Serious 2.4Ghz Problem arising.

[flytilbroke]

A thread has highlighted a problem. This has been discussed before and has been foreseen may happen.

 

The thread is on the LMA Forum and states that illegal Transmission power from Illegal First Person View units fitted to Rc Aircraft have been proven to have caused other Models to crash.

 

The units are transmitting in excess of the legal UK limit by up to emiting up to 1000mW when the allowed limit is 100mW. When an FPV model fitted with these Illegal modules approaches one of the legal 2.4Mhz the 100mW 2.4Mhz Rx gets swamped.

 

Some advise has been promoted by individuals that a Frequency Monitor unit is availlable which can detect the illegal FPV units before they perhaps cause legal 2.4Ghz users any serious incident.

 

 

[Martin Harris - Moderator]

This is the scenario that's worried me with non-hopping systems.

 

I wonder which systems the affected models were using? Is this swamping occuring over the whole 2.4GHz spectrum or does it only affect (as I think may be the case) a number of adjacent channels?

[Chris Johnson 1]

The legal limit for video transmitting on 2.4 Ghz is in fact only 10mW and 25mW when using 5.8Ghz. (both legal FPV frequencies)

If sensible frequency controls are used at clubs, which has alway been the case, then no one should be affected.

[Tom Wright 2]

How many FPV units are there in the UK ?

 

Surely they must be illegally imported if emitting more than 100 mw ?

Edited By tom wright 2 on 25/02/2011 23:15:54

Edited By tom wright 2 on 25/02/2011 23:23:05

[Martin Harris - Moderator]

Chris said, "If sensible frequency controls are used at clubs, which has alway been the case, then no one should be affected."

 

 

Trouble is, from what I've read, the rogue model wasn't being operated from the club where the models were affected. With the range of an illegal power link it could be being operated from anywhere within a mile and a half (or maybe more?) radius of the legitimate operation.

Edited By Martin Harris on 25/02/2011 23:16:22

[Steve W-O]

I don't know the story, or the make of equipment being used, but there are two possibilities.

 

If the offending signal was close by the affected equipment, it could affect every channel on a full hopping system. This would occur because the receiver somewhere in the circuitry has an automatic level control, which will effectively turn the volume down on incoming signals, so the weaker signal would not be heard. This is not quite as aggressive on digital equipment as it is on analogue, but it still happens, as overloading of the decoding circuitry has to be avoided.

 

 

But the offending transmitter and affected equipment would have to be close together, because at a couple of hundred feet, to double the received signal from a 100mW transmitter, it would have to put out 10W

 

 

The other possibility is one I was trying the other week. I have some cheap 2.4 gear that operates on two channels, it doesn't hop. If I force that (by putting it right next to laptops and wireless routers which I have manually selected channels) to operate on two channels next to each other, then turn on a router which is on one of those channels, the servos either become slow to respond and jerky, or control is lost.

 

This is made much worse if I turn on another of the same "two channel" 2.4 transmitters next to the one under test.

 

 

On a full hopping system, there are still some pauses in servo movement, but control is not lost.

 

 

This is not usually going to occur in real life, as the receiver was inches from the wifi antennas, and 25ft through a wall to the transmitter, which meant the signal from the transmitter was more than 50dB down from what it would have been if it was also right next to the receiver.

 

I also noticed that if one of these transmitters was within about 8' of the router used for broadband, it killed the link, and no one in the house had internet !

 

 

What this means to me is that it is possible, but unlikely.

 

My "experiments" were unrelated, I just wanted to see if it was possible to interfere with a 2.4gHz signal, it is, but not in a way likely to be found at the field.

 

 

Monitoring equipment would be OK if you knew there was a problem, but if the interference was not always present, control would be lost as it is seen on the monitor, by which time it is too late.

 

And as 2.4 is line of sight, the model may see the interfering signal while the monitor does not.

 

While it is easy to prove that a signal can be interfered with, the conditions that need to be met for it to do so are unlikely to be present on a flying field.

