AIS VSWR troubleshooting help please!

[Silverfox]

I have a VSWR problem and am trying to find the cause without access to an SWR meter. I am an amateur when it comes to electronics and would really appreciate some advice.

I will try and be logical and provide information on the kit involved first and secondly what I have found so far....

My set up is all Raymarine comprising:-
e7 Chartplotter/MFD
AIS650 transponder
AIS100
Masthead Vtronix Hawk VHF antenna and approx 60ft cable (this was bought as a package 10 years ago.) mounted on top of 45ft mast

Symptoms of the problem are.....

Not seeing AIS traffic until it's about 3 miles away, with some exceptions where I see up to 8 miles
losing and refinding AIS targets
Occasional VWSR errors flagged up on the Chartplotter

Troubleshooting so far...

Updated software on Chartplotter and AIS650 today using the latest versions on the Raymarine website
Refastened all connectors to AIS550/splitter/VHF
I then connected my laptop to the AIS650 and ran ProAIS2.

All diagnostics are OK except the VSWR is showing at 5.1:1 which I know is well outside the recommended range of 1:1 - 2.5:1. So, I then connected the antenna cable direct to the AIS650 (missing out the splitter) and the VSWR was worse and now varied from 7.5:1 - 8.5:1.

From this, I concluded that the problem was either the antenna/cable or the AIS650. Given that it will cost me around £80 to replace an old antenna and cable, I plan to replace this and retest if I still have a problem then it must be the AIS650 which would need to go back to Raymarine or an agent for repair.

So my questions, to those who really understand these things, is "have I got it right so far and am I missing something that I can do to isolate the problem further ?" all suggestions welcome and gratefully received.

[Brian.D]

The problem may be as simple as the connectors. One way to fine out is to try and twist the connector. Not very hard twist, but hard enough to see if the connector moves. It shouldn't.

Also, when doing the SWR test, wiggle the cable where ever there is a connection or junction such as on the splitter.

High SWR is usually synonymous with poor connections, unless the antenna has gone bad. That is why the twist test will help determine if the shield of the cable is still sound. You may have to go up the mast and do the same. But, if you go up, replace the connector and ensure that the cable is good. If by chance you do a twist test and the connector actually rotates then your shield is faulty. You will need to cut that connector off and put on a new one.

JMHO

[smac999]

If you have a spare antenna around. Plug it in and stick on deck. And see what happens. It it works then it’s the existing antenna or cable. You should have a spare one on board in case the mast one, or the mast itself. Ever breaks

Like a Shakespeare 5911

To determine if it’s the current antenna or cable. You ether need another antenna or a dummy load to put up top on existing cable. . Or temporary cable run to existing antenna. And see which one works and which does not.

Or just change both.

There may be connections at base of mast to check as well.

[S/V Illusion]

The word “occasional” you used to describe the problem implies a bad coax connector which would exhibit itself in variations of SWR so the other comments are likely correct. Start with the close ones but it’s usually the one farthest up the mast most exposed to weather.

[Silverfox]

Guys, A really big thanks. I now have a clear way forwards.

[Midnight Son]

I had a similar issue, years ago, with SSB, humidity/water intrusion at antenna coupling. Had words with installer (company electrician, not a radio tech.) about proper coupling.
Cheers

[StoneCrab]

Is it common to coat the connectors with silicone?
Would that help prevent corrosion?

[Cpt Pat]

Originally Posted by Brian.D

The problem may be as simple as the connectors. One way to fine out is to try and twist the connector. Not very hard twist, but hard enough to see if the connector moves. It shouldn't.

Also, when doing the SWR test, wiggle the cable where ever there is a connection or junction such as on the splitter.

High SWR is usually synonymous with poor connections, unless the antenna has gone bad. That is why the twist test will help determine if the shield of the cable is still sound. You may have to go up the mast and do the same. But, if you go up, replace the connector and ensure that the cable is good. If by chance you do a twist test and the connector actually rotates then your shield is faulty. You will need to cut that connector off and put on a new one.

