ht lead sheilding

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paul bradberry
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ht lead sheilding

Postby paul bradberry » April 29th, 2010, 7:09 pm

HI
Trying to locate some copper braid suitable for sheilding a zenoah ht lead as modern coaxial cable doesn't have the correct density of braid can anybody help?

Many Thanks

Matt Harrowven
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Re: ht lead sheilding

Postby Matt Harrowven » April 29th, 2010, 9:11 pm

Shamelesly lifted from a quote on RCMF from Dr Keith Mitchells Radio Installation booklet

HTH

You will need around 7-8 metres of TV co-axial aerial, as binding the lead takes a surprising amount of material. Strip-off the outer plastic sheath and slide off the copper, braided screen - which is the part which is to form the screen. Flatten this length of braid and at its centre form a loop in it at right angles to its length. This loop should be long enough to extend from the base of the H.T. lead where it exits the magneto block, to a convenient screw point on a main conductive part of the motor e.g. crankcase, fin or engine mount. From the exit point on the magneto block one half of the copper screening lead is wound in a clockwise direction up the H.T. lead. After the first turn secure it to the lead with a small cable tie or strip of electrical tape; this will help keep the whole assembly in place as you progress. Try to keep the turns together minimising air gaps - the job, I’ll admit, is fiddly, but keep patience. It gets particularly difficult at the plug cap but this has to be covered and this is where you will notice your seemingly generous length of braid being ‘gobbled up’ at an alarming rate. Once at the end of the cap, trim and secure with a turn or so of electrical tape. Now to the other half; this needs to be wound up in an anti-clockwise direction over the top of the first half, again ensuring that all air gaps are filled (NB air gaps in electrical shielding are like holes in water pipes, EMI searches ‘em out). Once at the cap end, trim and then bind the whole lot with electrical tape all the way down to the magneto. Don’t despair if it doesn’t look particularly neat - it’s effectiveness that’s important here and what you have tried to achieve is a conformal copper sheath which will reduce radiated EMI which comes not only from the lead but the unshielded ceramic of the plug itself. Complete the job by earthing the ‘loop’ on the motor body.

Matt 3066
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Bob Thompson1894
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Re: ht lead sheilding

Postby Bob Thompson1894 » April 30th, 2010, 5:52 am

Is this an answer looking for a problem? Never had the need to do this before, not had any trouble....

frederick barlow
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Re: ht lead sheilding

Postby frederick barlow » April 30th, 2010, 10:11 am

you could try some de soldering braid but the widest i can find is 2.5mm wide heres a link
http://www.maplin.co.uk/Module.aspx?moduleno=33702

paul bradberry
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Re: ht lead sheilding

Postby paul bradberry » April 30th, 2010, 5:35 pm

Thanks gents for the replies much appreciated .
Regards
Paul :D

Dave Hayfield
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Re: ht lead sheilding

Postby Dave Hayfield » May 1st, 2010, 9:47 pm

Yes Bob I agree, have had many Zenoah engines operating with several different radio systems and never had to use any shielding. If interference is present I would be tempted to look for another cause such as the correct spark plug.
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paul bradberry
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Re: ht lead sheilding

Postby paul bradberry » May 2nd, 2010, 9:16 am

Hi Dave
The problem i have is only appearing on the throttle servo which is located on the bulkhead behind the engine,The engine is a z26 when it is running and i perform a range check i can only walk away approx ten feet and the throttle servo starts jumping i have tried changing the servo/leads all to no avail,I have az23 which already had sheilding i fitted this to the 26 and the interference stopped?.
Regards
Paul

Bob Thompson1894
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Re: ht lead sheilding

Postby Bob Thompson1894 » May 2nd, 2010, 10:05 am

In this case a piece of ali foil fastened to the bulkhead behind the servo should suffice. The servo lead should be braided, this will also help. I try not to put servos as close as that, vibration can cause problems.

paul bradberry
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Re: ht lead sheilding

Postby paul bradberry » May 2nd, 2010, 10:12 am

Bob Thompson1894 wrote:In this case a piece of ali foil fastened to the bulkhead behind the servo should suffice. The servo lead should be braided, this will also help. I try not to put servos as close as that, vibration can cause problems.

