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Synthesised transmitters and mobile phones

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Steve Houghton14/02/2008 12:41:00
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SInce the BMFA published safety bulletin No. 6 regarding possible interference between mobile phones and syntheised transmitters, I haven't come across any follow-up information or developments. I think the bulletin came out at the end of 2004 and was published in RCM&E around December 2004. See url=http://www.bmfa.org/news/bulletins/sb6_mobiles.html]Safety bulletin 6

It was stated that the UKRCC would be carrying out further investigations and making recommendations, but I haven't heard anything more - perhaps I missed it?

I am considering the purchase of a synthesised set, possibly the Multiplex Cockpit SX, but would like to hear anyone's comments about any practical problems and precautions needed when using synthesised sets. Is it only the TX that is affected, or can synthesised RXs also be affected?

I also recall that the information published in RCM&E stated that this may be a problem with all 'programmable' sets, which I assume would include all computer sets, whether synthesised or not?

Can anyone throw any light on these matters, please, particularly those of you who are now 'synthesised'!?

Thanks, Steve.

Geoff Copping29/09/2020 10:07:39
45 forum posts
3 photos

I know this is an old thread but I think it is relevant.

Now, I must state that I aren't n elektrishun nor a tefelone enjinear so I've no idea on the causes and I'm just relating an experience I had yesterday.

I was slope soaring with a buddy. No, my buddy wasn't soaring along the slope while I controlled him, he was flying his model and I was flying mine.wink 2

Anyway, I had just set my glider and tx down next to my rucksack while I had a coffee break. I had switched off the glider but hadn't yet switched off the tx. The tx is a Multiplex Cockpit SX9, I've long been a fan of Multiplex and have never had a problem.

I suddenly heard a strange whooshing sound, similar to the sound an all-moulded glider makes when it is being flown fast across the face of the slope. However, my buddy was flying a converted Lidl so I new it wasn't that. I then realised the sound was coming from my Tx!!

I then realised that my phone was ringing in my rucksack. As soon as I answered the phone then the rushing sound stopped but, while I spoke on the phone I picked the transmitter up to turn it off and I found the right hand side of my transmitter was quite hot.

It has always been my practice to leave my phone in my rucksack at the slope, or in my car at the club field rather than in my trouser pocket just in case.

That was my first experience of mobile interference but it has convinced me that mobile phones and transmitters should not be in close proximity, certainly not Mpx SX anyway .

Geoff S29/09/2020 10:20:27
3836 forum posts
49 photos

Had the memory of the transmitter been affected? ie were the controls still set up properly for the glider?

It's certainly sensible to carry your mobile when out on the hill in a remote spot (although we managed without them for years - in my case I was often cycling miles from home incommunicado but now I feel vulnerable without my phone with me ). However it's a good idea to separate it and your transmitter as much as possible.

Are you sure the hot transmitter and the proximity to your phone are connected? Could it simply have been hot for some other reason? eg in sunlight or switched on and covered by a jacket?

Geoff

Peter Christy29/09/2020 11:05:43
1910 forum posts

Strangely enough the only case of this that I've actually witnessed also involved a Multiplex Tx, though I can't remember which type.

It was many years ago, and the model that crashed was a turbine helicopter (ouch!), being flown by a very capable and experienced pilot. I seem to recall that it was a Multiplex Tx controlling a JR receiver in the model, a strange combination, but it had previously been reliable.

A post mortem test revealed that a mobile phone in close proximity to the pilot caused the link between pilot and model to fail when the 'phone rang. Indeed, I think this was one of a couple of similar incidents that prompted the BMFA bulletin. The time period seems about right.

Tests with other transmitters didn't show the same problem (can't remember which transmitters were tested, but would almost certainly have included JR as they were very popular with heli pilots at the time).

The conclusion we came to was that plastic cased transmitters were vulnerable unless they included some kind of screening inside. Not all do!

Personally, I've never liked plastic transmitters, purely from an engineering point of view. In days of yore, transmitters were made of folded sheet metal, which not only provided good protection against outside interference, but also made a much better "earth" contact with the pilot, improving the poor radiation pattern from telescopic aerials.

However, as is so often the case (Boeing 737-MAX?) economics took priority over engineering and we are where we are!

--

Pete

Geoff Copping29/09/2020 11:06:20
45 forum posts
3 photos
Posted by Geoff S on 29/09/2020 10:20:27:

Had the memory of the transmitter been affected? ie were the controls still set up properly for the glider?

