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WiFi Interfering with 2.4GHz radios??? Urgent issue!

BigHarv

Heliman

West Linn, OR - USA

I've always thought that our DSM or FASST systems were impervious to WiFi and cell phones but now I'm thinking that may be incorrect. I hope some of the gurus on this forum, particularly guys from Spektrum or Futaba, will chime in on this.

Our club put on a great FunFly this last weekend at a private grass airstrip. The flight line extended along the entire runway which I would estimate is at least 1500ft long, probably closer to 2000ft. With about 100 pilots, flying was happening along the entire flight line.

As a courtesy to fellow flyers and a contribution to the festivities, I equipped my motorhome with a 3G industrial grade broadband router (a Zyxel 2WG) and a high-gain 3G antenna. The router was configured to share the broadband with any WiFi-equipped flyers via 802.11b. I even purchased two relatively expensive 18db WiFi antennas so that folks within 750 feet of my motorhome would be able to get on-line to check e-mail, etc.

I got there on Thursday afternoon and by Friday afternoon, 5 pilots reported transmitter/receiver brownouts (causing some serious crashes) all at exactly the same spot on the field. No one reported any such problems anywhere else on the field. That spot was directly on a perpendicular line from motor home about 200 feet out. The pilots having problems were using both Spektrum and Futaba gear.

When I finally heard about the problems I shut my system down and there were no similar problems from then on. I can't help but think that my system was the cause. I'm not sure if it was the 3G signal or the 802.11b signal, but it's hard to imagine that this was a coincidence. Naturally, I felt terrible and it pretty much ruined the rest of the 4-day funfly for me. I'm even covering some of the cost of one of the crashes. I wish I could afford to make everyone whole, but I can't.

Does anyone have any authoritative information about the use of 3G or WiFi in the vicinity of our DSM or FASST radios?

Assuming I'm not wrong in taking the blame for the problems, this is something that everyone should be aware of. I know that most folks, myself included, generally have no problems flying in WiFi or 3G range. Maybe it was the extra power of the antennas or just how much flying was going on (increasing the likelihood of a rarely occurring problem) that was the root of the problem. But I would sure like to get to the bottom of this so that no one else has to suffer similar consequences.

Any help or enlightened opinions would be appreciated.

Thanks.


BigHarv
TRex 450, Raptor 50 V2, Rap 50 Titan, Rap E550, Rap 90SE, Trex 600NPro, Trex 550E

06-22-2010 02:12 AM
Bundian

Veteran

Fort Lauderdale, FL USA

Actually in theory the Spektrum and FASST are not possible to get interference but that's to a certain level of course.
For example if you're using a 2.4Ghz FPV gear with a 2.4 radio after a while you will get interference because your transmitter is getting farther away from the aircraft while in this case increasing the power of the video transmitter which sits inches away from the receiver, chance of interference gettin bigger and bigger the farther you fly your aircraft.

Now your blastin away with a very powerful antenna from your RV and adding 2 18db antennas to it those signals are in theory can be picked up miles away, the radios we use just can't compete with that kind of power.

I hope it makes sense, i know these radios are advertised as impossible to get interference but the power you have on your RV in this case acts as a jamming device

Fly it like you stole it!!!

06-22-2010 02:52 AM
Fastsrt

Veteran

Lebanon, Tn

Sorry for the bad luck, I hate to hear that happen but me and a friend have talked about this issue quite a few times. With wifi being 2.4 and starting to be installed everywhere that you can think of and with spektrum, futaba, jr and the others also being on 2.4, yes there is going to start being some interference issues arising.
With as many wifi hotspots that are in place nowadays, if anyone flies at a field that is relatively close to it i bet they will have the same problem happen but maybe not every trip out.

06-22-2010 03:09 AM
Aaron29

Elite Veteran

USA

i know these radios are advertised as impossible to get interference but the power you have on your RV in this case acts as a jamming device
So true, think of it like trying to give light signals to a ship using a flashlight, and then a lighthouse starts beaming light at the ship.

06-22-2010 03:11 AM
Aaron29

Elite Veteran

USA

With wifi being 2.4 and starting to be installed everywhere that you can think of
Yup. Those old codgers on 72Mhz using PCM might have a point...at least we have some CLAIM to 72Mhz. The FCC set it aside for us. They did no such thing with 2.4. We cannot cry foul when jammed on 2.4Ghz because it is universally used.

Please all, keep this in mind when discussions start to arise to get rid of 72MHz because we "don't need it anymore."

We just may find that as things get noisy out there that we need to retreat to 72Mhz after all after a nice college try at this.