Hi Bob
Tried this morning with a new spark plug and all servos started juddering Regards Paul

Chris Lane
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Re: ht lead sheilding

Postby Chris Lane » May 2nd, 2010, 11:12 am

Paul, are you on 2.4gHz or 35mHz please? And presumably your transmitter and receiver were on during these checks !

Chris Lane

paul bradberry
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Re: ht lead sheilding

Postby paul bradberry » May 2nd, 2010, 11:19 am

Chris Lane wrote:Paul, are you on 2.4gHz or 35mHz please?

Chris Lane

Hi Chris
I am on 35mHz Futaba Regards

Tony Collins 1073
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Re: ht lead sheilding

Postby Tony Collins 1073 » May 2nd, 2010, 11:32 am

Its possible that as your servo is so near to the engine that the RF is getting into the servo signal wire and then into the receiver. Sometimes the magic bead as used on long wire systems can sort this. I always use the system of passing the servo pulse through an inverter ic which when inverted again isolates the servo electronically and boosts the signal pulse.
It is a simple little circuit which I can let you have if you wish. It simply fits between the servo and the receiver as close to the receiver as possible. I have been using it for ten years without a glitch, and my electronic ignition system is unscreened.

Dave Hayfield
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Re: ht lead sheilding

Postby Dave Hayfield » May 2nd, 2010, 12:58 pm

Must admit that I have never fitted a throttle servo that close to the engine but before doing expensive things a ferrite ring on the servo lead might be worth a try.
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paul bradberry
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Re: ht lead sheilding

Postby paul bradberry » May 2nd, 2010, 2:17 pm

Thanks Tony/Dave Will try a ferrite ring on the throttle servo first if that doesn.'t work i will move the servo.
Regards
Paul

Michael Ronan
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Re: ht lead sheilding

Postby Michael Ronan » May 3rd, 2010, 11:38 am

Hi, I needed to make up an extension to a Zenoah 62 Easy Start lead. I could not get a good quality copper braiding. I then went along to my local hydraulic pipe suppier and told him my problem. He found some stainless steel braiding on synthetic rubber hose. He cut off a metre of hose and I was charged 50 pence. I then bought a plug and socket, identical to the original Easy Start plug and socket, and threaded the stainless steel braiding over four different coloured wires similar to the original. It works perfectly and have enough overv to make another if necessary. Hope this helps.

paul bradberry
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Re: ht lead sheilding

Postby paul bradberry » May 5th, 2010, 6:27 pm

Hi Guys
Moved throttle servo away from engine bulkhead it is now ten inches away from the engine also fitted a ferrite ring on the servo lead aand i still have interference?
Regards Paul

Tony Collins 1073
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Re: ht lead sheilding

Postby Tony Collins 1073 » May 5th, 2010, 9:46 pm

Where did you locate the ferrite ring Paul? It should be as close to the receiver as possible. That is the only place for it to go. If you have used an extension lead for the servo then the ring must fit on the extension lead next to the receiver. I still think isolating the servo with an inverter ic is far superior to rings.

See this link. http://www.laureanno.com/RC/noisetrap.htm
Last edited by Tony Collins 1073 on May 6th, 2010, 6:45 am, edited 1 time in total.

John Greenfield
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Re: ht lead sheilding

Postby John Greenfield » May 6th, 2010, 6:23 am

Hi all

Just a thought but it may not be an interference problem, it could be a damaged servo. Before going to far, try plugging another servo into the throttle channel to see if the problem is still there.
I have seen this sort of thing before and it was the servo that was the problem (for what ever reason !?).

Worth a try.

John

Chris Lane
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Re: ht lead sheilding

Postby Chris Lane » May 6th, 2010, 7:46 am

Any guidance on what size ring and how many turns please - these things are HEAVY ? Chris Lane

Tony Collins 1073
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Re: ht lead sheilding

Postby Tony Collins 1073 » May 6th, 2010, 8:40 am



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