RC India

I have  a very basic question on 2.4 g which might sound a bit stupid but is something many of us here  might find useful :

If 2.4 G is  a free frequency  with no restrictions on use then  wont it be over crowded  and full of interference like 27 Mhz AM as so many devices are operating on this band.

The reason I am asking this as well is because when I was discussing with a a user from europe  recently he said that the range of a 2.4 G Tx and Rx this is what he had to say :

" In the French countryside I was flying out to 450m without any problems, but in the city here in Shenzhen I can’t get more than 10m range due to the 2.4Ghz interference "



Look forward to comments from the techo's here cause we all talk of " peace of mind with 2.4 G ".

Let me see how I can explain this clearly.

Futaba FASST is basically a frequency hopping system.  It does not transmit continously.  Rather, it transmits in bursts!! So there is a pulse every 10 ms.. Each pulse is coded with a randomly generated code and recognized by the Rx. If there are 2 pulses A and B, A would have a code and would be recieved by the Rx, B would be recognized by the code carried by A.. So the previous pulse tells the Rx on what pulse should be accepted next!! In fact, pulse A tells the Rx that pulse B is next.  So the Rx ignores all other signals except B!! This is how the cycle goes.. And not to mention that pulse A would be in one frequency and pulse B would be in another frequency! So even if there is intereference in one frequency, it would be for a matter of 10ms which hardly matters! Before you even know it, you would be onto the next pulse!!

The only problem occurs, when there is a mass jam of signals and no signal is able to reach the Rx, but to factors like carbon fiber attenuation or total disturbance of all frequecies due to unknown factors etc., then the Rx unbinds from the Tx!!  That is, after signal A, if B,C,D etc cannot be received, then the Rx unbinds leading to an unevitable crash.  But this is practically not possible unless it is user error on placement of receiver!!

Hope this explains things to a certain extent!! Am not really an electronics guy, but tried explaining as best as I could!

- Chan

Chan .
Thanks for the explanation , what I am looking for is the  part highlighted in bold .

It appears from the comment of this manufacturer and user of 2.4 G systems that there is massive interference in and around cities or populated areas .

In fact in the case of  UAV applications where the Auto Pilot  OR Video down link  operate on 2.4 G I have myself observed that you both these cannot be 2.4 G there is a clash . Hence using a 2.4 G radio is not advisable .

This fact is highlighted in RCG and other FPV forums time and again  where they clearly say if you use a 2.4 G FPV linkage you cannot use Radio's lik Dx 6 i or FASST .
Note the last few lines of post 1 here :
"""""""""""
For a typical RC pilot flying visual, radio transmitter is always pointed more or less towards the plane (but you can not rely on your muscle memory in a rare cases when model flies behind a tall tree or barn etc. because unlike 35-50-72MHz the RC link will be lost) but this microwave effect combined with shorter range than a standard 35-50-72MHz systems makes it very unsuitable for FPV applications (except FPV park flyers etc) and rather useless if your FPV-TX is also using 2.4GHz.
"""""""""""""
http://www.rcgroups.com/forums/showthread.php?p=12366897

So logically if 2.4 g can survive any interference then it  should  not have problem with other functions of an FPV or UAV working on 2.4G.

So what we are talking here is not 2.4 G radio to 2.4 G radio clash but clashes with other stuff on 2.4 G as well apart from Radios for flying .

I am confused  ???
sai
 

The video tx problem is different from the other issue. The video tx can overload the front end of the RF receiver and hence no signal will be received. This is not specific to 2.4GHz, it can happen at any frequency. What happens is that the front end RF transistor gets driven to saturation region by the strong signal. In saturation region the transistor no longer works as an amplifier and hence no signal get through that the later stages can filter.

Spread spectrum is less susceptible to interference, do not assume no interference. For  spread spectrum systems the spreading code in each tx has to be orthogonal to not interfere with each other. This is possible when one manufacturer makes all the transmitters. When there are many manufacturers(not just RC, any 2.4GHz wireless tx)  there is no guarantee that their codes are orthogonal and hence they can interfere with each other. But the good thing is even if codes are not orthogonal, it doesn't result in  a total loss of signal, but degrades slowly.

Hello uncle,

What I see in your post is not interference alone but also loss of control.  I am at a loss to understand why two or more 2.4 systems cannot be used in the same application!! But I do agree with the line of sight issue.  2.4 starts losing range when it is out of the line of sight which is very unusual for our kind of flying!! Moreover, even carbon fiber and other stuff block the signals from the Tx to the Rx.  But as with technology, this is one of the known disadvantages of 2.4 which is of course not perfect.  Better suited for the regular club flier who does not wish to bother around with frequencies.  Moreover on a straight line, DSM2 Rxs have been known to have a range of 1.5miles plus!!  For FPV purpose, even traditional PCM systems will not have a range of more than a mile unless you have external boosters for the transmission!

