Waterlogged MXTA-26 Antenna

[SteveShannon]

Last week I decided to put my dual band DB20G radio into my 4Runner instead of the one I keep dedicated to GMRS.  I have a Midland magnetic NMO mount on the roof with an MXTA26 antenna for use on GMRS. I already know the MXTA26 is worthless for 2 meters so I unscrewed the MXTA26 from the NMO mount where it has been.  Although i intended to use it for GMRS, the need simply never materialized and so for the past eight months or so the dedicated GMRS radio has been out of the 4Runner. The antenna has been in place without being disturbed for two years.

Apparently the seal for the NMO mount works really well, because even though it has been hot(ish) and very dry here for the past month, trapped water gushed out under the gasket at the base of the antenna as soon as I broke the seal. It was surprising. There was probably a tablespoon or two of water trapped in the base of the antenna.

My theory is that over the winters and rainy springs water travelled down the whip into the base.  I expected that there would be some kind of seal to prevent water from entering the cavities of the base, but if so it didn’t work. I have a second MXTA26 antenna that I mounted briefly but replaced with a Comet SBB5 that I can always use, but I’ll put the antenna analyzer on this one to see what it looks like.  I’ll compare the two, the nearly unused one vs. the one that was waterlogged.

So, because the much discussed format of this forum expects a question and allows us to vote the answers up or down, have any of you experienced this kind of water ingress with the Midland MXTA26 or another NMO mount antenna?

If so, do you just drain them and let them drip dry every so often?

[BoxCar]

6 hours ago, SteveShannon said:

The problem I experienced was caused by water coming in from the top of the antenna.  I’m guessing water ran down the whip, into the base.  Small amounts might also have entered via the set screw hole. Because the base seals tightly against the NMO mount, the water was able to build up. I think @WRXP381 has the right idea, to seal around the top of the base where the whip enters the shaft with some black RTV or silicone rubber. Although a person might be able to use grease there, the combined effects of wind and heat would eventually deplete that and dirt would stick to it.

I was just surprised that Midland didn’t have the socket for the whip sealed off from the base somehow.

A little blue lock-tite works wonders on the set screws. It usually stays liquid long enough to coat the entire set screw. I wonder if a little might "fix" your antenna problem. Squirt a little into the socket and let it dry before reinstalling the antenna and retuning it.

[gortex2]

I run LMR branded pepper shakers on UHF and 800/700 on my work trucks. I normally remove them monthly and even those at times have a small amount of moisture. I use the rubber washer under mine on my personal vehicles and have rarely seen the issue there. On my work truck I swap so much I normally use the ones built in.

 

[WRXP381]

Yes I have seen this on my mxta26 antenna after the first winter.  I found out in the summer when I took the antenna off for a car wash in the spring.   I fixed it with a very small amount of black rtv very carefully applied around the base of the whip.   I can’t see the fix and it worked perfectly.   I check now after every big rain and i re apply a small amount at the end of the summer.  No more water in the base of the antenna. 

[OffRoaderX]

Never had this occur on either Jeep, but even though we've driven through some heavy rainstorms its mostly hot and dry here.

[dosw]

My MXTA26 hasn't become waterlogged like that either. However, I found moisture in my MXTA25 once. But after giving it ample time to dry out it was fine.

 

I have gotten into the habit of using some diaelectric grease on the bottom o-ring and NMO threads of antennas. And I think I even put some into the whip hole of my antennas, to help prevent water intrusion.

 

Dielectric grease is non-conductive, but it also doesn't prevent connections from being made. And I've tested with the SWRsometer to verify that I didn't suddenly drive the SWR through the roof by applying the grease.

[SteveShannon]

2 hours ago, dosw said:

I have gotten into the habit of using some diaelectric grease on the bottom o-ring and NMO threads of antennas.

Since the base of the antenna contained water that escaped when I unscrewed it, that obviously wasn’t the problem, but I would recommend o-ring grease because it won’t attack the rubber o-ring. Perhaps dielectric grease is safe for o-rings but none of the qualities necessary for dielectric grease benefit an RF connection. 

[dosw]

2 hours ago, SteveShannon said:

Since the base of the antenna contained water that escaped when I unscrewed it, that obviously wasn’t the problem, but I would recommend o-ring grease because it won’t attack the rubber o-ring. Perhaps dielectric grease is safe for o-rings but none of the qualities necessary for dielectric grease benefit an RF connection. 

Serious question: is there a grease you would use to help prevent water intrusion? 

[BoxCar]

Vaseline has been used for years.

[SteveShannon]

7 hours ago, dosw said:

Serious question: is there a grease you would use to help prevent water intrusion? 

