UV damage to VRC-12 antennas AS-3900, 1729, etc.

[OPCOM]

There have been posts from users of the the AS-3900/VRC Antenna - Similar to the AS-1729/VRC and others that go with the VRC-12 radio sets:

The top section of the base (from what the spring sits on down to the mounting flange) is made of a plastic material such as acrylic. It is important to keep it covered with paint to prevent damage by UV radiation from the sun. There have been a few reports of the 1729 and 3900 bases failing at times, cracking off and leaving the whip and spring in the dust. Maybe these were units that had damaged paint and had become crazed by the UV until they snapped off during some rough driving. There is no more detail.

This was brought to mind because I saw one of the NG's hummers today, and the AS-3900 base's cylinder on one side was completely shed of CARC. I mentioned it to the soldiers that had been mudding it, and they seemed to take interest, hope they at least spray paint it. Hate for it to go bad on them at a critical time, these guys have been going to and from Iraq lately.

The wall of the cylinder seemed to be thinner on the 3900 compared to what I remember of the 1729 but it could be my perception or a figment of my imagination, having only seen them from the outside, trying to see inside to view the guts. I don't consider the perception of wall thickness an issue at all, I'd gladly have either one.

While peering into the windows to get a look at the radio mounts, I noticed inside the vehicle, a brown painted wooden ammo box about 18" on a side and 7" tall, mounted right between the dirver and co-driver seats. The 6" speaker grilles on each side made it look suspiciously like an up-armored car stereo. I didn't ask about it.

And indeed they had been mudding, apparently the hummer and a van of troops, taking turns practicing driving it on sloppy surfaces.

 

[emmado22]

All the 3900's and 3900A's I've seen were made of metal.. Some 1729's are made of plastic.....

I've also never seen a broken base as you describe. I've seen the WHOLE mount and abse sheared off from the vehicle, but never the base in pieces.. I wonder what sort of extreme off road driving they do......

 

[OPCOM]

well, I seen through the clear-ish plastic base on the 3900 on that hummer for myself. I made a mistake above and posted "1729" instead of "3684".

The base underneath where the cable goes was metal, but the top part was plastic and supported the metal top plate and spring like my AS-3684 (which I did repaint). Maybe there are several kinds of them depending on the contractor. No telling about the driving, my brother told me about a couple busted ones he saw in iraq, but I suppose they could have been shot off by lucky shots? Heck if I know, only he says he was told the sunlight crazes and weakens them after a few years if the paint gets rubbed or scraped off and then they can crack and break. He also said that some soldeirs had a bad habit of hanging some of their crap from the otherwise stout-looking base. Maybe someone was pulling his leg or he was telling me stories, but I think I can believe the UV risk part of it becaue it does look like lexan / acrylic / plexiglass type plastic.

Again I did not mean I had a AS-1729 with plastic parts, but instead I have the AS-3684 which in my specimen does have plastic, so sorry for the error.

 

[OPCOM]

Here while looking for a picture to explain what I meant, I did find a nice PDF about the AS-1729 (attach), but anyway the pic below shows what the plastic top "cylinder body" part I'm speaking of is on the 3684 and 3900. There are several 3900 on the place for $20, I should get one to open it up and discover the secrets....

 

[cranetruck]

Patrick, scraped some paint off the housing and can confirm that the upper portion is plastic (Polycarbonate/Lexan?) and the lower part is aluminum.

 

[lindyp38]

is there a cover for this base....when the antenna is off?

 

[sigo]

There is a plastic cover for the top that covers the threads and contact where the radiating element screws on to the base but I don't think there is a cover for the whole base. At least in 12 years of Army signal work I've never seen one. It's not in any of the common TM's either. Not to say it's not out there, but it sure isn't common if it is.

With that said I have seen some bases fail, I've seen some of the plastic parts cracked and brittle probably in imminent danger of failing and I've seen the springs and elements fail.... but not many. Even in theater provided equipment (the gear that gets rode HARD and put away wet for multiple tours) the complete failures are somewhat uncommon.

What is common are radio systems that don't work as well as they should. Reduced range, power failures, bad audio, and reduced range. They problems are many but it all comes down to proper maintenance. A failure doesn't have to be a cracked or sheared off base, it can be much less catastrophic and still impact the mission. Cracked elements, corroded contacts between elements, or between bottom element and base, water inside the antenna base, corrosion between the RF cable and base, abraded cables, bad grounding, dirt, corrosion, improper installation, operator headspace, etc, etc, etc... With proper and regular maintenance the systems last longer and work better. With a knowledgeable and conscientious operator and/or maintainer problems are found before they reach the point of complete physical failure. Too often that doesn't happen. Fortunately, other problems rear their heads prior to complete physical failure of components so component replacement is prompted before it gets too bad. </commo maintenance rant>

 

[KsM715]

sigo, I hear you load and clear, especially when it comes to operator headspace ect. I did 7 years in the USAF as Ground Comm, Radio Maint. In those 7 years I never saw any sort of cover for those bases. Other than the plastic cap that you can see in cranetrucks pic above.



Now if someone had some extra canvas lying around and was good with a sewing machine.......................

 

[NEIOWA]

That's why Sam pays Co Commo NCO. To run around with a can/bottle of paint and a pencil eraser.