Of course, 2.4 systems cannot clash for more than a few milliseconds as explained in my previous post!! That few milliseconds will not matter even when you are low down on a tail touch..

But of course, I would leave it to Ismail and Anwar or more electronically savvy guys to comment on this too!!

- Chan

Well, I have not used a FPV system before and I have just entered the 2.4G band wagon with the Assan module. So, take my comment with a grain of salt.

By reading Sai's post I infer few things:

1, 2.4G TX/RX link degrade as there are obstructions in line of sight.
2, 2.4G TX/RX link degrads when you have a FPV system operating at 2.4G itself
3, 2.4G TX/RX link degrads in populated areas where you have lots of other 2.4G systems operating.

Well, all the above makes sense to me.

Point 1: Yes, higher the freq the more the attenuation from obstructions. Further, 2.4G is well absorbed by water particles in air, etc. That is the reason 2.4G is not used for submarine applications. Additionally, as an pratical example, you can hear lower feq radio startions over a long distance than the higher freq radio stations. (But here ionosphere reflection comes to effect.. anyway you get the idea)

Point 2: Its a matter of how much bandwidth does the FPV system occupy in the 2.4G spectrum. If it gobbles up a lot of the spectrum then the TX/RX system is left with a narrow band to operate. This would create conjestion in the link... lots of collision, errors might happen. Usually, if you need video or high speed data then you may be needing a larger bandwidth. If I were to do a FPV, I would use different freqs for the systems.

Point 3: Yes, there are many gadgets that operate in 2.4G - right from the gate openner till your wireless broadband... So, like Point 2, the available bandwidth of the 2.4G spectrum is very crowded. Obviously, your TX/RX system is gonna choke.

-Ismail

Here we go again... I am going to enjoy this!!


Could also be due to interference from the FPV transmitter which is sitting in the same airframe (read closeby) and may be connected to the same battery without filters. Much like near a HAM radio, a lot of other receivers can also tune into its BFO (beat frequency oscillator), if the transmitting antenna is powerful and special care is not taken to suppress unwanted splatter of nearby frequencies. In fact a normal radio receiver will pickup only the BFO if near enough (within 5ft) irrespective of the suppressors.

It would be quite revealing to understand the circuit diagram used for connection of the two systems and how they interact.


The answer to Sai's question of interference from other systems using 2.4 Ghz, quite possibly, is the fact that these systems may not be in line-of-sight with the RC rx. It would certainly crowd out the RC system if there were too many systems in line-of-sight of it.

Saju

As I understand from Ismail and Saju's reply :

1) Range for 2.4 G is largely line of site .
2) Obstructions can  lead to linkage breaks
3) Monsoon a humidity could lead to linkage drops
4) Any application that uses a large bandwidth could result in choking of the 2.4 G set up
5) Many 2.4 g appliances operating in proximity can result in choking as well.

So might not be a great idea to use 2.4 G for Boats , float planes , Video transmission from aircraft , cars in city etc.

As far the use of 2.4 G i have myself had an experience when we were testing a UAV system for a college here , the Auto Pilot ans Video down link were both on 2.4 G while the radio was on 72 Mhz . The  resultant clash of the autopilot and Video resulted in the Video getting disconnected time and again.

Like how we figured that heating of the receiver is a possible problem  the same way I wonder if there are any test made that check the  moisture content / humidity levels that affect  transmission.

Sai

Except for the clarification that line of sight is kinda important for 2.4 (which is an issue for FPV, not at all an issue for regular RC flying), everything else is discussed in the earlier threads.

Other 2.4 devices clobbering up the spectrum is an issue, the question is when does it become a practical problem ?  Not in routine use; unless you are flying right next to a 40 apartments building each with a wireless N router (or something like that).

The fact  it is an issue that might not be a problem for us in India today . This could present a problem to RC cars and heli flying around the house . Possibly even if park flying becomes popular in India like abroad .

I am just trying to understand the pitfalls in 2.4 G as I am getting into it .

So now it does not look as bullet proof as it was  made out to be earlier  the peace of mind and all that jazz . It seems as vulnerable as the good old faithful Mhz technology on analysis only  slightly better  the aim here is to discuss pro and cons and understand them  .

Sai

That "as vulnerable" part is where your understanding is totally wrong, or you refuse to take it in !

On 72, someone comes up on your channel, you are toast. No "if", no "but", not even "sorry".  That is what 2.4 solves.  Any other benefits (or even problems) with 2.4 are at best "collateral".

