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[GG]

When installing and testing the rudder servo in a new model some intermittent interference was observed in the garage cum workshop I use.  After checking the batteries and connections, all seemed well so the model was checked out on the garden pond where it performed perfectly.  Problem sorted, or so I thought.


Testing the model a few days later in the workshop and problem had returned but, again it performed flawlessly on the pond.  "Damn RC gear" I thought "it doesn't like working indoors!". Then it struck me that this might actually be true.


Some years ago a similar situation had occurred in the spare bedroom that I call my "office" but Mrs Guest has a less complimentary name for it.  When checking the RC gear before going on a sailing session, the rudder servo would give a periodic twitch, an exact few seconds apart. When sailing this model there was never any rudder twitching apparent. At the time I put this down to an internal interference effect, possibly the transmitter signal being reflected by something or even the wireless alarm system we had installed..?


Since then "wireless" devices have grown greatly in number, the laptop I'm currently typing on is one. No doubt all these things have been designed to avoid interference with our RC models, but as Alexander Pope once said;
"Whoever thinks a faultless piece to see,
     Thinks what ne'er was, nor is, nor e'er shall be"


Anyone else experience this effect...?


Glynn Guest

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[C-3PO]

Hi Glynn,

The reciever will be pretty sensitive to RF - if you have the radio transmitter within a few meters of the receiver in the workshop you may well be overloading the receiver front end resulting in odd behaviour.

Regards
C-3PO

[Netleyned]

Fluorescent lighting affects some sets indoors.
Ned

[HMS Invisible]

Fluorescent lighting affects some sets indoors.
Ned

That is true. Electronically ballasted fluorescent lights and computers are known to be a problem.
I have tried both as a convenient source to induce glitches in product proof tests but replaced all compact fluorescent lamps a long time ago.

Model submariners who still use 40MHz (simple PPM is still common) would do well to test in excess of five metres away from a source before deciding to rip out brushed motors.

[GG]

Good points, I now recall that the workshop had a fluorescent strip light when I encountered the servo interference.  But, this wouldn't explain the very regular rudder servo twitching in my "office".


Still, the damn things work OK when sailing so I'm not worried, just curious...


Glynn Guest 

[malcolmfrary]

A common result when checking out radio interference in my local area was the CAA radar inland from what was the airport.  On many early video recorders this manifested itself as a series of "raspberrys" every 6 seconds, as the antennas rotated.  The usual cure was to set the output link on the recorder to a different channel and retune the telly. 
Driving past the site in a car with speakers in the back would give the same problem.  This was the speaker leads picking up the signal and feeding it into the semiconductor output stages of the amp which detected it and duly amplified it.  If a servo lead picks up a signal and passes it into the output of the radio, the semiconductors in there might do the same job, but as described, this should show on any channel.


If the effect was noted using an AM radio, then any spurious RF signal in what should be the quiet part of the signal window has a fair chance of being resolved as the start of a new information window, and will be passed to the first channel, usually the one with the steering servo plugged in.  If it is a strong signal, trying to selectively tune it out doesn't work - its brute force and ignorance time.  Or if it only happens in one place, avoid the place when doing that job.
Alternative procedure - be in the room, have it happening, progressively turn stuff off.  Somewhere along the line, provided that it is something that you can access, it should stop.

[GG]

Ah.... more good ideas but the nearest airport is many many miles away so I don't think they were the culprit.  We used to have a big Government Communication center nearby but it closed down some time ago, unless it's still secretly operating underground?


To be honest I didn't notice this effect when giving all my RC gear a check, something to keep me occupied during the Covid lockdown.  Although this was just a quick operation, plug together, switch on, wiggle the sticks and on to the next outfit, so could have been missed.


As an aside, I don't get excited about old RC gear, the mythical "Golden Age of RC" sort of thing, but I was impressed that some items which must be over 40 years old, still worked perfectly.


Glynn Guest

[malcolmfrary]

Many years ago a boss of mine said "There is no such thing as an intermittent fault" thus confirming what many of us thought about him.  Had he expanded his spouting to say that some permanent fault conditions might need the right circumstances to show themselves.
However something happening periodically must have a cause.  It might or might not be worth finding.  But - is it just the one model? Is it really just one servo or any servo in that channel?  Does it happen with a different receiver? Or a servo tester?
Once the cause is known, it is usually very obvious and logical.


The radar thing wasn't "that" local, and it wasn't the airport radar which was a scratty anaemic little thing. This was the one that did NW England, and had the power to give it that reach.  My workmate who made the discovery for himself lived in Fleetwood, as the pig flies, a good 10 miles.  Confirmed it by ringing them up, chatting with them, and them offering to change over transmitters.  So he tweaked his VHS video to a channel that they were not going to transmit on.  No idea what they transmit on now, they have totally different arrays.  Side note - they complained of interference once.  A local biscuit factory over 2 miles away from them had a nice new continuous microwave oven.  When it jammed once, a workhand poked the offending lump free with a stick, and dislodged a baffle or two.  It was a bit unfortunate that the oven was in the same band as the radar and in line with it.


Since the indoor problem is very local, it must be something caused by something very local, possibly in the same room.  Knowing what it is/was helps avoid running into it later, as well as satisfying curiosity.  And, of course, it might be something worth finding.

[CGAux26]

I have seen the servo twitch when binding a new RX to my Spektrum TX.  It happens on my bench with fluorescent lights all around, but does not seem to be caused by the lights.  Moving the TX 6 ft. away from the boat stops it.