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ryansoutham(at)hotmail.co
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 Posted: Tue Jun 27, 2017 12:54 pm Post subject: Noisy radio system |
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OK, here goes.
Let me start this by saying I have tried pretty much every trick in the book to solve this issue and yes the unit is wired to a high standard with separate earth to battery, RG400 antenna cable etc etc etc.
I have a Trig radio installed in a Fairchild F24 with 145hp Warner engine. It is constantly breaking squelch even with the internal squelch wound right up. I have improved it by a huge amount but it is still pretty bad and at high RPM makes the radio essentially useless.
It is an unshielded ignition harness so this is a good portion of the problem but I wondered if anyone may have any other ideas. Oh, by the way, the noise is coming in via the antenna as it goes away when the antenna is disconnected.
Things that have improved considerably were, taking a ferrite ring and looping the antenna cable through it 4 times. more doesn't help and less doesn't help. Also changed to automotive plugs and resistor caps (5kOhm) which helped.
I get the impression that if I up the resistance a little further by going to resistor plugs or leads that we may solve the problem but I'm concerned about loading the windings in the mag to much and burning them out, would running 5kOhm resistor plugs or resistance leads load the mags too much?
I will get a reduction in spark quality which may be unacceptable and cause fouling but what do you guys think, worth a shot.
Last parting shot. The owner did the antenna install and it is an internal antenna surrounded by the steel tube fuselage and this probably isn't helping. Worth trying an external antenna, although difficult to do at this stage with a finished aeroplane (fabric), I may be able to fit to one of the wing route fairings to get a halfway decent ground plane.
Cheers,
Ryan
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Wed Jun 28, 2017 3:39 am Post subject: Re: Noisy radio system |
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Someone may correct me if wrong, but adding resistance to a circuit decreases the current. Therefore adding resistance will decrease the load on magnetos.
An external antenna is a good idea. The ground plane does not necessarily have to be sheet metal. A ground plane can be made using 6 or 8 radials of copper tape or wire that are glued to the fabric.
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