Do you see anything like "peace of mind" jazz now ?

I may be getting old, but I just cannot see how "significant crowding" of the spectrum, which is practically not an issue, can be "as vulnerable" as just ONE other guy messing with you, intentionally or unintentionally !  Now it is difficult to "quantify" what that "spectrum crowding" is, all we know is that about 40 transmitters (of the same type) working together did not do it, so it has to be significant !

Sai, don't worry, you can still sell your current stock of 72 stuff  ;D  But don't order much more, you know why  :P

In fact, you may be looking at museums to find non 2.4 stuff soon ;D ;D ;D

Oh yeah...  we are well on our way to hitting 4K posts before the midnight of August 4th, the deadline for the sweepstakes  8)

Anwar ,
It seems you are unaware that there are more people who trust the Mhz freq. still so selling Mhz Radios is not an issue at all.
Quite the contrary to what is going on here .Its only a few here , there is a far bigger world not represented here  ;D
The  forum's in India  represent only a hand full of aero modelers

So don't worry about my sales

In fact you will be surprised despite all this talk and hype about 2.4 G there are many using their Skysport 4 channels with V tail mixers to fly elevon planes .
Sai

Joking aside, I was really meaning to tell anyone who is getting a new radio to look into 2.4. 

I am sure 72Mhz will live for a long time, as there are multiple applications where that is the right choice.  But for routine usage, it is a world of 2.4 already (in fact, knowing what I know, I cannot even say that "it is going to be 2.4" as it has already arrived).

Anwar you are right I am also getting into 2.4 G as well but  knowing all the pitfalls helps me to better choose the route I will be taking in adopting this technology .
Eg
I now know thanks to the forum :
1) that the only 2.4 G branded system that has had the least problems is Airtronics .All others like Futaba, JR , Spektrum etc have had their major share of problems.
2) I know that Assan is a good route to take as their reliability and performance has been good and are a great value for money being low on future costs .
3) I know that Line of sight is a limitation for 2.4 G
4) I know that heat and moisture affect 2.4 G
5) Though practically rare but lock outs due to over crowding of band width is a  possibility
6) I also know that obstacles like trees etc can be a problem as well .

The purpose is achieved  {:)}

Sai

Airtronics should have a better name in the market than what they have now.  Their products are good in terms of design and build quality.

But they seem to be lacking in marketing, and even more importantly, they are bit late in terms of some features and some aspects of usability (a bigger LCD screen, for example).

Airtronics and Hitec have been late to the game but take a look at the feature set of their new radios SD 10G and Aurora 9. They are a generation ahead. It is JR and Futaba that has to play the catch up game now.

What are some of the things that you noticed that are unique in these new radios ? 

That would be really good information for everyone else here.

Dear Sir,
This may also be due to the the fact that radio systems like Futaba, JR , Spektrum etc are used far more widely worldwide than Sanwa Airtronics which is seen around only of late................ therefore maybe due to their widescale usage, their issues get discussed more often unlike the less used brands................ probability perhaps ???
Edwin

You mean like people saying "Apple Mac computers are not affected by viruses". Wait till Macs are common with everyone !

But with Airtronics, I think that case is different.  This is mainly confirmed by people who try to "break" radios by doing all sorts of tests.  They have been able to find issues with other brands, but so far have failed to find major problems with Airtronics (at least based on what is available on the web).

Much wider usage may bring out yet unencountered issues with Airtronics, we only know what we know so far.

Sanwa/Airtronics was quite poular in Europe and UK before Futaba marketing blitz.

Again, I am not sure that is a practical issue.  You know how you can get a 2.4 wireless network connection in the next room even if it is behind a wall; so in open spaces with just a few obstacles at a distance, this should be one of the last concerns.

Anwar ,
There is no need to get defensive about 2.4 as a technology , we all agree from the trends that it is the future of radio's more so in my case as I am a seller  who believes in keeping up with technology  . I prefer educating  and informing buyers about what they are getting into

I am not  on  a 2.4 G fault finding mission because I am one of the few who sell Mhz Radio's  , I am trying to  get people to understand it better  so that it can be adopted to the benefit of all as there are more options other than the branded ones with the same 2.4 G .
The attempt here is to basically list issues that could arise with the usage  so that users including myself will take precautions knowing fully well the problems that can arise and possibly anticipate them when and if they do.

Like how in the case of the Mhz transmitters we know to do a frequency check prior to switching on and when we have a glitch in the air we know that it could be due to temporary interference  the idea here is to list such issues so that  users know what can affect them and what to avoid/ look out for even in the rare case apart from receiver heating , voltage etc which are within their control.


sai

Again, you seem to be missing the point. I am anything but defensive, "I" am irrelevant.  Only the subject matter is relevant.

