Jabiru Owners Group

Welcome to the world of Jabiru

HT interference on radio reception

Post information on Radio, Transponder, avionics, instruments and accessories including EFIS systems.
  • Advertisement

Re: HT interference on radio reception

Postby Red » Sun Sep 15, 2019 6:39 am

SkyJeep, is there anything special about the magnecor leads apart from being wire wound?.
I am getting bad ignition source interference and would like to change the HT leadS.
I cant find uncut lengths of magnecor on their website so was considering this: https://www.kingsbornewires.com/SearchResults.asp?Cat=1823

What do you reckon?
Red
Site Admin
Site Admin
 
Posts: 8
Joined: Wed Aug 28, 2019 1:05 pm
Aircraft: Easy Raider

Re: HT interference on radio reception

Postby Steevo » Sun Sep 15, 2019 2:06 pm

Magnecor will make the leads up for you if you give them the lengths. But they are not cheap and the leads alone are very unlikely to fix ignition interference problems. They may help in reducing it.

As I said in a previous post, on the Jab, there are so many places where EMI/RFI can be omitted by the Jab engine/ignition system and because it is composite rather than a metal aircraft, there is no shielding to absorb that interference so radio interference problems on a Jab are very common both from ignition and charging. I have dealt with loads over the last few years. I hate fitting avionics equipment to Jab engined composite aircraft because I know that I am almost always going to be tracking down interference issues afterwards. It is very rare to fit avionics on the Jab and it be perfect from day one.

Usually, the only way of fixing it to an acceptable level is to find where it is getting in to the system in the first place. It is almost impossible to entirely fix the source. Resistor plugs, shielded HT leads, ferrites very rarely fix the problem on their own. In-fact, I have never had them solve the problem and I have dealt with a fair few.

The biggest issue is that when avionics are put in a Jab when it’s built, the looms are just made to the minimum specification, the minimum the installation manual calls for. This is not enough on the Jab and things like wire shielding, ground points and the running of cable/coax have to be chosen very carefully. I use special equipment to find out where it is entering the system. I have a handheld spectrum analyser and a wire interference tester for these tasks. I have used magnecor cable, resistor plugs and although very good quality, I have never had them fix the issue and you just end up throwing more money at it and getting no where.

Sure, you can be lucky and the interference be at an acceptable level to the degree that it is hidden by squelch etc.
Dynon SV-2S
Funke THT800H OLED
Funke ATR833 OLED
Flight DataSystems GD-40 CO Monitoring
PoweFlarm Core
PilotAware
Garmin AERA 660 GPS and SkyDemon
MGL Xtreme EFIS
TruTrak Autopilot
User avatar
Steevo
Site Admin
Site Admin
 
Posts: 280
Images: 2
Joined: Fri Feb 06, 2015 2:56 pm
Location: Wickford, Essex
Aircraft: Jabiru J160

Re: HT interference on radio reception

Postby Stevenbonzo » Sun Sep 15, 2019 2:13 pm

Just to let you know I have ordered magnacore ht leads and king leads. When I spoke to them they were very helpful and already knew the wire lengths. I was told that most of the noise comes from the coil ( King) leads. They are sending me these as well but apparently are tricky to fit!


Sent from my iPhone using Tapatalk
Stevenbonzo
Newbie
Newbie
 
Posts: 11
Joined: Sun Aug 19, 2018 9:54 am
Aircraft: Jabiru UL 450

Re: HT interference on radio reception

Postby Red » Sun Sep 15, 2019 6:49 pm

Steevo, thanks for the advice, I was not expecting the leads to be a miracle cure but are they worth bothering with at all?.
I've made up some shielded Mag wires too and will experiment with re-routing things, the Radio and harness I fitted has come straight out of my previous aircraft and had no interference problems in that install, but it was Rotax 912 powered.
My JABIRU engine is fitted in a rag and tube plane

StevenBonzo, Thanks that makes things simpler
Red
Site Admin
Site Admin
 
Posts: 8
Joined: Wed Aug 28, 2019 1:05 pm
Aircraft: Easy Raider

Re: HT interference on radio reception

Postby Steevo » Sun Sep 15, 2019 7:15 pm

Magnecor leads are always worth it just for the quality and the performance. They may help with ignition interference. With a rag and tube aircraft, you are in much the same situation as a composite with regards to interference. You don’t have chunks of metal around you creating a faraday cage against interference.

Unfortunately with interference, there is no right or wrong answer and even with 2 exact same aircrafts wired exactly the same with the same equipment, one can suffer interference issues and the other not. Jab is especially bad as it uses mainly lawn mower parts on the ignition system that do a good job for what they do, but they were never designed with the quality and build tolerances that are specific to aircraft. You can get 2 brand new coils and one will give interference and the other one doesn’t. I have dealt with interference issues for a very long time both on my own aircrafts and many others. I have installed a fair few radio, transponders and EFIS systems and no two have ever been exactly the same when it comes to interference.

If you look across the web you will see plenty of comments like ‘fit ferrites, ‘change to magnecor’ etc etc. The reality of it is that it is seldom that simple and it’s very easy to start throwing loads of money at these things for very little benefit. And even if it did work for someone, there is no guarantee it will work for someone else.

Out of all the issues I have dealt with, I can truthfully say that the answer nearly almost always comes from the actual wiring itself. I have never solved a single issue by just adding ferrites or just changing the plugs or HT leads. I have almost always had to make some changes to the radio wiring itself or the coax along with other changes.