As @BoxCar said, Vaseline has been used for years, and for most modern o-rings it’s okay (same as dielectric grease), but plumbing shops sell a silicone grease specifically designed for lubricating o-rings and gaskets.  Soap can even be used.  But I’m not really convinced that any kind of grease should be used there anyways.  If the gasket or o-ring is in good shape and the surfaces of the mating parts on the base and mount are clean, using a dry o-ring might help to avoid the buildup of grit that might otherwise stick to grease.  Once the parts have been assembled they shouldn’t be moving against each other much like an o-ring against a hydraulic ram

The problem I experienced was caused by water coming in from the top of the antenna.  I’m guessing water ran down the whip, into the base.  Small amounts might also have entered via the set screw hole. Because the base seals tightly against the NMO mount, the water was able to build up. I think @WRXP381 has the right idea, to seal around the top of the base where the whip enters the shaft with some black RTV or silicone rubber. Although a person might be able to use grease there, the combined effects of wind and heat would eventually deplete that and dirt would stick to it.

I was just surprised that Midland didn’t have the socket for the whip sealed off from the base somehow.

[WRXB215]

@SteveShannon I used roofing caulk on my UT-72 around the edge of the rubber pad that goes between the roof and the base. I had seen where some people had a problem with water intrusion on that antenna and I didn't want to experience the same. I already had the roofing caulk and it is UV resistant. The antenna is black and the caulk is black so it didn't look bad. So far, so good.

[SteveShannon]

32 minutes ago, WRXB215 said:

@SteveShannon I used roofing caulk on my UT-72 around the edge of the rubber pad that goes between the roof and the base. I had seen where some people had a problem with water intrusion on that antenna and I didn't want to experience the same. I already had the roofing caulk and it is UV resistant. The antenna is black and the caulk is black so it didn't look bad. So far, so good.

I only have a mag mount, so my first thought is that you’re talking about the pad on the bottom of the mag mount.  Isn’t the rubber pad on the bottom of the mount, rather than the base of the antenna? I haven’t removed the rubber pad to see how the metal portion of the mount is constructed above the rubber pad. In any case having a better seal there certainly shouldn’t hurt.  It might keep grit from getting in there and possibly damaging your vehicle’s finish. A friend of mine bought a new truck and had a layer of protective film applied to the portion of the roof where the mag mount attaches.

[tcp2525]

On 8/14/2024 at 9:11 AM, SteveShannon said:

Last week I decided to put my dual band DB20G radio into my 4Runner instead of the one I keep dedicated to GMRS.  I have a Midland magnetic NMO mount on the roof with an MXTA26 antenna for use on GMRS. I already know the MXTA26 is worthless for 2 meters so I unscrewed the MXTA26 from the NMO mount where it has been.  Although i intended to use it for GMRS, the need simply never materialized and so for the past eight months or so the dedicated GMRS radio has been out of the 4Runner. The antenna has been in place without being disturbed for two years.

Apparently the seal for the NMO mount works really well, because even though it has been hot(ish) and very dry here for the past month, trapped water gushed out under the gasket at the base of the antenna as soon as I broke the seal. It was surprising. There was probably a tablespoon or two of water trapped in the base of the antenna.

My theory is that over the winters and rainy springs water travelled down the whip into the base.  I expected that there would be some kind of seal to prevent water from entering the cavities of the base, but if so it didn’t work. I have a second MXTA26 antenna that I mounted briefly but replaced with a Comet SBB5 that I can always use, but I’ll put the antenna analyzer on this one to see what it looks like.  I’ll compare the two, the nearly unused one vs. the one that was waterlogged.

So, because the much discussed format of this forum expects a question and allows us to vote the answers up or down, have any of you experienced this kind of water ingress with the Midland MXTA26 or another NMO mount antenna?

If so, do you just drain them and let them drip dry every so often?

Stick with a real quality antenna that is designed for the commercial environment or learn the hard way. If a company, Midland, can't even use stainless steel screws to hold the whip in you know you got a piece of crap. I posted about rusting set screws after having the antenna for three months. I won't be buying anymore overpriced and overrated Midland products. Toss that piece of crap and chock it up to a lesson learned. 

[SteveShannon]

2 minutes ago, tcp2525 said:

Stick with a real quality antenna that is designed for the commercial environment or learn the hard way. If a company, Midland, can't even use stainless steel screws to hold the whip in you know you got a piece of crap. I posted about rusting set screws after having the antenna for three months. I won't be buying anymore overpriced and overrated Midland products. Toss that piece of crap and chalk it up to a lesson learned. 

Well, that’s not going to happen.

[SteveShannon]

1 hour ago, BoxCar said:

A little blue lock-tite works wonders on the set screws. It usually stays liquid long enough to coat the entire set screw. I wonder if a little might "fix" your antenna problem. Squirt a little into the socket and let it dry before reinstalling the antenna and retuning it.

That’s a good idea.