Waterproofing a Metz Manta antenna

[BogMonster]

The new RIB raider on the Vipermax does not seem to work properly - something wrong with the connection in the bottom I think as it does not seem to screw in properly (the first one got broken in the UK, that one screws right onto the coax fitting fine, but the replacement does not).

So I thought I would bite the bullet and get a Metz Manta as they seem to be well thought of.

Problem I have is that the bottom of the antenna is not waterproof for use on an A frame installation.

Photo of the antenna is here: http://www.saltyjohn.co.uk/metzmanta...ennaaerial.htm

The fat part of the base has an O ring (you can see it in the photo) so would seal onto the top of the plate on the A frame OK, but the fitting into the bottom is just a double ended SO259 connector which screws into a hole in the base of the antenna. Normally I use PTFE tape to waterproof threads but obviously that's no good on an antenna because it will insulate the connection ... likewise I'm not really keen on using sealant for the same reason.

Any thoughts on the best way to waterproof this properly? The plug onto the SO259 is no problem because I got a roll of the Bandit tape with the aerial so will wrap that up as directed, but it's not at all waterproof where it screws into the bottom of the antenna. The best idea I can come up with is to just squidge a load of silicone sealant around the base when assembling it onto the A frame but I'm not that convinced by that.

A separate problem is that the antenna is secured by a nut on the barrel of the SO259 connector. The antenna plate on the A frame is much thicker than the normal mounting bracket and in order to get the nut to engage on the threads I have to back the SO259 out so far there are only a couple of turns of thread still left in the antenna base, I haven't figured out how to sort this yet, what I really need is a double ended SO259 that is threaded all the way down the barrel but I haven't found one locally yet.

Does anybody see any problem with cutting the plug off the end of the RIB Raider antenna and using the same coax? I'd rather not run a new coax because it looks like being a PITA due to the amount of other stuff in the trunking...

[martini]

So the male 259 screws into the antenna as well as on to the plug? I' waiting for delivery of my Metz Manta at the mo, will be fitting it direct to the a-frame same as you So I guess I'll be asking myself the same questions soon.

I would probably just use a waterproof grease on the thread into the base of the antenna ie Tef-gel or similar, won't take much to fill the gaps in the thread making it moisture proof, even vaseline would prob do.

I'll have a better idea on mounting etc when I've got mine in front of me

[Hightower]

Check it all works first and then Sikaflex the whole connector. It's the only way to be sure it's protected. It'll also hold it all together and prevent the connector coming loose.

[jwalker]

Don't use silicon sealer around open electrical stuff or electronics. The sealers commonly use acetic acid and the vapour will be trapped withing the electrical stuff and cause corrosion. I'd be opening up the Vitronics piece of shit and doing a proper job of connecting the co-ax then resealing it. Use Sika or Tigerseal as Andy suggested for a permanent seal but be sure to clean the surface of the pvc co-ax outer cos it'll have traces of contamination on its surface to prevent sticktion of the Sika.

Personally I think it's crap that these marine components aren't given much more thought to their possible applications and fitments and designed accordingly. Having said that, I've got a shortish Pacific Arials antenna for my AIS which has lasted a good few years and still seems fine. It doesn't appear to be any better built that the rest but it's still there. I did dismantle it and do a proper sealing job when fitting it though. Just for info, internally it's a simple J antenna but, interestingly, the co-ax core is soldered to the impedence matching side and the screen it soldered to the feeder. Puzzled about that but it's receiving AIS info from 15 miles away so I doubt it's a mistake.

[jwalker]

Just looked at the Metz antenna, I wouldn't be buying that, the connector with eventually give you problems, the stainless whip doesn't appear tapered so it may stress out at the bottom and the typical application appears to be mast head and so not bumpy-thumpy as a rib is. Could be another 50kwid down the drain.

Why are you choosing the short type of antenna, have you a height restriction or is it a durability issue?

[martini]

Originally Posted by jwalker

Just looked at the Metz antenna, I wouldn't be buying that,

It's good enough to be spec'd on all USCG vessels and comes with a lifetime warranty

Wouldn't be my 1st choice for a primary vhf antenna though either I'd agree. I'm using an 8ft Comrod for my main vhf but using the Metz with my 2nd radio which is primarily for handling the AIS and as the emergency back up.