 

If when this happened, the offending model was some distance away as suggested, I would be looking at the quality of the control equipment as well.

 

 

I didn't see any links, so I don't know what actually happened, or how the cause of the crashes was proved, and how impartial that proof was.

 

 

 

[Steve W-O]

I found the discussions, and the one on the forum where a member of the club concerned started the thread is full of doubtful comments, some of them questioned by other posters.

 

Then he says "knowing who is causing it is one thing, proving it is another"

 

Then on the LMA forum, a member of the club concerned says "We fly next to a housing estate and one of our thoughts is that someoen might be doing this deliberately."

 

So there is another possibility.

 

It seems that nearly all of the equipment affected was DSM.

 

 

To be honest, although it is something that needs to be considered, I think a lot more solid fact is needed before anyone worries a great deal, or chuck all their DSM equipment in the bin.

[GONZO]

It's very easy to buy a 2000mW amp for your home router from the 'Bay'(£40'ish) so that joe public can opperate their lap top in the shed/office/workshop at the bottom of the garden. I doubt that joe public knows or cares if this is legal/acceptable. 2.4 is a catch all general use band and the equipment using it has to accept interference from other users as part of the 'no licence no fee' use of the band. The problems with RC in/near an urban location will only get worse IMHO as more and more use is made of the band and the noise floor rises. 35 is the only band exclusively reserved for RC planes - use it or loose it!

FPV 2.4 is an analog transmission on one of upto 8 channels HERE

[Alan Cantwell]

isnt 35 a military frequency? and we just have a bit of it? and this FPV thing, just how much range do the trannies have? would they not be in danger of getting giddy, and FPVing out of range? BMFA guidlines state that the FPVer should be on buddy box, and the box holder should have the model in view, dont they?

[Biggles' Elder Brother - Moderator]

They do indeed Alan, as do the equivalent guidelines in the States and most other countries. If I understand it correctly this was a position that the BMFA thrashed out with the CAA.

 

But I've been thinking for sometime that something very odd is happening with FPV. Its only my impression, but I think most of the FPV activity is taking place by non-BMFA flyers.

 

FPV seems to have short-circuited the "usual" route. You might think, given how technically complex it is, that it might represent some kind of pinacle of RC flying, a bit like "large models" or "gas turbines". Something RC flyers graduate to should they wish to. But I don't think that is actually the case. I think a lot of FPV flyers are "direct entry" - that is they have no, or little, previous RC flying background. For me this tends to be borne out by the fact that very few FPV fliers post on here - we hardly have a thriving FPV community amoung "standard" modellers. Indeed it sometimes seems to me that, novelty value aside, mainstream RC modellers like most of us don't actually seem to be that interested in FPV.

 

All of this means I think that many FPVers are operating completely outside the system - such as it is. Add to this the fact that the nature of FPV tends to lead to "lone flying" in isolated places and you can see that the BMFA can say what it likes - but it isn't necessarily speaking to the actual practicioners! My suspicion is that many FPV fliers aren't even aware of transmission power limits, frequency protocols or any such details. They may not even be fully aware of us! They haven't come from the modelling background.

 

Just to finish - I want to stress I've absolutely nothing against FPVers - good luck to them. And I am sure that there are flyers who do FPV who have a long pedigree in mainstream RC flying. All I'm stating are my impressions that this isn't the norm - ie that it is almost something separate from the mainstream of RC flying and that perhaps that is an undesirable thing leading to potential problem like this.

 

BEB

[Steve W-O]

BEB, I don't know if I can see any reasoning to think that.

 

The person who was blamed (not yet proven, and now they suspect it could have been another cause) has a web site. He must be in contact with other interested people, or hear from them in some way otherwise the site would serve no purpose for him.

 

Nobody who has been in he UK for more than a short time would not know that just about everything is regulated, with the possible exception of air we breathe. They may not know the regulations, but someone with internet access and average intelligence would come to be aware of some of them.

