AIS Antenna Troubleshooting - Poor VSWR possible causes?

[hpeer]

I have seen an AIS throw a VSWR alarm if something metallic has been moved too close to the antenna.

Not likely, but thought worth a mention.

[AndyBC]

FWIW - I don't know anything about VSWR, and after reading this thread it appears I have the crappy screw-on connectors (one at the top of the mast, one at the AIS unit, and one at the VHF). My emtrak B954 AIS works great for my purposes (15-20 nm range) and the VHF is clear (I use the shakespeare 5215 AIS/VHF antenna). Maybe one day I will test the VSWR.

[Jammer]

Originally Posted by AndyBC

FWIW - I don't know anything about VSWR, and after reading this thread it appears I have the crappy screw-on connectors (one at the top of the mast, one at the AIS unit, and one at the VHF). My emtrak B954 AIS works great for my purposes (15-20 nm range) and the VHF is clear (I use the shakespeare 5215 AIS/VHF antenna). Maybe one day I will test the VSWR.

They usually work for a while, especially in fresh water. You can attach a connector with electrical tape and get it to work for a while. The trick is getting it to work reliably over time in a salt environment.

[Tin Tin]

Try connecting your VHF radio antenna to the AIS and see if it makes a difference. If it improves considerably consider getting a splitter.

[deblen]

Originally Posted by AndyBC

FWIW - I don't know anything about VSWR, and after reading this thread it appears I have the crappy screw-on connectors (one at the top of the mast, one at the AIS unit, and one at the VHF). My emtrak B954 AIS works great for my purposes (15-20 nm range) and the VHF is clear (I use the shakespeare 5215 AIS/VHF antenna). Maybe one day I will test the VSWR.

15-20 NM using a 5215 is normal good performance,from my professional experience. Your VSWR is OK IMHO.


What may happen in future is rainwater intrusion up at the 5215 connector junction. Read my previous post about how to seal that junction with rubber tape & liquid tape.

Cheers/Len

[catalystcat]

[QUOTE=Tessellate;3917941]Thanks, sounds like I should suspect the connector first and foremost.

I have successfully soldered before (VHF connections) but this time I guess I didn't do a great job. It worked for 2 months though (a Shakespeare PL-259-G). Upon disassembly the solder fell off the braid. So I didn't get enough solder into the braid holes, or didn't get the connector hot enough. I've watched many Youtube videos plus marinehowto.com's guide on antenna connectors. But I typically borrow a soldering iron from a neighboring boat, and the one I borrowed wasn't very good (dirty tip, not cleaned in a long time probably) and I was working in a cramped space in the aft berth.

[deblen]

[QUOTE=catalystcat;3918193]

Originally Posted by Tessellate

Thanks, sounds like I should suspect the connector first and foremost.

I have successfully soldered before (VHF connections) but this time I guess I didn't do a great job. It worked for 2 months though (a Shakespeare PL-259-G). Upon disassembly the solder fell off the braid. So I didn't get enough solder into the braid holes, or didn't get the connector hot enough. I've watched many Youtube videos plus marinehowto.com's guide on antenna connectors. But I typically borrow a soldering iron from a neighboring boat, and the one I borrowed wasn't very good (dirty tip, not cleaned in a long time probably) and I was working in a cramped space in the aft berth.

Soldering the braid to a PL259 shell is no easy feat-especially for an occasional DIYer. Most attempts will end like yours-not enough heat on the shell/not powerful enough iron.
It is equally easy to overheat the shell and melt/distort the insulator,degrading the finished VSWR.


That is why I suggest that DIYers do not solder PL259s. Read my prev.post for a method that works well.
Cheers/Len

[catalystcat]

[QUOTE=Tessellate;3917941]

I have successfully soldered before (VHF connections) but this time I guess I didn't do a great job. It worked for 2 months though (a Shakespeare PL-259-G). Upon disassembly the solder fell off the braid. So I didn't get enough solder into the braid holes, or didn't get the connector hot enough. I've watched many Youtube videos plus marinehowto.com's guide on antenna connectors. But I typically borrow a soldering iron from a neighboring boat, and the one I borrowed wasn't very good (dirty tip, not cleaned in a long time probably) and I was working in a cramped space in the aft berth.


If the solder fell off the braid, you probably had a cold solder joint. Just enough connection to give a brief impression that you had a real connection.

A suggestion is to get someone who is really good at soldering to get the solder to give good wetting on the braid.