06-22-2010 03:13 AM
aceisback

Senior Heliman

Terre Haute, IN

I think it might be safe to consider that it "MAY" have contributed to the crashes, but I wouldn't accept blame or responsibility unless it could be proven. It is a common problem that everyone blames their crashes on radio brownouts, lockouts, failsafe enaged, radio hit etc. The more sophisticate our electronics become, the more people won't admit they dumb thumbed it. Nobody crashes anymore, they have radio problems.

06-22-2010 04:29 AM
ShuRugal

Key Veteran

Monterey, CA

Nobody crashes anymore, they have radio problems.
Yeah, happened to me this weekend at the field flying a cheap foamie. It passed over the brim of my hat in a high-bank turn, and in that split second i couldn't see it, my radio got jammed up and it belly-flopped right in front of me at full throttle! i swear, it was interference from my 2.4GHz hat!

;p

AMA 700159
Fomer Ignoree

06-22-2010 04:39 AM
rexxigpilot

Elite Veteran

Florida

I don't believe for one second you had anything to do with it! As for the person making you pay for his crash, he is either scamming you big time or just doesn't want to admit he dumb thumbed it. In any case, it is not realistic to think you caused the crashes.

All 2.4GHz systems are required to be tolerant of other users on the frequency. The design of our RC systems, like almost all 2.4 devices, use a specific codec to allow one transmitter and one receiver to communicate. Although the RX in the heli may hear your IEEE 802.11b, 2.4 GHz signal, it will be rejected as something other than the signal it is listening for.

The 3G signal is the US is between 850 and 2100 MHz, so it couldn't interfer with 2.4 GHz even with the proper codec.

Think of it like listening to music. Now listen for a specific instrument. Can you not pick out each instrument indivudually? Sure you can. Cheer up. It was not your fault.

06-22-2010 04:59 AM
rexxigpilot

Elite Veteran

Florida

Here's another analogy for why your 2.4 WiFi system didn't shoot down the helis. My son recently went to Japan but speaks limited Japanese. While in a shop in Tokyo he overheard a conversation from across a noisy room. There were many other people speaking loudly close by. Yet, he was able to distinctly hear every word of the distant conversation. Why? Because they were speaking in English, my son's native tongue! All the Japanese conversations faded into the background. Language is a codec.

06-22-2010 05:12 AM
Kenny Johnson

Senior Heliman

12mile S/E of AMA Headquarters. IN-USA

Here's another analogy for why your 2.4 WiFi system didn't shoot down the helis. My son recently went to Japan but speaks limited Japanese. While in a shop in Tokyo he overheard a conversation from across a noisy room. There were many other people speaking loudly close by. Yet, he was able to distinctly hear every word of the distant conversation. Why? Because they were speaking in English, my son's native tongue! All the Japanese conversations faded into the background. Language is a codec.
I sorta disagree.
What if the Japanese people were yelling? would he be able to hear the English then? Hmmm, depends I guess how loud they were yelling.

Example, if the gentleman's wifi setup was say tx'ing 4 watts of power compared to 1 watt of the output of the RC tx, could it be to much noise and the reciever and not be able to understand the codec.

I have no clue to what the actual tx EIRP "Effective isotropically radiated power" that our transmitters produce, but did read that he was using very Hi-Gain antennas. I would bet that he was transmitting way over FCC EIRP specs.

I wouldn't rule this out.

Team Rotor Rage

06-22-2010 05:56 AM
Aaron29

Elite Veteran

USA

All 2.4GHz systems are required to be tolerant of other users on the frequency.
Yes, but if a system is not playing fair due to malfunction, out-of-spec manufacture, or poor design, you can be jammed.

2.4GHz is not magic and will not defy the physical laws of our universe. If the signal to noise ratio becomes too low due to a barrage of noise on the 2.4Ghz frequency, you will get a nice lockout.

Plain and simple. The benefit of 2.4Ghz is that the receiver binds to a certain transmitter and discriminates based on that. It does not mean that the system is invulnerable to noise jamming. An example of what 2.4Ghz does is if I signal you using a flashlight, I do it using certain colors and rates of flash. You know the colors and flashes ahead of time and can discriminate my signal from other flashlights signalling their respective receivers.

Other flashlights signal their respective receivers using a different color and different flash, so no one gets mixed up.

This is how 2.4Ghz works, it discriminates. It is not however, immune to noise jamming. No EM technology is.

Noise jamming would be like a bunch of guys using flashlights to signal their resepctive receivers and then I pull up with a Jeep with a full row of gigantic lights and blind the crap out of everyone. Doesn't matter what the flashlights are doing then does it? Because no one will be able to see it even if they are looking at it. The noise (Jeep lights) will overbear the signal (flashlights flashing coded information).