I have found shielded HT leads very effective but the shield has to be grounded as ungrounded shield around the HT leads will amplify the interference.

Even a rolled up ground wire behind the panel can cause interference. Every ground wire is an antenna and it only needs to be rolled up in a certain way and it will attract the exact frequency that the ignition puts out and then the interference is in the wiring. Power wires can be protected against interference via electronics and nearly all manufacturers will add that to their equipment, but ground wires cannot be protected in the same way. This is why it is recommended to have a main bus and an avionics bus so that the avionics bus can have a clean ground point and power. This is difficult to do properly in such a small aircraft with limited space.

Other things you can do is put a DC to DC converter on your avionics. This is not without it’s own issues but is a good solution to interference issues. But again, the best ones are expensive such as an MGL Avioguard.
Dynon SV-2S
Funke THT800H OLED
Funke ATR833 OLED
Flight DataSystems GD-40 CO Monitoring
PoweFlarm Core
PilotAware
Garmin AERA 660 GPS and SkyDemon
MGL Xtreme EFIS
TruTrak Autopilot
User avatar
Steevo
Site Admin
Site Admin
 
Posts: 280
Images: 2
Joined: Fri Feb 06, 2015 2:56 pm
Location: Wickford, Essex
Aircraft: Jabiru J160

Re: HT interference on radio reception

Postby skyjeep » Fri Sep 20, 2019 10:02 am

nR wire.GIF
wire lead
nR Shielded.GIF
aircraft shielded lead
nR Inductive.GIF
Bosch lead
Red, I dont think the kingsborne leads would be as good as Bosch. I have no experience with Magnecor, the other special thing about them is price.

The reason I used Bosch was they were available off the shelf and are SS wire spiral wound over a ferrite core. For HF and VHF radio suppression this is probably the best method. The SS wire has a resistance around 5k which is similar to Jabirus carbon leads (the old red ones).
They are harder to put terminals on because the centre core will not twist on to a screw end or take a wire spike like some end connectors - or coils have provision for. Further, you cant solder the wire like Jabiru do for the 6 cyl lead from the coil to make it reach the distributor.

As others have said, using lawnmower parts for an ignition, firing 4x the number of cylinders per rev, addding a car distributor as additional spark gap, not an ideal setup for RF noise. At least they used a good brand of lawnmower parts, for most of the time.

I did lots of testing and have included 3 plots here. An HT lead from the coil to a regular plug, (1) copper wire, (2) aircraft shielded lead, (3) BOSCH spiral wound ferrite core lead. Note that aircraft shielded lead actually is spiral wound wire inner conductor, so the end terminations can be threaded on.

On my aircraft (J2200 on CH701 metal aircraft) I had no problems with HT noise in the wiring. I ran shielded magneto switch leads and tested grounding each end or both without difference. The best test here is to run without mag 'P' leads connected, but remember to stop the engine by another means...

The single best improvement was the helical wound inductive core HT leads. Ferrites over the coil HT leads helped, I was not willing to attempt connecting the SS helical leads into the coil, others have done this with other type HT leads, I dont think the Bosch type would be suitable to connect there. Changing to resistor plugs helped too. I thouroughly tested the effect of resistance leads and resistor plugs and both on the coil pack voltage and found it wasnt affected.
There is no extra stress on the coils. The voltage presented to the spark plug is the same and when the spark occurs the voltage is gone.
skyjeep
Beginner
Beginner
 
Posts: 33
Joined: Wed Feb 18, 2015 7:39 am
Aircraft: Zenair CH701 2200A

Re: HT interference on radio reception

Postby Red » Sun Sep 22, 2019 5:58 pm

Good Info SkyJeep.
You mention the Bosch leads being harder to fit caps to, how did you actually manage it? and do you have details on what model/type of Bosch leads are the correct ones
Thanks


Red
Red
Site Admin
Site Admin
 
Posts: 8
Joined: Wed Aug 28, 2019 1:05 pm
Aircraft: Easy Raider

Re: HT interference on radio reception

Postby skyjeep » Tue Sep 24, 2019 7:19 am

The model of Bosch lead is in the photo on my earlier post.
They can be bought 'off the rack' at auto parts stores with workable end connectors and suitable length already made up. the plug connectors are straight and have to have the rubber boots cut off, a bend added and the Jairu angle rubbers fittted. Or, cut the plug ends off, unwind some of the spiral wire and place around the outer insulation and crimp on new angle plug ends like the Jabiru ones. this ensures connection with the wire because the connector spikes can't be relied upon to hit the wire, there is only ferrite in the middle core.
skyjeep
Beginner
Beginner
 
Posts: 33
Joined: Wed Feb 18, 2015 7:39 am
Aircraft: Zenair CH701 2200A

Re: HT interference on radio reception

Postby Red » Wed Sep 25, 2019 6:28 am

Ta SJ
Red
Site Admin
Site Admin
 
Posts: 8
Joined: Wed Aug 28, 2019 1:05 pm
Aircraft: Easy Raider

Re: HT interference on radio reception

Postby Red » Thu Jan 23, 2020 8:03 pm

Just an update, the thing that finally did the trick for me was fitting resistor pugs
Red
Site Admin
Site Admin
 
Posts: 8
Joined: Wed Aug 28, 2019 1:05 pm
Aircraft: Easy Raider

Previous

Return to Avionics, Radio, EFIS, Instruments & Accessories

Who is online

Users browsing this forum: No registered users and 1 guest