I don't think you'd get much water finding it's way vertically up from the underside of your a-frame and past all the threads. Even a squirt of that Wurth electrical contact spray would be enough to prevent corrosion inside the base.

If not send it back and get a new one

[BogMonster]

Originally Posted by martini

It's good enough to be spec'd on all USCG vessels and comes with a lifetime warranty

That was my thinking. The RIB raider on my old boat always worked really well, I think the threads in the base of this one have been cut wrong or something because the coax fitting goes into the old (broken) one fine and easily screws right in but the new one tightens up half way in - nothing visually obvious though.

I'm going to try and find a completely threaded double ended connector and then seal the antenna base onto the A frame, wrap up the plug and coax with the Bandit tape and then sealant over the top of that and around where it goes through the A frame, should be OK I think. Noted on the corrosion, thanks, hadn't thought of that. You can't buy Sikaflex here and all my tubes have dried out but I have some other waterproof (non silicone) clear sealant that I used to seal the radio etc in properly when I got the boat, so I'll use that.

There is a height restriction (low bridge) at one of the main launch sites so I'm just trying to keep it down.

[BogMonster]

Well I now know what I need - it's called a bulkhead connector, like this:

http://www.dxengineering.com/Parts.a...No=DXE-363-SST

whether I can find one anywhere around here may be a different matter...

[ashbypower]

Problem with that is that is is effectivley 2 connections and as a rule of thumb a connetion can loose 1db and affect VSWR if not done properly!!

[jwalker]

I think the lifetime warranty is a bonus to some folk but I feel they rely on inertia, after all and ignoring all the hassle of removing, returning and refitting, if the first one fails are you gonna want to rely on the replacement and hope it doesn't fail too?

Originally Posted by BogMonster

There is a height restriction (low bridge) at one of the main launch sites so I'm just trying to keep it down.

I asked because I use a different approach and have done this without failure for about fifteen years. I use a long high gain antenna on a nylon mount (not polythene or stainless). The nylon allows a bit of flexing to limit the flex load on the antenna base section but I mount the antenna base low enough so that it has a support arm further up the mast. The support needs to be non-metallic where it's close to the antenna. I've used two different methods of attaching the antenna to the support on each different installation, both very simple and worked fine, because I need to fold the antenna down each time after using my boat. The first setup used a rubber bonnet catch, the ones you'll be familiar with as car accessories, my present setup which has been in use for the past five years, is to use a couple of turns of double sided velcro around the antenna and a fixed stub of tube. You might imagine the velcro wouldn't hold but it does and the mast is two metres tall. The tube is slightly offset out of line with the base and has a short piece of thick walled rubber tube pushed on to it to give the neccessary stand-off from the antenna to prevent it effecting its performance. It's actually got other features and a bit more versatility than I've explained but that's for a different reason. And before the pedantic come along, I did check it out with an SWR meter during installation and it was spookily close to the antenna specification.

Here's a linky to what appears to me to be a mechanically well thought out design, the mount is wider at the base and tapering and the antenna element also wider at the base and tapering to reduce inertia loads. I'm not recommenting it because I haven't any experience of it but it would be where I put my money if I needed that type of product. All IMO of course.

[jwalker]

Originally Posted by ashbypower

Problem with that is that is is effectivley 2 connections and as a rule of thumb a connetion can loose 1db and affect VSWR if not done properly!!

Yeh I agree with that and even one connector is a connector too many in my book.

The RIB raider on my old boat always worked really well, I think the threads in the base of this one have been cut wrong or something because the coax fitting goes into the old (broken) one fine and easily screws right in but the new one tightens up half way in - nothing visually obvious though.

My point exactly, Vitronics shit.

[Chris]

Totally agree, Vitroniks are complete Shite.

The pacific aerial I have had on the back of TB for the last 2 years has been faultless.

There are no plugs to wire in to the aerial so no point of failure there. The cable is hard wired into the Nylon Base and the whip then screws into the base the actual antenna part is ony £22 so if you do snap it you can replace it really easily by just unscrewing the old one.

You will need to drag the new cable through from the Aframe upto the console, however the Pacific cables have this really neat and tidy fastfit plug on the end that screws into either a cable extension or the back of one of their PL259 plugs. The plug is really small so easy to drag through.

So no soldering and all the connectors are easy to water proof.

This is the set up I needed for TB. Marine Megastore seem to stock most of it.