Plain and simple, you can speak English all you want amongst Japanese folks, but take this same scenario to a rock concert and stand 15 feet away from your chatmate and you will hear nothing. Your friend who picked out the English conversation across the room full of Japanese banter probably had a signal to noise ratio that was just above the threshhold and thus could still pick out the information.

The signal to noise ratio, once it drops below the threshhold, denies any information. Systems that are designed correctly should not create enough noise to do this. They are either limited in output wattage or bandwidth. But if broken...

I, too, would do some tests. Of course it could be VERY difficult to isolate the problem as the beams of EM may not be where you are testing. You just can't tell where the antenna pattern is creating the noise. You may think all is well because you are testing in a noise free area. (Like flying behind the jeep in my example.) But then if you move to the wrong piece of sky you get noise. Finding that piece of sky might not be straight forward.

I would assume no responsibility if I were you, but some research is a good thing here. We might all learn something.

06-22-2010 06:14 AM
aceisback

Senior Heliman

Terre Haute, IN

Could be that after the 5 crashes, everyone else quit showing off, therefore no more crashes. The more helis/planes present at a funfly, the more crashes.

Seriously though, don't assume blame unless you can recreate the scenario. Try putting the rx's in an RC car and fire up your equipment and drive the car around to see if there is any interference. I know ground is going to be different than in the air, but it might yield a clue.

The field we fly at has a wi-fi set up in the hobby shop Receives wireless internet from a local tower and then transmits to the owners house and we have had no issues and we are only a few feet from the antenna. Not as powerful a setup as yours, but I know there is no interference from it.

06-22-2010 06:17 AM
VooDooX

Elite Veteran

San Francisco Bay Area CA, US (San Mateo)

he talks about interference and has a spectrum graph up and everything so it is possible yours could have drown out some systems but unlikely

Watch at YouTube

Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001

06-22-2010 07:08 AM
marked23

Key Veteran

Lynnwood, WA

I was one of the pilots at Brooks that experienced a first-time-ever 2.4ghz interference of some sort. My crash was very mild, just blades, flybar and various links, so far.

I've never experienced any lack of confidence in my 2.4ghz equipment before. So I suspected that there must be some other explanation. I'm still going through my equipment to make sure it wasn't a frayed wire or something.

I'd be interested to re-create the circumstances and see if I can cause interference on the bench. I think I'm going to buy this Wi-Spy 2.4i and review the radio-noise before I turn on at a busy funfly.

BigHarv, I was at the very end of the field.. the South end. I was standing pretty close to my heli at the time. I encountered interference on one flight on Friday and had that crash on Saturday. Does that match with what you know about the other episodes?

-Mark

06-22-2010 07:12 AM
jgunpilot

Key Veteran

Pollock, LA

Did the people who took money for their crashes offer to pay you money to use your expensive wifi system, or was it more of a one way deal? I think I already know the answer.

06-22-2010 08:21 AM
davebNZ

Senior Heliman

Wellington, New Zealand

Worth a read ....

This article is well worth taking a moment to read. The guy is scientific in his approach and knowledgeable.

http://www.rcmodelreviews.com/fhss_vs_dsss.shtml

Then scroll down this, a lot of articles about brand specific problems.


Then have a read of this thread:

http://rc.runryder.com/helicopter/t586748p1/

All part of the understanding and enlighten of what is going on.

06-22-2010 01:11 PM
GMPheli

Elite Veteran

W. Bridgewater, MA USA

I have always wondered why 2.4 transmitters have such a small amount of output power compared to 72 meg. Most that I have seen are around 100 milliwatts. Yet 72 meg transmitters are around 600 milliwatts. Is 2.4 more efficient or something? It is kinda scary.

06-22-2010 01:13 PM
mlevings

Senior Heliman

Claremore, OK

For you guys wanting to use the wispy spectrum analyzer, here is a much cheaper alternative. http://www.streakwave.com/Itemdesc....irview2&eq=&Tp=
These work great. I use them regularly for troubleshooting wifi networks, but never thought to use one at the field before flying.

06-22-2010 04:02 PM
Gyronut

rrProfessor

Martinsville In.

WoW, great thread..............

We have alot of knowledgeable people here............

Rick

06-22-2010 04:52 PM
marked23

Key Veteran

Lynnwood, WA

mlevings... Good find. I ordered one. Their shipping charges ($15) are a bit high. It doesn't indicate what kind of software it comes with. If I can hook into the driver easily enough, I might write my own software.

06-22-2010 04:52 PM
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