Com. Antenna location  

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bennisv
(@bennisv)
Active Member
Joined: 6 months ago
Posts: 9
27/07/2018 1:31 am  

Hi   Have been battling with radio interference for long time - the com reception is fine but when transmitting a loud (while engine is running) squealing noise pops up and people hardly read me due to this noise. The noise increases as RPM is increased.  I am using the Jabiru 2200 engine and the radio is icom A200. My ultralight is X'air Hawk.  The Antenna is god earthed and the SWR is 1:1,7. The interference is not coming through 12 volt line in aircraft - have checked that by bypassing using external 12.v battery .  I have tested the output of transmission by using Dummyload  with fine result - no noise in transmission.  The antenna is in my opinium the fault as it seems to pick up RF signals from the engine and reflects to radio while transmitting. Yes I have checked the wirings and shielding and lines in and from the engine. Currently the location of my antenna is just aft over the cabin and my next step is to move the antenna to the tailsection in case that would minimize the RF interference (as far away from the Engine). What I see on most of the Jabiru aircraft is that the com antenna is located on tailsection - must be reason for this ? or is it just cosmetic ?


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Doug Smith
(@doug-smith)
Member Admin
Joined: 8 months ago
Posts: 45
13/08/2018 1:14 pm  

Hi!

In a fibreglass aircraft RF noise is always an issue, so putting the standard antenna down inside the tail was both a cosmetic and a functional decision.

Sounds like you've done a great job hitting all the usual suspects... actually that's about the point at which I'd usually go begging for an avionics tech to look at the aircraft for me!

One thing, have you tried different brands of headsets?  I've had several radios which, for one reason or another, just don't like certain brands of headsets.  In your case it sounds like maybe the side tone or the signal amplification out of the headset is incompatible with the radio and it's squealing out the signal.  Some radios have adjustment for side tone in their menus, others it's a "break the warranty seal and adjust with a screwdriver" type of job.  Either way, it'd be worth looking at - and trying a few totally different brands of headsets would also definitely be worthwhile.  

Best Regards,

Doug.


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bennisv
(@bennisv)
Active Member
Joined: 6 months ago
Posts: 9
18/08/2018 11:37 pm  

Hi Doug

Thanks for your input here - yes I did try some different headsets and I also could manually make some adjustments of mike gain and side tone in radio but the results where not quite enough. Finally I made a test which I DID try before (without positive result) and that was to disconnect the Intercom (AVCOMM AC-2EX INTERCOM) from radio and connect the headset "direct" to radio and the squealing went away.  I am not sure why it did not work in previous test but I suspect I used wrong adapter cables from headset to radio. The Intercom type is a fine unit and not sure what is happening there but got it borrowed and saw that lines from Intercom to radio (one meter long) was not the original line (some homemade connection assembly). Perhaps the "homemade lines" where incompatible and could have made the problem.
I will get new Intercom - at least I think I am on the right track and saving money not have to buy new radio he he.


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Doug Smith
(@doug-smith)
Member Admin
Joined: 8 months ago
Posts: 45
27/08/2018 12:04 pm  

That sounds good... I'm not familiar with that particular intercom but arguments between intercom and radio are not that unusual, particularly if there are any issues with the loom.  I've seen systems where excess length in the loom was coiled up inside the instrument panel right next to the radio and that sort of thing can cause a lot of trouble, especially if the wires are not shielded. 

And at the least we're replacing the cheaper parts first!

Doug.


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