 

 

Being outside the BMFA yes, but from a posting the other day, that was more the fault of the BMFA, as they weren't supportive, so the FPV people have formed their own association with their own insurance scheme. The posting the other day commented on how cheap the insurance was.

 

I would guess that they are fairly competent modellers, probably don't frequent the normal RC forums simply because of the frosty reception they get.

 

 

Everybody's talking like the person who was blamed was the cause, but lots of the comments don't add up technically, and one of their club members posted that they had thoughts it could of been intentional interference from the adjacent housing estate. Could also have been unintentional interference from the housing estate.

 

If the problems stop now the person blamed has changed his video frequency, it means nothing, as if it had been some one in the estate intentionally interfering, no doubt they are following it on the web, know the other person has changed frequency, and what better way to reinforce his blame and get away with it themselves than by choosing that time to stop.

 

 

 

Not enough facts, and too may assumptions!

[Tom Wright 2]

Surly the principal point with regard to FPVF is the r/f power output of such equipment .

As it operates on 2.4GHz it is subject to the same RT act and enforced by OFFCOM in the same way that all our conventional R/C equipment is.

Are we saying that none compliant FPVF equipment is sold in the UK or imported by individuals who may be ignorant of the regulations?

 

TW2.

[Steve W-O]

Posted by tom wright 2 on 26/02/2011 13:11:06:

Surly the principal point with regard to FPVF is the r/f power output of such equipment .

As it operates on 2.4GHz it is subject to the same RT act and enforced by OFFCOM in the same way that all our conventional R/C equipment is.

Are we saying that none compliant FPVF equipment is sold in the UK or imported by individuals who may be ignorant of the regulations?

 

TW2.

 

 

It is easily available, sold for various uses, by sellers in the UK and abroad.

 

The power is probably the point that more often makes it illegal, but the power of most of them should not be an issue in itself to good RC gear.

 

If you have a field 1000 feet across, with a model in the middle, a 10W (10 000 mW) video transmitter on one side of the field, and the models transmitter on the opposite side of the field, then all other things being equal, the signal from the video transmitter would only be twice as strong as the transmitters signal. If that was all there was to it, only the power, that would not be a problem.

 

It would take other additional factors to cause a problem.

[GONZO]

Other FPV video frequencies available - 900mHz, 1.2/1.3mHz and 5.8gHz. First two not legal, but whos checking frequencies and o/p power. I suspect its like most law enforcment - don't cause any major(financial) problems then no one whants to know.

On the question of RC for FPV - some use 35mHz with longer Rx aerials for increased range. Others use 430-440mHz UHF frequency agile spread spectrum sets.

[Chris Johnson 1]

Hi again.

If anyone is interested the website mention above is most likely www.fpvuk.org

Yes we do have our own insurance and rules. We DO NOT in anyway condone anyone exceeding the legal Video transmitter power. Also stated above is that the gear must be imported. That is not necessarily the case, remember when the Police radar detectors were all the rage? they were not illegal to sell or buy but when you turned it on it was totally illegal. Now most SatNavs have all the speed traps programmed into them so what was the big deal. CB radio was another big hoo hah over nothing.

I have been flying RC for 40+ years so I am not a newcomer. I consider myself responsible and as such I am a member of both FPVUK and BMFA. I fly at a BMFA site with the blessing of the other members and as a sensible precaution we operate a frequency control system. I fly 2.4Ghz in my non FPV models and 35Mhz with 2.4Ghz Vtx for my FPV ships.

The last time I was flying I was FPVing and chasing a non FPV plane and he never got a single glitch. Go Figure.

As always when a "new"thing comes out there is the usual paranoid groupies.

Read up and learn is my policy before I comment.

[GONZO]

On the subject of 2.4gHz RC - there is this increased o/p system readily available made by This company and sold HERE . It's cheaper than the official bits and has 1000mW o/p - not that I've heard of anyone using it in this country.

2.4gHz is used for FPV video because it has the most modern cct design and does not suffer from the signal path problems of 5.8gHz.