It's certainly sensible to carry your mobile when out on the hill in a remote spot (although we managed without them for years - in my case I was often cycling miles from home incommunicado but now I feel vulnerable without my phone with me ). However it's a good idea to separate it and your transmitter as much as possible.

Are you sure the hot transmitter and the proximity to your phone are connected? Could it simply have been hot for some other reason? eg in sunlight or switched on and covered by a jacket?

Geoff

Hi Geoff, I had 2 models with me and they both passed a thorough check . As for the heat, I did wonder if it was sunlight but it subsided quickly when I turned it off and didn't recur when I turned it back on again, even though it was still in sunlight. It coud have just been coincidence because I can't think what may have caused it, I've certainly never noticed any heating of the Tx before.

Steve J30/09/2020 06:54:24
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2085 forum posts
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Posted by Peter Christy on 29/09/2020 11:05:43:

Personally, I've never liked plastic transmitters, purely from an engineering point of view. In days of yore, transmitters were made of folded sheet metal, which not only provided good protection against outside interference, but also made a much better "earth" contact with the pilot, improving the poor radiation pattern from telescopic aerials.

Personally, I would rather fly with a transmitter that is compliant with modern EMC standards.

Peter Christy30/09/2020 08:34:25
1910 forum posts
Posted by Steve J on 30/09/2020 06:54:24:

Personally, I would rather fly with a transmitter that is compliant with modern EMC standards.

The problem with modern EMC standards is that they are mostly designed to stop the transmitter interfering with other users.

In this case, it is a transmitter being susceptible to interference from other users.

Enclosing the electronics in some kind of Faraday cage (ie: a metal box) not only protects a transmitter from external interference, but also reduces stray radiation from it. Not all of the output from a transmitter goes up the aerial!

Many "plastic" transmitters do include some kind of screening - either a coating sprayed on the inside of the box, or enclosing critical components inside internal metal compartments - but such measures inevitably increase production costs. And none of us wants to spend more than we have to!

The best solution remains a metal cased transmitter. Sadly, these are now a thing of the past!

--

Pete

Brian Cooper30/09/2020 08:55:06
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605 forum posts
27 photos

I was test-flying a model with Multiplex 2.4Ghz radio for a clubmate recently. . About two minutes into the flight, the ailerons reversed themselves. . surprise . . The only thing we could put it down to was my buddy had a mobile phone in his pocket.

Flying with any function reversed is certainly a challenge but the model made a tidy landing back on the grass strip.. yes

Strangely, the close proximity of a phone to other makes of modern transmitters doesn't seem to affect the Tx................. so far.

Edited By Brian Cooper on 30/09/2020 08:58:02

J D 830/09/2020 08:56:05
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1631 forum posts
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Pardon if I am missing something here but I thought it was just the RX's that are synthesized. I still use my Futaba FF7 35 band with synthesized RX's [ no crystal ] Is that something different ?

John Lee30/09/2020 09:34:50
807 forum posts
94 photos
Posted by Peter Christy on 30/09/2020 08:34:25:

The best solution remains a metal cased transmitter. Sadly, these are now a thing of the past!

 

Well, not with the higher end Jeti transmitters. Their cases are still machined from a solid slab of aluminium. Video

Edited By John Lee on 30/09/2020 09:35:38

Peter Christy30/09/2020 10:17:09
1910 forum posts

And as I said: "Such measures inevitably increase production costs"!

Very nice, if you can afford one, but the receivers are also very expensive and the transmitters appear even more complex to program than OpenTx! (One of my flying buddies has one!)

Well out of my price range, I'm afraid!

--

Pete

Dickw30/09/2020 10:58:58
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767 forum posts
103 photos
Posted by J D 8 on 30/09/2020 08:56:05:

Pardon if I am missing something here but I thought it was just the RX's that are synthesized. I still use my Futaba FF7 35 band with synthesized RX's [ no crystal ] Is that something different ?

Some brands did both synthesized Rx and synthesized Tx. I could swap channels on 35MHz without changing any crystals with my Multiplex.

Dick

Doctor Chinnery30/09/2020 11:53:37
76 forum posts

I am still the proud owner of one of the first batch of Mpx Cockpit SXs into the UK, it's always been faultless. Regarding the possible interaction of cellular phones and my Cockpit, what interaction? Having a business which required me to be contactable by my clients and/or staff 24/7 my phone was always within reach or about my person - when my plane was actually in the air, I had a bud in my ear and a mike clipped to my shirt collar - and I was never aware of any obvious 'glitches' before during or after a call - though my concentration on the plane could have been temporarily compromised! Standard reply - "I've got my hands full, I'll phone you back in a minute". Then land and return the call - and especially if it was a Sunday afternoon - pack plane and gear into the car and get back to earning a crust! ( If it's your business you're never off duty. )

Frank Skilbeck30/09/2020 13:44:30
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4847 forum posts
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A couple of members at our club have got motion detectors at home which set off their phones, so you will be flying with them and hear a message "motion detected", don't worry they say it will just be the wife going into the garden.

