High Voltage influence on a remote control

On Sunday’s I go clay shooting on a local Skeet range that I am a member of, we have a problem that perhaps someone will be able to help us with. The high tower on one range is in close proximity to high voltage overhead cables, approx 20 feet, I am unsure whether they are 11,000 volts or 33,000 volts, not really important as to the value as according to UK Powers charts, found online, detailing their sphere of interference they are both nearly identical in their field strengths. Since we replaced the launcher in the high tower with a new unit which is actuated by a radio remote control from our shooting bases we have suffered problems where it will intermittently not fire on command, the same remote fires the launcher in the low house without problems, the low house is situated on the far side of the range well away from high voltage cables. Prior to replacing the launchers the old units were controlled by a control unit connected physically by a long cable to the launchers, no problems encountered then but it was a real pain having to drag the cable across the range every time we changed shooting positions, the old system was replaced because of mechanical problems with the launchers. The perceived problem we have is that the field (electrical that is) that surrounds these high voltage cables is causing intermittent interruption of the remote signal to the high tower, the one in close proximity to the cables. Is there any way that we can either shield or mitigate the influence of these cables, unfortunately reverting to a physical cable connection instead of the radio remote is not possible. Would placing a metal shield between the aerial wire and the high voltage cables help, I realise the field generated from the cables is all encompassing and according to the charts on the internet can still have a measurable value at up to 40 metres from the cables.

Dave W

Hi,
The field the chart you refer to is that generated by the 50Hz power. This is not what is causing the interference to the remote control which will operate on a much higher frequency. The interference will be caused either by arcing / corona on the line due to faulty insulation or, less likely, radio signal being transmitted on the lines.

The answer is to move the antenna (or receiver and antenna) closer further from the lines and closer to the transmitter. How yuo do this deends on the type of antenna. If it plugs into a coaxial connector you just need a coaxial extension cable with male and female connectors to match. If it's just a bit of wire it may be more difficult.

Moving the antenna 20 ft from he line will reduce the intereference by a factor of four.

Another option would be to use a directional antenna. A reflector plate behid the existing antenna mightt work but it depends on the frequency and the type of existing antenna. Do you have any information on or psctures of the receiver / antenna?

Robert.

Interesting problem. I have e done a lot of work with trap release radios, but never had any experience of proximity to HV power.

I assume that you have swapped high and low house radios to eliminate a reciever unit issue ?

Is there any pattern to the issue? is the reliability any worse when the transmitter is used from stand one or seven?

I would be tempted to try mounting the receiver module in the base of the high house using screened cable. This would get the height out of the picture . Although this does have the potential to increase the any interference .

Alternatively perhaps contact the radio supplier. Are they Morris Electronic units. They have always been very helpful.

Not sure it's a good idea for a tower to be so close to a HV line in the first place, but hey!

Robert's suggestion that the interference is due to a faulty insulator on the line is a good one. Try listening to an AM radio tuned between stations when standing near the power line. If the AM radio picks up loud nasty hash, there's a good chance it's due to a faulty insulator. You may be able to identify it by walking the line until the radio detects maximum racket. Anyway, if you detect interference from the line on another radio report it to whoever manages the line. As faulty insulators are bad news, they may be pleased to hear about it, especially if you know which one it is!

Another possibility is that the HV electrostatic field is directly overwhelming your electronics. (I'm told there are enough volts floating about under an HV line to strike a fluorescent tube held in your hand!) In that case the cure is to shield the electronics with an earthed box. It may also be necessary to shield any cabling and the antenna, the last being tricky.

Dave

Edited By SillyOldDuffer on 06/10/2018 20:38:19

There won't be much of an electric field that close to the power lines. Any wire carrying a time varying current radiates an electromagnetic wave. In the far field the ratio of the electric field (V/m) and magnetic field (A/m) is in the ratio of the impedance of free space, 377 ohms. In the near field the relationship is far more complex and very close to the radiator the magnetic field is likely to dominate.

The transition between near and far fields is fuzzy but around a third to half a wavelength, which for 50Hz is 6000km. So any interference issues are likely to be magnetic. Adding any ordinary metal plate will be about as useful as a chocolate teapot and less tasty. You'd need a high permeability material like mu-metal, which has it's own issues.

As has been suggested try swapping the units. Is there a coil in receiver? It may be picking up enough low frequency radiation to overload the front end amplifier even though the frequency is far removed from that of receiver.

I'm assuming you don't want to start delving into the electronics. The suggestion to mount the box at the bottom is a good one. Whatcontrol cables need to run to the top of the tower?

