Antennas

[markejackson02]

Having some radio issues.  Searching the archives I see some people replaced their antennas to resolve problems.

Can an antenna go bad?  I have the original 7 shaped antenna. I am going to remove it, clean the bottom, create a new gasket, and clean all the connections.  It doesn't seem that the actual antenna which is buried in the plastic can go bad.

Am I incorrect?

[EricJ]

Other than corrosion, etc., antennas don't age out or wear out, so you're not incorrect.   That said, it's not unusual for the connectors to be a bit dirty or corroded, or for the antenna cables to have gotten kinked or pinched or chafed somewhere along the way.    

 

[Oscar Avalle]

Having some radio issues.  Searching the archives I see some people replaced their antennas to resolve problems.

Can an antenna go bad?  I have the original 7 shaped antenna. I am going to remove it, clean the bottom, create a new gasket, and clean all the connections.  It doesn't seem that the actual antenna which is buried in the plastic can go bad.

Am I incorrect?

I had some antenna issue too and in my case the splitter had gone bad... so check the connections from the antenna to the radios.

 

 

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[jasona900]

I had an issue with my GPS dropping lock on satellites... turned out the connection on the back of the radio worked its way loose.  

[jaylw314]

When I asked my A&P to change out the RG-58 for RG-400 on my KT-76, he said the old cable was apparently just hanging by a couple strands from the tray.  I imagine there is much more vibration in the panel than there is on the roof, so don't forget to check there.

[markejackson02]

Today's project is to remove the seats and get under the panel to remove, clean, and replace all the connections.  If that doesn't help, will remove the antennas, clean and replace.  If that fails, will try to run new cable.

Sure hope it's just the connectors. 

[Marauder]

32 minutes ago, markejackson02 said:

Today's project is to remove the seats and get under the panel to remove, clean, and replace all the connections.  If that doesn't help, will remove the antennas, clean and replace.  If that fails, will try to run new cable.

Sure hope it's just the connectors. 

Connectors can and will always be a problem -- including the construction of them. I have seen these issues firsthand. When I had my new RG-400 cables terminated by the avionics shop, they made up a connector that was bad. Of course, I questioned why they didn't test the cable after they terminated it. Gave me an explanation which as someone who works in the electronics industry knew was a CYA BS.

[markejackson02]

Well crap.  After giant mis-adventure removing the seats I got under there and all the connections to the radio are new.  I cleaned the connector to one antenna but was prevented from flying by a giant thunderstorm parked over the airport.  May try tonight.

Very frustrating.  The radio works well enough in the pattern but once I try to listen to departure, whose antenna is about 15 miles away, everything is very faint and I have to turn on the squelch.  I have de-activated every electric device one by one but that doesn't change anything.  Running just the #1 radio with everything else turned off didn't help.  Mag check didn't change anything.

Next step will be to remove, clean , and reinstall the back antenna to see if that helps. 

It happens on both radios which makes me suspect there is something awry electrically somewhere.

 

[Bartman]

I had the same problem you are describing so we replaced my front Seven antenna with a new CI-196 and replaced all cable with new RG-400 and it made no significant difference. Dual Magnet overhaul gave a small improvement. I just replaced the ignition harness and now have the best radio I have had in 10 years of ownership. 

[larryb]

Radios and antennas can be easily tested on the ground by a competent avionics shop. There should be no need for shotgun troubleshooting. Antenna and cable can be tested with an SWR meter. Radio can be bench checked with a service monitor. Outside interference, like the ignition harness mentioned, is more difficult.

[markejackson02]

13 hours ago, Bartman said:

I had the same problem you are describing so we replaced my front Seven antenna with a new CI-196 and replaced all cable with new RG-400 and it made no significant difference. Dual Magnet overhaul gave a small improvement. I just replaced the ignition harness and now have the best radio I have had in 10 years of ownership. 

I am going to check it for loose connections.  It was overhauled about 50 hours ago and a new harness installed.  Will check all the grounding straps as well.

[markejackson02]

I removed the rear antenna, cleaned it, made a new gasket, cleaned the coax/screws, and reinstalled it.  Huge difference.  I can hear KSGR tower from the ground at KAXH now.