I often fly on the slope with my phone in my pocket, never had any issues with programmable radios from Futaba, Spektrum, Multiplex and Jeti, while using Blackberry and Sony Android mobile phones.

BTW if your transmitter is somehow getting hot then it would need power to do this, so you would probably see the battery volts/remaining mins dropping off too.

Be interesting to see what phone was causing the interference too.

Not sure what Multiplex Tx Brian was using, but if it was a Royal Pro/Sx or Profi you can reverse the aileron input in the aileron mixer if you enter the aileron mixer menu, highlight the aileron input and then push the Rev/Clr button, but that would take a few deliberate button pushes to get there. But it would be one thing to check on the radio in question, if the aileron input has gone from +100% to -100% that could be the cause. Otherwise if it has dual ailerons you'd have to reverse both aileron servo simultaneously.

J D 830/09/2020 13:51:13
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1631 forum posts
87 photos
Posted by Dickw on 30/09/2020 10:58:58:
Posted by J D 8 on 30/09/2020 08:56:05:

Pardon if I am missing something here but I thought it was just the RX's that are synthesized. I still use my Futaba FF7 35 band with synthesized RX's [ no crystal ] Is that something different ?

Some brands did both synthesized Rx and synthesized Tx. I could swap channels on 35MHz without changing any crystals with my Multiplex.

Dick

Thanks for the info. Cheers, John.

Nigel R30/09/2020 13:56:39
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4201 forum posts
703 photos

"The only thing we could put it down to was my buddy had a mobile phone in his pocket."

The likelihood of RF interference causing a change to the SW functionality of this specific a nature is very close to zero.

Far more likely is a user error during setup of the model on the TX, or simply a defect in the TX software.

Bob Cotsford30/09/2020 15:17:47
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8801 forum posts
494 photos

It wouldn't be hard to set up an odd rate with -ve weight on some systems, or a flight mode, or a special function - user error is plausible to say the least with the more complex operating systems.

Nigel R30/09/2020 15:45:24
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4201 forum posts
703 photos

Precisely Bob. I'd say the single most likely cause, not just plausible.

Failure of data storage induced by radio frequency energy is, how to put it, not likely.

Occam's razor, etc.

Geoff Copping30/09/2020 16:21:04
45 forum posts
3 photos
Posted by Frank Skilbeck on 30/09/2020 13:44:30:

A couple of members at our club have got motion detectors at home which set off their phones, so you will be flying with them and hear a message "motion detected", don't worry they say it will just be the wife going into the garden.

I often fly on the slope with my phone in my pocket, never had any issues with programmable radios from Futaba, Spektrum, Multiplex and Jeti, while using Blackberry and Sony Android mobile phones.

BTW if your transmitter is somehow getting hot then it would need power to do this, so you would probably see the battery volts/remaining mins dropping off too.

Be interesting to see what phone was causing the interference too.

Not sure what Multiplex Tx Brian was using, but if it was a Royal Pro/Sx or Profi you can reverse the aileron input in the aileron mixer if you enter the aileron mixer menu, highlight the aileron input and then push the Rev/Clr button, but that would take a few deliberate button pushes to get there. But it would be one thing to check on the radio in question, if the aileron input has gone from +100% to -100% that could be the cause. Otherwise if it has dual ailerons you'd have to reverse both aileron servo simultaneously.

It was a Samsung Galaxy J5.

I have sometimes forgotten to take my phone out of my pocket and this is the first time I've ever experienced any interference over many years.

I've no idea what caused it but, now I know it can happen, I will not chance it if I can help it.

As we used to say in my sky-diving days " If there's a million to one chance that something can happen then one day it will"!!

Tomtom3930/09/2020 17:18:19
696 forum posts
1 photos

Peter C,

I use the Jeti system. The programming is intuitive and not difficult to use. There are also some excellent videos on Youtube. I 'd say the basic modes ie to set up and fly a model from scratch , are not dis-similar to what you would do on a DX6 . It is pretty straightforward. What you are paying for is the flexibility and quality of the system . Best move I made, which was when the first 16's came out. I have the 24 , still learning.

It was either that ,a new handbag or look to dust off my old Fleet gear.

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