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Synthesised transmitters and mobile phones

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Phil Green30/09/2020 17:43:10
1661 forum posts
344 photos

A thought...
many drone transmitters rely on an attached mobile phone, the phone is an integral part of the system smiley

Peter Christy30/09/2020 19:30:12
1908 forum posts

Tomtom: I hear what you are saying, and really don't want to get into a "BrandX Vs BrandY", so I'll confine myself to saying that I've never had a problem programming OpenTx. My comments were based on watching a flying buddy struggling to set up crow braking, but he does tend to over-complicate things! wink

Coming back to the original topic, mobile 'phone interference has been repeatedly demonstrated on some well known brands of equipment. Not all systems suffer from it, but some do - hence the BMFA bulletin on the subject.

The problem is that its not even just a brand issue, as some models within a brand range appear susceptible whilst others do not.

Mobile 'phones do put out very powerful, pulsed signals on occasions, and will break through into anything that is not well shielded. I'm sure we've all heard that rat-a-tat-tat noise on a stereo or computer speakers at some time.

That bulletin is still as valid today as it was back in the days of 35 MHz. I had hoped that 2.4 GHz equipment would, by its nature, be better screened, but it would appear that not all of them are!

Be careful out there!



Steve Houghton30/09/2020 22:15:31
588 forum posts
438 photos

Thanks to Geoff C for bringing my old thread back to life, and to everyone who has posted interesting comments.

My immediate need for advice has now largely passed, since I invested in a 2.4GHz JR DSX-9 a few months after the opening post. I'm now stuck with old DSM-2 technology, lots of matching receivers, and an expired manufacturer. However, for the timebeing the DSX-9 is working fine and is a great TX to programme and handle, as long as it remains reliable and operational.

Shortly before JR folded, I also bought a JR XG-7 with a couple of DMSS receivers, and was once again left with unsupported technology. Ah, such is life!

jrman30/09/2020 23:13:23
423 forum posts
3 photos

Steve, JR hasn't folded. It's under new ownership (RC Depot). It's still made in the same Malaysian and Japanese factories as before. Unfortunately it's not very well represented in the UK.

Peter Christy01/10/2020 09:13:50
1908 forum posts

And the prices have gone through the roof! (I, too, have lots of JR gear 2.4 & 35, still all working well!)



Steve Houghton02/10/2020 21:41:06
588 forum posts
438 photos

Jrman, thanks for the info - I didn't know they were still manufacturing, I thought they were just selling off old stocks.

Pete, yes I've now seen some JR/DFA prices at Probuild - wow!

jrman02/10/2020 23:25:04
423 forum posts
3 photos

Steve, Very little stock in the UK. I get most of my needs from here:


Martyn K03/10/2020 02:15:15
5102 forum posts
3701 photos

Back to the topic.

Radio transmission depends on the generation of an Electro Magnetic wave. In normal use the Electric field is dominant. However, when a transmitter is held in very close proximity to an electronic circuit, the magnetic field becomes dominant and can cause havoc. It is not interference in the conventional sense due to poor selectivity of a receiver or a noisy and wide transmission but simply due to induced energy from one object to another. 

The fix is very simply, don't place your mobile phone (which is always transmitting) next to an electronic circuit of an sort.

Edited By Martyn K on 03/10/2020 02:16:11

MattyB03/10/2020 08:56:57
2322 forum posts
43 photos
Posted by Steve Houghton on 02/10/2020 21:41:06:

Jrman, thanks for the info - I didn't know they were still manufacturing, I thought they were just selling off old stocks.

Pete, yes I've now seen some JR/DFA prices at Probuild - wow!

At those RX prices and with no new TXs I can’t see them surviving for long. They are just too far behind the competition in terms of technology and market share to catch up at his point.

Julian Thacker14/10/2020 20:55:32
38 forum posts

This post applies to 2.4 gear rather then 35MHz. In my club we have had a single occurrence of possible mobile phone interference with a transmitter, in this case while in flight. The model was being flown by an experienced and capable pilot when his phone rang in his pocket (this was prior to the BMFA recommendation). As the phone rang his model went out of control and crashed.

The two possible explanations I have come up with are a) the phone did interfere with the tx operation, b) the pilot's attention was diverted by the phone tone and he lost concentration and control of the model. My money is still on the 2nd possible cause but the pilot is certain his control of the model was not affected by the phone call. Probably irrelevant but the radio was a Multiplex (I have no idea which model but it was 2.4).

Purely out of interest I recently tested another radio by putting it into rage test mode, walking out about 100 metres, and then calling the model restrainer on my mobile. We had a conversation with both of us holding our phones as close as we could manage to the tx at my end and the rx at his end and the model responded to all commands faultlessly. I am not claiming this was a scientific test but it did reassure me that my radio appeared to be fairly resistant to interference from my and my mate's mobile phones. Obviously another phone may have had a different effect. Oh, I have metal cased and plastic cased txs; this test was with a plastic cased tx.



Edited By Julian Thacker on 14/10/2020 20:56:52

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