P6182 Seamaster Pro VHF 1.0m UltraGlass Antenna
P6111 VHF/Cellular fold down mount with 5 meters of cable
P6018 VHF 5m Extension Cable
P1217 PL259 plug FastFit

The whole lot will set you back about £55 so not expensive and a much better option IMO.

[BogMonster]

Originally Posted by ashbypower

Problem with that is that is is effectivley 2 connections and as a rule of thumb a connetion can loose 1db and affect VSWR if not done properly!!

Well it is effectively exactly the same as what the antenna was supplied with (just that the thread on the supplied connector was not long enough) so I dont anticipate any difference in performance compared to the way it was supplied which was with a standard SO239/SO239 double ended connector.

Anyway the job is now done. What I did, for anybody else in the same situation, was:

1) Sourced an approx 2 inch long SO239 fully threaded bulkhead connector to replace the double ended SO239 that was supplied, so it would screw well into the base rather than just 2 or 3 threads. I screwed it in about 8-10 threads I think.

2) Chopped the funny Raider plug off and fitted a standard PL259 onto the end of the original VTronix coax (which was standard RG58 when I looked)

3) Cleaned upper and lower surfaces of the A frame mounting plate then applied a generous bead of sealant around the top of the hole and around where the connector goes into the antenna base, squidged the antenna down onto the hole which squeezed some sealant through the hole in the A frame and around the nut on the bottom - tightened the nut and then put a layer of sealant from the A frame mount covering over the nut and onto the threads so there should be no chance of water ingress into the bottom of the antenna.

4) Fitted the PL259 onto the bottom of the antenna, and then wrapped it all up with Bandit self amalgamating tape right down over the plug and onto the coax

5) to finish it off I smeared another good layer of the sealant over the top of the tape so the whole lot is continuously sealed right from the A frame down over the outside of the plug body and onto the coax

Should be pretty much submersible now. The sealant I used was something called Stixall which is a flexible clear adhesive sealant, it doesn't have the vinegar smell so I don't think it is based on acetic acid.

I tested it and it works well, radio check back to SWMBO's house had perfect audio (4 miles approx, but with a fairly big hill in the way) and listening to other traffic the signal strength is miles better. There was definitely a problem with the Vtronix, not sure what was wrong but it wasn't working properly and this is miles better

Time will tell if it lasts (the stainless mast is fairly stiff) but presumably the USCG give them a fairly hard time so hopefully it will be OK.

[Nos4r2]

The one I had on the SR4 was perfectly ok after 2 years of Sr4 abuse. That's probably more extreme use than most get.

[BogMonster]

Two slightly crap photos off my phone. Not all that pretty when you look underneath but I don't think the sea will get in

[martini]

Originally Posted by BogMonster

A separate problem is that the antenna is secured by a nut on the barrel of the SO259 connector. The antenna plate on the A frame is much thicker than the normal mounting bracket and in order to get the nut to engage on the threads I have to back the SO259 out so far there are only a couple of turns of thread still left in the antenna base, I haven't figured out how to sort this yet, what I really need is a double ended SO259 that is threaded all the way down the barrel but I haven't found one locally yet.

Got my Metz today, you're right the supplied SO259 is well too short, barely long enough for use with the supplied bracket, let alone when A-frame mounting. Just ordered one of those bulkhead SO259's that you linked to

[Salty John]

When we know the Metz is for use with a mounting other than the Metz bracket we supply a continuously threaded connector which replaces the connector in the base of the antenna. These continuously threaded PL258 connectors are readily available, but if you have any difficulty locating one don't hesitate to contact me and I'll send one.
The standard connector is fine for use with the Metz bracket.

[martini]

Originally Posted by Salty John

When we know the Metz is for use with a mounting other than the Metz bracket we supply a continuously threaded connector which replaces the connector in the base of the antenna. These continuously threaded PL258 connectors are readily available, but if you have any difficulty locating one don't hesitate to contact me and I'll send one.
The standard connector is fine for use with the Metz bracket.

Shame I didn't know to mention that but we live and learn!

Welcome to the forum John

[Channel Ribs]

Originally Posted by Salty John

... we supply a continuously threaded connector which replaces the connector in the base of the antenna.

That sounds promising, is there a pic of one on your site John?

[Salty John]

We don't sell these items because they are readily available at radio equipment suppliers. This one is at Rocket Radio, for instance:http://www.rocketradio.co.uk/pl258-l...pler-972-p.asp