I am highlighting what the practical issues are.  Not remote/impractical possibilities.  The only thing I care about is to "let people worry about things that they REALLY NEED to worry about".

In case you didn't notice, I questioned ONE of the SIX things you listed; because it was literally begging to be questioned ! Especially for beginners, a list of 5 is better than a list of 6, so that they may make the right choice for these times....

I have listed the features that I found attractive for this class of radio.

Airtronics SD10G

Firmware Updates Available On-line With Use of Airtronics USB Cable and Program (available separately). I can confidently buy because even if there are any issues found they can be fixed by updating firmware ourselves. Hopefully any lacking features will also get added.

Rx works down to 2.8V.

100% Completely Assignable Switches

All Switches Are 3 Position Switches

Model match feature available

Unique “Direct Model Select” Allows Selection of 3 Favored Models Without Entering the menus.

3-axis Triple Rates And Triple Expo With Unique Adjustment in Each Direction of Travel

Easy Navigation, Spreadsheet-Like Menu For Control Surface/Swash Adjustments. This is based on airtronics team pilots reports, not my evaluation.

Ball Race Supported Gimbals With Adjustable Springs And Adjustable Throttle Ratchet

Cross Trims

Failsafe Programming Available On All Channels

Transmitter Is Compatible With Lithium 2 Cell Batteries

Latency numbers are supposed to be the best in class.

-ves
I don't really dig the looks of this tx.
Limited vendors. But tower is one.
Model match available only with 10ch rx.

Hitec Aurora

Telemetry

Fully Assignable Control Switch, Knob, Stick and Digital Trims

5.1 Inch Wide Backlit Touch Screen. Customizable Menus.

Highly Sensitive 8 Ball-Bearing Gimbals with Adjustable Tension

-ves
external wire to antenna
limited vendors

Many of these are supported by other brands, on the higher end radios. But having them together in one radio at the 10channel level is good ( as in the Airtronics one).  Also, there is a way to store models online (outside the radio).

One negative about Airtronics is that the trainer works only with the same model, not earlier models.

SANWA/AIRTRONIC as a radio company is in the market for more than

Also they have won more world championship both cars & air put together than any other radio manufacturer.

As a company its nearly a half century old and has been sell radio for more than 4 decades.

This just a small information so people are well aware of the brand.

Sanwa started to sell under the Airtronics brand from 1982 in the US.

Airtronics are working on the same is what i have been informed.

I knew some smart ass will say this.  8-)  ;) That is why I wrote "I have listed the features that I found attractive for this class of radio."  You don't usually see these in a sub $500 radio.

The mixing is supposed to be very flexible too unlike most radios. I don't have full details so I had left that out.

And I forgot one. All 10 channels are fully proportional. Unlike........................Futaba

Another basic question :

Is there  any appreciable difference in speed between 2.4 g and Mhz . I mean the time lag for the servos to react in air to a command from the Tx.

I know Anwar will be happy with this question thought I will do him a good deed early in the morning  ;) ;D ;D

Futaba claims that the lag in their Ghz is half the lag in Mhz. Ghz is short waves and hence travel fast (they claim) However, the lag is so negligible that for a normal person, it is not very evident and cannot be measured as an indication of significant difference.

But technically speaking, yes. Ghz is faster than conventional Mhz

Amen to that !  This whole lag thing is kind of difficult to even notice for 98% of the fliers.  Unless you are doing things like "crack" movements in heli flying, you will hardly notice anything.

But people do talk a little about this thing called a "connected feeling" while flying.  That is significantly influenced by the "resolution" of the connection (for example, 1024PCM versus 2048 PCM).  And you need really good digital servos.

And there are many other issues also, that plays into this "lag" thing.  For example, the Futaba 9C radios (which was like the choice radio for a large percentage of users, until recently), is sort of "known" (not sure by who) for its "lag" in CCPM mixing.  I flew one for over a year, and never felt a thing.  Only when I switched to a more recent radio, I felt a little something, even that is again so minor a difference for my current level of flying.

In short, this whole "lag" thing is probably not worth discussing.

GHz does not travel faster than MHz. I guess we have all long forgotten school physics.

GHz transmitters use a higher bandwidth than 72MHz (3-5kHz BW). So they are able to send information in a much shorter duration. That is why the servos react faster. Whether the difference is perceivable is another matter. This is similar to you downloading through a dial up connection vs broadband. You have higher bandwidth in broadband, so you get the file sooner.