Worst part was crawling into the tailcone in the heat inside a metal hangar.  It had to be 120 in there.

Now I have to figure out how to do the front antenna.

 

[Bartman]

22 minutes ago, markejackson02 said:

I removed the rear antenna, cleaned it, made a new gasket, cleaned the coax/screws, and reinstalled it.  Huge difference.  I can hear KSGR tower from the ground at KAXH now.

Worst part was crawling into the tailcone in the heat inside a metal hangar.  It had to be 120 in there.

Now I have to figure out how to do the front antenna.

 

I'm happy to see you had good results. You can see the rear antenna from the avionics/battery access door, but you are right it sure is tough to reach with my T-Rex arms. To get to the front it just takes a long time, but not hard to do. Remove the seats, dash, left and overhead interior panels. The antenna base is under one of the pieces of plastic air plenum and easily accessible. Get some new screws and countersunk dress washers from spruce for the interior trim and freshen it up for just a few bucks. 

[markejackson02]

I removed the front antenna.  Wow.  First, there was an entire container of plumbers putty put in around everything.  Second, the plenum seems to be nothing but a support for the two rolls of duct tape that were used to seal everything.  Finally got it all apart.

This is the coax connector.  There was some kind of pink film all over the antenna, AN3 screws, and gasket.  Anyone know what this is?

 

[Marauder]

I removed the front antenna.  Wow.  First, there was an entire container of plumbers putty put in around everything.  Second, the plenum seems to be nothing but a support for the two rolls of duct tape that were used to seal everything.  Finally got it all apart.
This is the coax connector.  There was some kind of pink film all over the antenna, AN3 screws, and gasket.  Anyone know what this is?
 

It’s probably electrical insulation putty. Like 3M’s Scotchfil putty. One thing you want to look at are the locations where those clamps are located. I found a LOT of wear on the coax cables where they were held by them.




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[Marauder]

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[Bartman]

I think the pink sealant is fuel tank sealer. Look at the cable under the clamps @Marauder circled. I'll be surprised if you don't tell us you replaced it with new.  

[markejackson02]

1 hour ago, Bartman said:

I think the pink sealant is fuel tank sealer. Look at the cable under the clamps @Marauder circled. I'll be surprised if you don't tell us you replaced it with new.  

Did you reuse the clamps?

[Marauder]

Did you reuse the clamps?

I didn’t. I used tie wraps that were offset (one holding the cable and attached to other holding the structure). Those clamps have some sharp edges on them.






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[carusoam]

Looks like somebody got really serious about insulating the cabin from any chill entering...

-a-

[markejackson02]

8 hours ago, carusoam said:

Looks like somebody got really serious about insulating the cabin from any chill entering...

-a-

Yeah the entire cabin has 1/2" foam insulation.  Very useful in South Texas.

At least all the steel tubing looked to be in great shape.

[markejackson02]

Part of the issue might have orginiated when the plane was painted.  Apparently they didn't put new sealant around the antenna base.

Who votes for pro-seal and who votes for RTV Silicone for sealing the antenna base?

[Bartman]

My new CI-196 came with a new silicone or rubber gasket. On the surface area of the aircraft skin I cleaned and applied Alodine. I used the new gasket without a sealer directly on it. Since the aircraft paint and antenna paint are almost identical I ran a bead of white silicone around the edge. It looks great and sealed well. 

[EricJ]

What type of sealant is usually used around the perimeter of the antenna base?  RTV?   My 7 antennas are both dried up with a fair number of gaps, etc., and need some attention.   I'm wondering what is used on those typically.

 

[jetdriven]

PRC type fuel tank glue. CS3204 works great.  Silicone is a nightmare. When the plane is repainted, some 20 years later even, the silicone cant be painted. then they charge extra to remove the antennas to get it off.  before then it getd mildewy or degrades. either way, it doesnt belong on an aircraft.

load a small syringe with 10cc of the stuff, then  apply it to the perimeter of the antenna base just inside the edge.  then tighten down and smear with wet finger.