[Martin Harris - Moderator]

Chris,

 

What concerns me as a conventional flier is this sort of statement:

 

+27dBm typical output power :

The rated output in real world terms. Dbm can be used to calculate range capabilities of each component. From the figure +27dbm we can determine this is a 500mw transmitter.
Mw is another term used to state the power of the transmitter. To be legal on the 2.4 Ghz band in the Uk the maximum permitted power of the transmitter is 10mw.

 

 

Although it clearly states the legal position, is this typical of the equipment used in the UK? What power output video transmitters are popular with your law abiding members?

[Tom Wright 2]

So if a 5w TX was 500ft away from a 100MW TX the Rx would see an equal signal from both TX assuming both TX were on the same channel.

High power outputs also raises the question,...Is it likely that a commercially available TX would have a battery capable of delivering say 10w which is 1a current draw from say a 10v battery? this would only give around 30 min transmission time from a typical 700ma TX pack.

My first take on the original post would tend to be a bit sceptical,i wonder what the account of proof reads like has anyone got a copy?

TW2.

[Doug Ireland]

Hi Martin, I wasn't about the 10mW max output you quoted as the limit for 2.4GHz in the UK. I've just looked at the "ofcom" website and they say the limit is 100mW. I hope so 'cos that's what my DSX9 puts out and I bought it from Webbies!

[Steve W-O]

Posted by Doug Ireland on 26/02/2011 14:26:33:

Hi Martin, I wasn't about the 10mW max output you quoted as the limit for 2.4GHz in the UK. I've just looked at the "ofcom" website and they say the limit is 100mW. I hope so 'cos that's what my DSX9 puts out and I bought it from Webbies!

 

 

I think it was the video signal referred to.

 

RC transmit power is 100mW as you say

[Steve W-O]

Posted by tom wright 2 on 26/02/2011 14:24:41:

So if a 5w TX was 500ft away from a 100MW TX the Rx would see an equal signal from both TX assuming both TX were on the same channel.

High power outputs also raises the question,...Is it likely that a commercially available TX would have a battery capable of delivering say 10w which is 1a current draw from say a 10v battery? this would only give around 30 min transmission time from a typical 700ma TX pack.

My first take on the original post would tend to be a bit sceptical,i wonder what the account of proof reads like has anyone got a copy?

TW2.

 

 

 

I used the 10W only as an illustration, as it is double the signal at the receiver of 100mW at the same distance.

 

The previous examples suggested a power of 1W from the video transmitter, which will give a slightly lower signal at the receiver than 10W.

 

 

As for proof, they said they had no proof!

[Tom Wright 2]

Based on the information so far it occurs to me that a conventionally equipped model would have to get very close to an illegal TX , before it became a problem,talk of 5w or even 10w transmissions ,smacks more of malicious intent,rather than accidental interference.

Steve i posted this before i saw your previous post sorry.

TW2.

 

Edited By tom wright 2 on 26/02/2011 14:45:17

[Tom Wright 2]

Steve my comment re proof was based on the second para in the first post.

TW2

[scott cuppello]

We discovered this at out club around 3 years back, and banned any 2.4ghz camera then, and that was a unit [of mine, I was flying on 35mgz] putting out a mere 10mw. If you look at the FPV scene, it's all going 5.8ghz, so it's not something I would worry about too much, when we tested, basically, you had to have the 2.4ghz camera witinh 3-4ft of a reciever to block any form of signal, and that was only effective in "range test" mode, but for safety sake, we took the obvious precaution.

 

Bottom line is that there is more iffy 2.4hgz equipment being used out there than you really want to know about, take your pick basically! It's still the safest flying frequency yet.

Edited By Scott Cuppello on 26/02/2011 14:46:02

[Steve W-O]

Posted by tom wright 2 on 26/02/2011 14:40:42:

Steve my comment re proof was based on the second para in the first post.

TW2

 

 

The only thread I could see on that forum was the one by a member from the club affected, so I certainly did not see any proof.