7 Antenna

[jetdriven]

My rear one is behind that hat rack in the tail cone. Simply open the side cover and look up. 

[Bartman]

Thank you for the replies. I began removal of the interior today but only had about an hour to devote. Certainly is a job just to get the plastic off and I have a new respect for the avionics and maintenance guys out there. 

[Bartman]

I am glad I began this project, but not going to finish this as quickly as anticipated.  It does have the RG-58 and there are some clamps holding it to the steel roll cage and deformed exactly like @Marauder in post 5 this thread.  I can just barely see the end of a connection on the cable as it goes into the plenum and it does not look healthy itself so maybe there is or had been a leak but I have never seen any water ever.

The plenum is riveted thru the top and this is not a pleasant job so I ordered a new CI-196 antenna from Chief.  I called Chief and they do not have a gasket and cannot get from the manufacturer so sounds like it is a roll your own kinda deal so I'll discuss with the IA.  We have RG-400 and will run to both the new front and old rear antenna when I finish with the issue below.

The SB for window insulation had been completed way before my purchase 10 years ago.  I remember looking at it after the PPI, and I did not see any corrosion at that time.  It looks like they treated a couple of the steel tubes with a tan colored Rustoleum brush on paint and there is some surface corrosion bubbling through.  I took a Scotch Brite to the worst area and nothing bad so no major surgery needed.  I ordered green zinc chromate and will begin work soon under IA supervision.  Zinc chromate is reportedly highly toxic so I will use a mask and cover everything off including the panel and the rear.  Looks like emery cloth will be the tool of choice so plan to use a shop vac outside the plane with a long hose to eliminate dust.

This is NOT what I expected, but must be done.

 

[Marauder]

I am glad I began this project, but not going to finish this as quickly as anticipated.  It does have the RG-58 and there are some clamps holding it to the steel roll cage and deformed exactly like [mention=9886]Marauder[/mention] in post 5 this thread.  I can just barely see the end of a connection on the cable as it goes into the plenum and it does not look healthy itself so maybe there is or had been a leak but I have never seen any water ever.
The plenum is riveted thru the top and this is not a pleasant job so I ordered a new CI-196 antenna from Chief.  I called Chief and they do not have a gasket and cannot get from the manufacturer so sounds like it is a roll your own kinda deal so I'll discuss with the IA.  We have RG-400 and will run to both the new front and old rear antenna when I finish with the issue below.
The SB for window insulation had been completed way before my purchase 10 years ago.  I remember looking at it after the PPI, and I did not see any corrosion at that time.  It looks like they treated a couple of the steel tubes with a tan colored Rustoleum brush on paint and there is some surface corrosion bubbling through.  I took a Scotch Brite to the worst area and nothing bad so no major surgery needed.  I ordered green zinc chromate and will begin work soon under IA supervision.  Zinc chromate is reportedly highly toxic so I will use a mask and cover everything off including the panel and the rear.  Looks like emery cloth will be the tool of choice so plan to use a shop vac outside the plane with a long hose to eliminate dust.
This is NOT what I expected, but must be done.
 

Mine was riveted in place as well. It is not too tough to drill them out and replace them. Those clamps you mention were terrible! Ever point they were on a wire I found compression or actual damage to the wire. I was able to locate a flush tie wrap that sits more flush than the traditional tie wraps.

You’ll be happy with the results with the new RG-400.


Sent from my iPad using Tapatalk Pro

[Bartman]

After ordering and removal of the antenna I hit a snag. The antenna I ordered from Chief a week ago has not shipped yet, and my IA has been sick and didn't get the RG400 installed.  I would like to put it back on for a Memorial Day weekend adventure while hopefully the new CI-196 gets shipped soon, and I will not be using this antenna for navigation, just communications.  The old gasket looks like it was hatched with my bird and may have been reused, but I found current installation instructions on the Comant website here. https://www.cobham.com/media/5045/antennainstallationguide.pdf

As you can see in the pics below the old gasket completely isolated the antenna base from the aircraft skin and the only ground was thru the screws. I'm thinking of setting the old gasket aside and mount directly to the aircraft skin with washers to help it bite both surfaces and run some sealer around the edge after mounting. 

[jetdriven]

Put some PRC fuel tank sealer under the antenna along the perimeter. About a 1/8” to 3/16” bead. Tape the antenna and the fuselage first, Then put on PRC bolt it down then wipe the PRC wih a cloth rag wet with acetone.  Finish with a wet finger.  That’s what I did and it looks great and water is never getting under there again. 

[EricJ]

If it comes from the manufacturer with the gasket, I'd put the gasket in.  Sealing around the edge is probably still a good idea, even with the gasket.

The ground connections through the cable shell and the attachment bolts should be more than enough for electrical performance.   The aircraft skin will still provide a nice reflective ground plane even with the gasket in place.

Without the gasket there may be higher risk of corrosion and cracks.

[Bartman]

So as with many complaints I found more than one issue. Removal and cleaning of the antenna base seemed to make a difference so we decided on a weekend getaway. Along the route I decided to do a LOP mag check and it just so happened that center was giving someone an amendment to their route. Well as many expected as they read the last sentence I found that the noise and reception was immediately better when I switched to RIGHT mag only, but returned on BOTH and LEFT.  So I've got a 40 year load antenna and coax that will be replaced with RG 400 cable and a CI-196 blade antenna, and the single Dual mag will be sent for 500 hour service. 

I should have thought of this earlier. I did turn everything else in the plane off on previous flights including Bluetooth dongle, IPad, Stratus and everything in the panel and even pulled some circuit breakers. I knew about things such as condensers could cause noise and interference, but it just didn't occur to me to check the mags. Sounds like I have a bad condenser or something in the Magneto and I hope someone else learns something from this post.