Absent that, fix up the soldering iron a little bit - get the iron hot, apply some flux or use a rosin core solder, scrub the tip a bit (something as simple as a wet rag can do this), repeat until the solder melts and wets the tip so that it is shiny.

Then, clean up the braid and the mating surface however you can - e.g., buffing with something like an eraser or even a very mild sandpaper - and wipe clean.

You need to get the braid hot enough to melt the solder. So, while you are getting it hot, you can hopefully find something to protect the cable polymer from melting too much (e.g., small metal shield/foil/high temp ceramic/whatever, since this is too small for a soldering cloth from the hardware store). Of course, a higher powered soldering tool/iron with just the right size tip can make a world of difference.

Sometimes people try to get the surfaces pre-wet with solder. However, you might want to do this if the previous steps fail to get a good joint, because the more you reheat solder, the less friendly it gets. But, if you are having trouble, it can be a decent option.


You know you have a decent connection if the solder joint edges slope smoothly into the surfaces, kinda like a smooth ramp. If they look like a raindrop on a surface with an abrupt angle, you have a cold solder joint.

[catalystcat]

A couple of other things -

Does the SWR stay high at all frequencies? (4.4 is very high. 2 is considered marginal; I consider 1.5 to be kinda high) If so, the nearby interference is probably not the culprit.

The cleaning process I note above is done with a hot tip.

[Tessellate]

Originally Posted by S/V Illusion

What seems confusing is that he said he replaced the coax connector 3 times.

Yes, the *inside* coax connection that connects to the AIS unit. Some antennas have an external coax connector and an internal, and in that case those antennas have two connectors. The Shakespeare 5250-AIS antenna has no external connector because the wire is integral to the antenna. I snaked the bare wire by lead line (used the previous antenna's coax cable actually) through a deck cable clam into the stern and then attach the internal connector in place, to plug in to the AIS unit.

In contrast, our masthead VHF antenna has an external and internal connector. Probably for convenience so you can replace or remove the antenna without cutting the coax and reterminating with a coupler while up the mast.

[Jammer]

Originally Posted by Tessellate

In contrast, our masthead VHF antenna has an external and internal connector. Probably for convenience so you can replace or remove the antenna without cutting the coax and reterminating with a coupler while up the mast.

It also makes it possible to troubleshoot the antenna and the feedline as separate assemblies using any of a variety of techniques. And, it makes it possible to replace a failed feedline without replacing the antenna.


The Shakespeare 5215-AIS is the equivalent to what you have except with its own connector (what you're calling an "external" connector) and with a different mounting base.

[abarrow]

This is why I bought a resistive VHF dummy load. A 25 watt version isn't expensive, and it'll help you isolate the coax or the antenna. Just replace your antenna with the dummy load at the end of the coax and test VSWR. If it's still high, it's your coax/connectors. With so many connector replacements, are you confident that your coax hasn't been damaged?

If you don't want to spring for a purpose-built dummy load, get a 5 watt 50 ohm resistor (NOT WIREWOUND) and solder it into a PL-259 connector. Test it on the back of your SWR meter first to ensure it's okay, then take it to the top of the mast and put it on your coax.

[VoyagerCT]

While a VSWR is purely an RF characteristic of marine cables, you may be surprised to know that DC connectivity is also important.
Some equipment provides DC power via the cable (e.g: power boosters, etc), but more importantly, lack of DC connectivity could indicate an internally broken wire. This will affect the RF impedance significantly, thus your VSWR.
Breaks can result from a tight bend in the cable, a defective cable, or a poor connection at either end.
Good luck with your AIS. “Don’t leave home (port) without it!”

_____________
Voyager CT

[dreuge]

Test using the main VHF antenna. If all works then replace the AIS antenna and feed line cable.

[abarrow]

Originally Posted by VoyagerCT

While a VSWR is purely an RF characteristic of marine cables, you may be surprised to know that DC connectivity is also important.
Some equipment provides DC power via the cable (e.g: power boosters, etc), but more importantly, lack of DC connectivity could indicate an internally broken wire. This will affect the RF impedance significantly, thus your VSWR.
Breaks can result from a tight bend in the cable, a defective cable, or a poor connection at either end.
Good luck with your AIS. “Don’t leave home (port) without it!”

_____________
Voyager CT

If there is a break in either the shield or the center conductor, all power will be reflected at that point, and will show nearly 100% VSWR.