G operating on a given field and two of them during the hopping stage get on to the same frequency momentarily , the possiblity may be remote but is it possible ?

If you are worried about couple of Spektrums being used at the same time as couple of FASSTs, let me try to put it in non-technical terms as much as possible.  What should happen is that both the Spektrums will pick couple of channels each and transmit on them continuously.  Now if two FASSTs are turned on, they will start jumping within a range of channels, changing channels every 2 milliseconds. So it is possible that they will land on the channels that is being used by the Spektrums.  But the Spektrum receivers ignore this, as they respond only to the packets if the transmitter guids match the ones they are bound to.  And in the next 500th of a second the Futaba signal moves off to some other channel, and life goes on. We cannot call that interference, this is part of the conditions under which they are designed to operate.

This is a simplistic explanation for why many Spektrums and FASSTs work fine together in mega funflys where multiple radios are on, without any issues.

Now what will happen when 25 Spektrums and 25 FASSTs are turned on at the same time ?  Will that cause the receivers not to receive enough clean packets to provide glitch free flight, I am not sure. I can't find references for such a test, yet.

Quote from: FlyJoe on July 11, 2009, 12:54:30 PM
Issues are everywhere and how you deal with it is more important than how you could be prey to it!!!

Yes, what is more important is common sense items like ensuring appropriate battery power for the TX and RX.  If those things are taken care of, 2.4 is pretty much as safe as it can get nowadays.

Thanks guys some input on which is better DSSS or FHSS.
I am thinking of using the Corona  Module suitable for JR.

can anyone comment on Assan Vs Corona which is better.

Sai

Quote from: rcforall on July 11, 2009, 01:35:57 PM
Thanks guys some input on which is better DSSS or FHSS.
I am thinking of using the Corona  Module suitable for JR.

If you look on the forums (just chatter or deep technical discussions), you will see that most people agree that FHSS is superior technology (and the Futaba FASST is a pretty good way that technology or similar technology is delivered to end users). 

But it is not just the theory/technology, the "implementation" is just as important (the heat issue for FASST is a result of incorrect choice of components/tolerance, it has nothing to do with the technology, and Futaba may fix it in later revisions). 

Ismail,
Thanks for what you said but knowing you a re familiar with the 2.4 G technology which is better :
1) FHSS or DSSS
2) Assan or Corona

Sai

Hello Sai,

If you ask me about the technology, I would prefer FHSS as there is a lower chance of collision due to narrow (freq) band usage at any given instant. Furthermore, FHSS can also recover if there were collisions. BTW, the Wi-Fi LAN and some military communication devices uses FHSS for transmission. This should give you a fairly good confidence on the integrity of FHSS transmissions.

OTOH, DSSS is also good but the (freq) band usage is much wider than the FHSS. There is more chance of DSSS being hit by an unwanted disturbance. However, DSSS has a feature of automatic error recovery where the received data can be corrected by the receiver itself. Lower retransmit requests from receiver.

For a normal aeromodeller, both technologies are fit for the purpose.

On Assan and Corona. I have no idea as I have not used any of em. I have just ordered an Assan module & RX to try it out. The choice is mainly due to lower cost of Assan RXs and nothing to do with the technology.

-Ismail

Thanks Ismail ,
Coming from you I will go for FHSS.
I am seriously thinking of Assan as well because of the very same reason.
They have some economical 4 channel receivers that  can be used in small foamies and parkflyers .

BTW I checked the Assan Specs. no where does it say if it is FHSS or DSSS. The reply by Assan on  this question is this :
""""
in 2.4GHz system, there are not only FHSS and DSSS, there have some other digitally modulated intentional radiators.we are the "others",i promise its abide the FCC and EU rule in 2.4GHz radio system., the 2.4GHz chip maker localed in EU and sold all around the world
""""

http://www.rcgroups.com/forums/showthread.php?t=723343&highlight=fhss

Post Number 14

So Ismail what is this new  angle 
Any idea since you have also ordered an Assan module

Sai

Sai -  You should really read the Hobbycity discussion forums about Corona.  They had some significant quality issues with Corona/Turnigy stuff, and were coming out with an updated version.  It may all be fixed by now, but do your research if you are going for Corona.  When I looked at it a few months ago, it looked like a case of "you get what you pay for" in terms of manufacturing/parts quality.

Assan looked more like DSSS from what I read, but then it might be similar to the Futaba case where some people classify it more as "channel agile" DSSS.

Sai,

I am not sure of what technology Assan uses. There are quite a few communication schemes that could be used over 2.4Ghz. FHSS and DSSS are more widely used. May be Assan is using a properiatery protocol.

My main reason for going for Assan is because of their cheaper receivers. For me, I don't require a bullet proof system - a few mill second signal loss is OK...  . Further, Assan modules have received a good feedback.

-Ismail

It would be cool if anyone who has free time to start integrating/summarizing these kind of discussions about radios in the Wiki   

http://www.rcindia.org/wiki/Radio_Transmitters

Some one with knowledge  not an Anadi like me.

Sai

That is the beauty of a Wiki, even if something is wrong, someone else can fix it 

In fact I am quite tempted to try this out on one of my transmitter's  as it looks like  a  thing to have :
http://spadworld.net/forum/viewtopic.php?t=16480

Sai

Hey guys thanks to Chan I should be getting my Assan Module within this week.
He located one lying spare in chennai

sai