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[N1AUP]

I know you get what you pay for, but I bought a Tram Discone antenna to use with my scanner.  It has not been working well, so I took it down to check things out.

I discovered that the part that supports the disk and the cone and keeps both insulated from each other was full of water. 

Any ideas on how to waterproof this particular antenna?

[WA3SKN]

Since the antenna jack is located inside the skirt, there should be no water egress.
However, I do know that GE Silicone bathtub caulk is a good insulator up through at least 440 MHz.  So a liberal coating in multiple areas might solve the problem.

-Mike.

[G4AON]

GE Silicone bathtub caulk is a good insulator up through at least 440 MHz.  So a liberal coating in multiple areas might solve the problem.

-Mike.

Beware that some domestic silicon sealants give off acetic acid when curing, this corrodes metal.

So called “liquid electrical tape”, which is rubber dissolved in solvents, is specifically made for waterproofing electrical items. The only downside is that it also dissolves rubber self amalgamating tape, hardly surprising given the solvents in the product.

73 Dave

[K5LXP]

Silicone II is ammonia, not acid based so is what's usually used for electrical/electronic applications.  As short of a time anything it touches would be exposed to a corrosive cure I wouldn't give using either one a 2nd thought to this application.  Careful what you ask for - if you don't seal it perfectly then the sealant can be even more effective at trapping moisture than if it weren't there at all.  One would assume that an antenna is designed to be outdoors (usually...) and that this could be caused by either a missing or failed part.  Reviewing what's there and discovering the cause of the water ingress might reveal a solution other than brute force gooping the thing up.  Little to lose either way you go though, at the end of the day it's a basic antenna.  Try something and see what happens.

Mark K5LXP
Albuquerque, NM

[WA3SKN]

It is not "acetic acid", it is methanol.
It has a resistance of nearly 10 Mega-ohms, both while wet and dry.  It does not corrode copper over time... or at least 42 years.  I have tested it.
It CAN hold in the water if not applied correctly.
Be aware SOME caulks use carbon in them and DO NOT WORK... resistance issues.
There is an RTV designed just for use with copper but does cost a lot more, I find the regular stuff cheaper and acceptable.

-Mike.

[SWMAN]

 Don’t mind if I go off topic a bit.

Do you think that type of silicone would be good to seal a toilet tank leaky bolt. The bolt is just a slight drip. If I dry it good will it seal ?  I hate to remove the entire tank and water supply for such a small leak. Besides, replacing those bolts is a major pain.
Thanks, Jim. W5JJG

[K5LXP]

The GE silicone webpage confirms Silicone I is acetic acid based.  The smell is unmistakable if you've ever worked in a darkroom around stop bath.  Silicone II claims better adhesion but I find shelf life is shorter.

As far as sealing a toilet tank, getting it really dry will be a trick.  Seems though if you can cover the screw head inside the tank it could work, millions of fish tanks can't be wrong.  For how long is the question but maybe long enough that something else will fail and you'll end up replacing the valve and seals all at once.

Mark K5LXP
Albuquerque, NM

[SWMAN]

 Thanks Mark for the info. If I do try this I will be installing the silicone to the inside of the tank. That seems logical as the water pressure will help the sealing process. But like you said getting it really dry may be challenging. I was thinking maybe epoxy mix putty may be better but that will be less flexible. Not sure.
Thanks again,  Jim. W5JJG

[N1AUP]

The disk sits on top of a black, plastic cylinder to physically support it, while keeping it electrically isolated from the cone.  A combination bolt / nut attaches the disk to the center pin of the SO239.  The cylinder lets water in from the joint adjacent to the disk, as well as the joint adjacent to the hub. 

I placed a coating of silicone 2 on both joints, reassembled the antenna, and then added a glob on top of the bolt.  Let it dry over night, then installed.

We will see if it holds up.

[WA3SKN]

There are now silicones and sealants that are specifically made for underwater use.  I would recommend checking into them first... they will cure underwater.
Any boating stores nearby?

-Mike.

[SWMAN]

 Mike,
 I don’t think that you can apply it underwater or can you ?

[WA3SKN]

That is what the instructions on the side of the tube said.  I have NOT tried it!

-Mike.