Poor radio transmission

johnM · Post by **johnM** » Fri Sep 24, 2010 5:48 pm

I found that the following item from Amazon filtered out engine ignition noise.

"Bumper 20A Noise Suppressor For Installation in the 12V Power Lead"

James L · Post by **James L** » Mon Sep 27, 2010 10:25 pm

Went for another look this evening, since I can't stop thinking about it.

Found out the p-leads aren't shielded! I don't get it - the wiring is beautifully done, but the builder didn't feel the need to shield the magneto switch wires. Weird.

Might explain the ticking noise.

James L · Post by **James L** » Wed Sep 29, 2010 10:28 pm

... except it doesn't. I fitted shielded p-leads this evening and it made no difference.

Banging head against wall.

Steve Brown · Post by **Steve Brown** » Thu Sep 30, 2010 10:53 am

Sorry to state the obvious but I assume the screens are earthed (at one end only) - if they are not earthed they will have no effect .
Mmmm, if the builder didn't realise the need to install screens, you should look carefully for other lack of good earthing points which could contribute to noise.

tnowak · Post by **tnowak** » Thu Sep 30, 2010 1:30 pm

James,

Have you confirmed if your plugs and HT leads are screened? If they aren't you are wasting your time........! Or at best it will be very difficult to minimise ignition interference.
Tony Nowak

James L · Post by **James L** » Fri Oct 01, 2010 11:24 pm

The leads are Champion supressor-type leads, the plugs are normal plugs and the caps are also unscreened.

I did a bit more experimenting this evening; moved the leads away from the airframe and tried big ferrites in various places including the coil leads, moved the antenna cable away from the airframe, fitted a 10000uF capacitor across the radio power supply. None of this had any effect.

I also bought an SWR meter and tried that out - was getting a very respectable 1.5 earthed to the airframe with no ground plane. Weirdly, the best ratio I could get with my various experimental groundplanes was 3.5, so I've left it as is.

I also tried powering the battery from an external source. It didn't make any difference, which led me to believe the interference is coming down the antenna. In retrospect this is obvious seeing as the noise is only present on transmit and receive.

I've done a bit of reading on the Jabiru forum and it sounds like the coils are to blame. Of the few people that solved the problem, there doesn't seem to be a trend any one method except everyone agreeing resistor caps and plugs do nothing.

I'm going to get a length of RG400 to replace the RG-58, just for the hell of it.

Ian Melville · Post by **Ian Melville** » Sat Oct 02, 2010 1:10 am

James Lipman wrote:I also tried powering the battery from an external source. ....

bet that caused a few sparks
I assume you mean powering the radio from an external souce

tnowak · Post by **tnowak** » Sat Oct 02, 2010 11:15 am

I can't find a picture of your radio but suspect it is a plastic cased handheld. With your plastic cased radio, unscreened leads, plugs and probably magnetos (or whatever is providing the spark) I think you are going to find it very difficult to get rid of the interference which is affecting radio performance. To prove the point try the following:

1. Place a short on the antenna input to the radio (don't transmit!). If your setup is still picking up engine interference then you know it isn't through the antenna.

2. Remove radio from aircraft and fit with stub antenna (or a bit of wire). Run engine and then walk around aircraft to see level of interference received. If significant then I don't think you can do anything to get rid of the problem.

Have you tried contacting other aircraft groups/forums which operate your model of engine for tips and advice?

Tony Nowak

Ian Melville · Post by **Ian Melville** » Sat Oct 02, 2010 6:33 pm

IIRC the IC-A21 is an alloy chassis, with alloy and plastic parts where appropriate. Shielding should not be an issue.
1 is not agood idea and proves no more than just leaving the antenna cable disconnected.
2 OK, but if you do get interference try it near another aircraft to see if you get the same.

James L · Post by **James L** » Sat Oct 02, 2010 8:31 pm

Ian Melville wrote:
James Lipman wrote:I also tried powering the battery from an external source. ....
bet that caused a few sparks
I assume you mean powering the radio from an external souce

Yep! This is obviously ruining my brain.

OK - I'm certain the A21 is an alloy case, with plastic parts. And the interference is definitely coming down the antenna - when I was doing my last set of tests, I unclipped the antenna cable from the airframe and placed the A21 out on the tailplane, leaving it still connected to the antenna cable. It still had the same amount of interference.

I'll be back down the barn tomorrow, sobbing into my pot of cable ties...

James L · Post by **James L** » Tue Oct 05, 2010 12:08 am

I went for a 30-minute cloud-dodge yesterday and the radio is way better than it was. The interference is now only obvious when the signal is weak - generally, it was pretty good. Of course, I've lost track of what I might have done to get this result, somewhat limiting the educational benefits of this thread.

Felipe Vizoso · Post by **Felipe Vizoso** » Sun Oct 31, 2010 9:30 pm

James, are you still in difficulty with the radio in your Avid? I have some experience of this issue with the Avid Flyer.

James L · Post by **James L** » Wed Nov 03, 2010 9:36 pm

Hi Felipe. I have things working a lot better now. I can still hear a ticking noise over the radio when I'm receiving a weak signal (eg. on the ground), but I can live with this. Unless, of course, you have any advice on how to eliminate it completely - that'd be great.