Andrew

As a FYi, all the clay release units I have seen are 433MHz

Gentleman many thanks for your prompt responses, unfortunately relocation of the aerial away from the cables is not practical but it may be possible to move it lower down in the high house. The make of the launchers are Laporte and without investigation I do not know the radio frequency that they operate on also substitution of high for low has not been tried, will check tomorrow whether that is feasible to prove the units integrity. We have two ranges both using Laporte equipment, the units on the other range are much older and the radio remote is much more substantial with a proper transmitting aerial mounted on the remote, the unit we have problems with, a much later version, is just a plastic box with integral keypad and no dedicated aerial, inside the box is a number of components just strung together, no location board and an altogether much inferior unit to the older unit from the other range. That I suppose is “progress” or the never ending spiral for greater profits, enough of my rant need to focus on solving our interference problem. In respect of possible arcing on the lines when we shoot in damp and misty weather the lines hum and crackle so that could be a problem. In respect of where we stand and transmit it makes very little difference to the problem whichever stand we are on which makes me think that it is probably the field from the cables swamping the receiver.

Dave W

Stuart thanks for that I will assume that ours are also 433mhz.

Dave W

Dave unfortunately the high tower on that range is where it is and geography constraints mean it ain’t going to move.

Dave W

Andrew many thanks for your response, it would appear that my thoughts about magnetic influence from the cables is probably the cause, so experimenting with relocating the receiver may help to reduce the problem, there is no requirement for cables to run up the tower, we just need to connect the launcher with receiver/ control box which could be moved lower, the launcher needs to remain where it is near the top of the tower, approx 8 - 10 feet above ground level.

Dave W

Not so sure of that, here's some numbers:

Assuming it's an 11 or 33kV line, the electric field at ground level could be as high as 700V per metre. 200V/m is 'typical', and the field strength is still 10-20V/m 25 metres to one side. The field will be even stronger if the box is only 20 feet away from the wire.

I agree about the magnetic component being difficult to shield. Might be easier to move the power line!

Dave

Edited By SillyOldDuffer on 06/10/2018 21:27:23

I am sure UK power networks will be obliging and move their pylons just far enough not to cause interference. 🤔 We won’t hold our breath then.

Dave W

I used to have a car radio that would cut out when listening to fm and driving underneath hv power lines. I had to switch it off and back on to get the sound back. I suspect that it had a front end which allowed quite high 50 hz signals through to the active devices. Generally speaking receivers haven't got any better as devices get smaller and cheaper, especially with these license-free radio remote controls. It may be that the unit simply is picking up a rather strong 50 hz signal from the electric field and has no effective filtering to keep it out of the actual receiver. Does the unit have an external antenna socket?

A 50Hz field should not affect a UHF receiver if it has any kind of tuned front end, which it should. It is possible that the 50Hz field is gettinng into the control wiring and causing issues.

It easy to find out if it's radio or wiring interference by halving the distance between the remote tranmitter and the tower for some tests. If it works at half the distance the problem is RF interference not 50Hz.

Robert G8RPI.

I'm not sure if this is a stupid suggestion but cannot one bypass the problem by using something like futaba's r/c model system.. digital and frequency hopping and good for at least 1Km line of sight??

pgk

John, the problem we are experiencing is intermittent and at varying distances around the range so I am inclined to think that cheap and cheerful electronics, I know that the remote handset is very basic inside without a dedicated aerial for transmission, allied to a probably strong and fluctuating field from the overhead cables dependent on how much current flows, is the root of our problems. I feel that without geographical changes to the range layout which is definitely not going to happen, we will probably have to live with the interference and if possible tinker with the receiver aerial to see if it mitigates the problem.

Dave W

PGK, changing the radio control system is not feasible as the current set up is supplied as an integral part of the launchers, if we butchered the equipment we would undoubtedly lose support, for what it’s worth, from the manufacturer.

Dave W

Silly question, but have you tried rotating the receiver and seeing it this makes a difference?

If you can change the aerial, a more directional one might help. Looking on t'web, most ready made 433MHz aerials are either omnidirectional or highly directional multi-bay Yagis (like an old TV aerial).

If you look online there are calculators for making a 3-element Yagi which might help by giving you a decent amount of gain (to increase the range) while still allowing yo to move around. It won't stop magnetic interference, but might make the received signal strong enough to overcome it.

Construction is just a rod split in the middle, one side to sheath one to core of your co-ax, then two rods in front and behind the middle pair arrange along an insulating or insulated support. The lengths and separation of the rods is critical, but as I say ether are calculators for this.

For 433MHz the rods will be (very roughly) a foot long.

Neil

Edited By Neil Wyatt on 07/10/2018 13:32:32