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Bluetooth interference?


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Hello, 

After a couple of flights where I seemed to suffer a bit of interference, I wondered if the number of mobile devices in various pockets might be affecting things. Bluetooth, I believe, works on 2.4Ghz, and although range is limited, ones own pocket or even car is usually quite near the tx! 

 

Possible? 

 

Obvious solution is to leave BT off when flying, but still. 

 

Ditto data transmission and satellite guidance for agricultural vehicles? Not BT obviously but a potential cause of issues? 

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Generally we do leave the phones in the car, but with the number of devices using BT, I was just wondering. I hadn't read the Manny's Musing bit, I'll dig it out. 

 

With the frequency getting more and more congested, maybe its time to go back to 35 ?

 

 

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It would need someone on here who is really clued up on rf data protocols to give an informed opinion on this. I believe, as said, Bluetooth uses a 2.4Ghz band, but probably a totally different protocol to our sets. I think the latest FrSky txs use Bluetooth for the wireless trainer link, which suggests it doesn't cause issues with the model rf link?

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FWIW, the incident which prompted Manny's article concerned a transmitter apparently changing modulation methods in mid flight. Coincidentally or not, the pilot's phone (in his pocket) received a text message just before the model went out of control. I'm all for taking precautions, but I think it's important to be clear that, in this case at least, the issue seems to have been the electromagnetic susceptibility of the transmitter's digital circuitry rather than interference with its 2.4Ghz transmission.

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2.4ghz was adopted by the military to operate in crowded environments, and may frequency hop or other to maintain a signal.

Just look at the flightline at a model show with 10 and 20 pilots in the air at one time, and countless hundreds of onlookers with phones in their pockets, just feet away.

The airwaves are more crowded then ever, but 2.4ghz does its magic operating sucessfully.

We give it the best chance we can, by charging battery packs, having a frequent voltage check routine, and fitting and aligning aerials and antenna as best we can.

Drop outs and fades will occur, but the equipment 're-acquires in milliseconds. 

Installation and adequate power are key.

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On a some what related issue, my Nissan has forward radar  for emergency braking, at a T junction 100 metres from my house it 9times out of ten must pick up a signal and goes out of service. If I want it back I must stop and switch off to reboot, which is a bit annoying. Is this Bluetooth related does anyone know?

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  • 2 weeks later...

All of the advanced 2.4 GHz systems (Bluetooth, Zigbee, Spread Spectrum, etc) are designed to be almost totally immune to interference. Yes, ultimately you will reach a point where the signal is totally overwhelmed and control is lost, but until you get very close to that point, you will be totally unaware. The rate of data transmission is so high on modern RC systems, that even if half the "packets" are lost, you are unlikely to notice any difference.

 

The much more likely scenario is the RF bursts from a mobile phone breaking directly into the transmitter circuits. I'm sure you've all heard interference from a mobile phone on a HiFi system, or transistor radio, or even a wired intercom when a phone is close. A mobile phone can send out quite powerful, short duration bursts of RF that will break directly into poorly screened electronics. Most modern RC is pretty thoroughly screened anyway, as to meet CE and FCC standards, they are not permitted to radiate spurious signals from their own internal electronics. This works both ways, and makes them less susceptible to external RF breaking into them as well.

 

Some older transmitters may not be as well screened against this kind of breakthrough. I am aware of one popular brand from a few years ago that seemed to be quite susceptible to this. Most current systems seem to be pretty bomb-proof on this front.

 

The best screening is to use a metal cased transmitter - as in days of yore! However, nearly all current systems use some kind of plastic for the case - prettier and cheaper, but not nearly as good for the purpose! Usually the plastic contains some kind of conductive material, or has a conductive layer on the inside, to make it act as a Faraday Cage: https://en.wikipedia.org/wiki/Faraday_cage   (Yay! Bring back vinyl clad aluminium transmitters! ? )

 

Most modern radios are remarkably immune to the interference from mobile phones. If they were not, we would be hearing about far more than the odd isolated incident...

 

--

Pete

 

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21 minutes ago, Peter Christy said:

Most modern radios are remarkably immune to the interference from mobile phones. If they were not, we would be hearing about far more than the odd isolated incident...

Back on topic and a very informative post Peter. ?

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Agree with Peter.

 

I use a Bluetooth dongle plugged into my Tx to feed telemetry, in particular vario tones, into wireless bud earphones so as not to annoy my fellow flyers with constant beeps etc. The Bluetooth module (from Amazon) can be seen in the bottom left of the photo.

 

Jeti telemetry includes 'Q' which monitors the signal quality (packets dropped) on the round trip Tx>Rx>Tx. The addition of the Bluetooth module & Bluetooth earpieces does not produce any measurable drop in the 'Q' and I have been using it for a couple of years flying 3metre gliders at the limit of my eyesight. 

 

The DS-24 Tx does have a full metal faraday cage case but I also have a DS-12 Tx which is plastic cased and again the module/earpiece works on that without any issue.

 

 

821DCFC8-ACA1-4D44-ADE6-A97B420E2699_1_105_c.jpeg

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