Strange radio problems
Thread Starter
Join Date: Dec 2011
Posts: 2,460
Likes: 0
Received 0 Likes
on
0 Posts
I think the crackling was the sound of static charge, picked up by the aircraft as a whole, arcing across (flashing across) the non-conductive elevator bearings to the elevator, from which it escaped via the static wicks as normal.
That's my guess.
But yes it could have been the other way around i.e. static charge picked up by the elevator arcing across its bearings to the airframe, from which it got dissipated via the static wicks on the flaps, and the (somewhat less effective) static wicks on the ailerons.
The COM2 antenna is a lot closer to the elevator than the COM1 antenna, hence...
No idea. These radios are damn complicated digitally synthesised jobs.
That's my guess.
But yes it could have been the other way around i.e. static charge picked up by the elevator arcing across its bearings to the airframe, from which it got dissipated via the static wicks on the flaps, and the (somewhat less effective) static wicks on the ailerons.
The COM2 antenna is a lot closer to the elevator than the COM1 antenna, hence...
what about the 'only detectable when there's carrier' part
Join Date: Apr 2008
Location: Cilboldentune, Britannia
Posts: 555
Likes: 0
Received 0 Likes
on
0 Posts
It's quite noticeable that the later PA28 types (Warriors/Archers) that I've come across recently (and with glass cockpits) seem to have many more bonding and static wicks than previous.
Join Date: Jan 2010
Location: Texas and UK
Age: 66
Posts: 2,886
Likes: 0
Received 0 Likes
on
0 Posts
I did see in the late 70's a 172 get hit by a lightening (hit the wing) on on short finals. The ailerons were welded solid on the side which took the strike. The only evidence of the strike (other than the welded aileron) was the small area of discolouration on the wing surface.
I guess no amount of bonding strap would have helped with that, but static discharge is a different mater.
Well done Peter
I guess no amount of bonding strap would have helped with that, but static discharge is a different mater.
Well done Peter
Join Date: Feb 2006
Location: Hanging off the end of a thread
Posts: 33,450
Received 3,192 Likes
on
1,339 Posts
I would make sure the jack plugs in the panel are tight and haven't worked loose, also clean your headset plugs, I use a little bit of fine scotchbright.
Join Date: Nov 2007
Location: Too close to EASA
Posts: 408
Likes: 0
Received 0 Likes
on
0 Posts
Hey Peter - good fix!
It seems like a British avionic engineer can actually diagnose a problem correctly (post 11) - I thought you believed only Americans could do anything right.
You know where we are when you finally want the PRNav upgrade - and not for £40K!
It seems like a British avionic engineer can actually diagnose a problem correctly (post 11) - I thought you believed only Americans could do anything right.
You know where we are when you finally want the PRNav upgrade - and not for £40K!
Thread Starter
Join Date: Dec 2011
Posts: 2,460
Likes: 0
Received 0 Likes
on
0 Posts
You were right, wigglymap 
BTW I never suggested UK avionics shops are worse than US ones.
It is instrument overhauls, particularly gyro ones, which I would never do in the UK.
BTW I never suggested UK avionics shops are worse than US ones.
It is instrument overhauls, particularly gyro ones, which I would never do in the UK.
Update to my howling problem:
Mine is a wooden aircraft. I had re-located the aerial inside the fuselage and this was the cause of the problem. When I re-located back outside the problem went away.
Mine is a wooden aircraft. I had re-located the aerial inside the fuselage and this was the cause of the problem. When I re-located back outside the problem went away.
Thread Starter
Join Date: Dec 2011
Posts: 2,460
Likes: 0
Received 0 Likes
on
0 Posts
Interesting... how do conventional VHF aerials work on a wooden hull?
Surely they need a ground plane? At least around the aerial base.
Otherwise what you have is a length of coax whose screen suddenly ends in nothing, and the inner conductor goes to the base of the aerial. RF stuff was never my strong area (I used to build pirate ratio transmitters in the late 1960s, with a pair of 807s; we even considered powering it from the 700V DC train rail
) but this doesn't seem right. The cable screen needs to go to that ground plane.
Surely they need a ground plane? At least around the aerial base.
Otherwise what you have is a length of coax whose screen suddenly ends in nothing, and the inner conductor goes to the base of the aerial. RF stuff was never my strong area (I used to build pirate ratio transmitters in the late 1960s, with a pair of 807s; we even considered powering it from the 700V DC train rail
) but this doesn't seem right. The cable screen needs to go to that ground plane.
Join Date: Nov 2007
Location: Too close to EASA
Posts: 408
Likes: 0
Received 0 Likes
on
0 Posts
On a wooden or composite airframe, the ground plane foe a uni-pole antenna is normally either metallic foil or mesh inside the fuselage. The ground plane should be at least 1/4 wavelength radius and the antenna should be centred to avoid becoming directional. The core of the co-ax goes to the antenna which is insulated from the ground plane and the screen connects to the ground plane. It's also possible to use a 1/2 wave dipole -typically a NAV antenna, or a Comm antenna inside the fin. In this case, the connection to the co-ax uses a matching balun cable and the co-ax core doesn't actually connect to either leg of the dipole.
What I know about radios can be written on the back of a fag packet using only two letters, one of them being "F".
For the antenna mounted inside the fuselage I used a self-manufactured aluminium ground plane of around 10"x8". For the externally mounted antenna I used the original aluminium ground plane which is about 1/4 of the size.
I would like to eventually return to having an out-of-sight solution but for the moment I have other priorities and am happy that at least the problem has been resolved, even if without any technical understanding.
For the antenna mounted inside the fuselage I used a self-manufactured aluminium ground plane of around 10"x8". For the externally mounted antenna I used the original aluminium ground plane which is about 1/4 of the size.
I would like to eventually return to having an out-of-sight solution but for the moment I have other priorities and am happy that at least the problem has been resolved, even if without any technical understanding.