JMHO

Agree with above. It's probably a bad connector. If you used one of those "solderless" PL-259 connectors -- it is almost certainly the connectors. Solderless PL-259s are garbage! And on a boat, in a corrosive atmosphere (salt air) they are a completely worthless. Twisting the connectors makes me cringe, but it is a way to determine if the connector is junk -- solderless connectors can be twisted. After twisting, it may work for a week, only a millisecond, or not at all. Get rid of any solderless PL-259 connectors, learn to solder PL-259s, or find someone who can. YouTube has videos.

If you want to confirm the AIS transponder is not the cause (which is very unlikely), connect a 50 ohm dummy load. Here's one: https://www.hamradio.com/detail.cfm?pid=H0-009261. Or you can just solder a 47 ohm 1 watt resistor to a PL-259 connector (1 watt is adequate because the AIS transmitter duty cycle is very low). Use a higher wattage resistor if it makes you feel good.

[Cpt Pat]

Originally Posted by StoneCrab

Is it common to coat the connectors with silicone?
Would that help prevent corrosion?

I use 3M model 2229 mastic tape. It lasts for many years. Available at most hardware stores.

https://www.amazon.com/3M-Scotch-Sea...55204898&psc=1

PL-259 connectors are not waterproof. They MUST be sealed when exposed to weather.

I pity the poor skipper who uses a solderless connector at the top of his mast, and then fails to seal it from weather. He's double cursed and will get lots of exercise going up and down the mast. Mistakes like that give electronics at sea the bad reputation it has.

[StoneCrab]

Originally Posted by Cpt Pat

If you want to confirm the AIS transponder is not the cause (which is very unlikely), connect a 50 ohm dummy load.

OK I know that this is COMPLETELY obvious to anyone who has done this check, but what exactly are you doing with the dummy load which proves whether the AIS is or is not the cause?

My deep research at Google University explains that you are putting the dummy load in place of the antenna cable.... for adjusting and testing of the transceiver. Are there any adjustments to be done at an AIS or VHF transceiver? I understand using the SWR meter and tuning the antenna but I don't understand the dummy load application. If it is bad what do you see? Is this a go/no-go test?

[Brian.D]

Originally Posted by StoneCrab

OK I know that this is COMPLETELY obvious to anyone who has done this check, but what exactly are you doing with the dummy load which proves whether the AIS is or is not the cause?

My deep research at Google University explains that you are putting the dummy load in place of the antenna cable.... for adjusting and testing of the transceiver. Are there any adjustments to be done at an AIS or VHF transceiver? I understand using the SWR meter and tuning the antenna but I don't understand the dummy load application. If it is bad what do you see? Is this a go/no-go test?

For the purpose of trying to determine if the AIS box is faulty, then this dummy load would show up as a SWR higher than what is expected. Since the AIS radio has an output impedance of 50Ω and the antenna is expected to be 50Ω it would produce a SWR of 1:1. If the SWR shows, say 3:1, then the impedance mismatch would be 50Ω:150Ω. This would indicate that the radio's output amplifier is faulty.

Unless one is certified by the FCC to do repairs on marine radios, then no, there is nothing the user can do to make this work as advertised. It must be returned to an authorized repair center, sold on EBay (as is for parts), or stored in a circular bin.

[StoneCrab]

Thanks Brian for your explanation.

To finish the thought, is there a SWR meter between the 50 ohm dummy load and the radio or are you counting on the radio having a SWR meter built into it? I ask because my radios do not have an SWR meter.

... its a learning moment for me...

[Cpt Pat]

Originally Posted by StoneCrab

Thanks Brian for your explanation.

To finish the thought, is there a SWR meter between the 50 ohm dummy load and the radio or are you counting on the radio having a SWR meter built into it? I ask because my radios do not have an SWR meter.

... its a learning moment for me...

Every AIS transponder I've seen has some method for reading antenna SWR.

[Brian.D]

If testing a radio for power, one would put a power meter between the radio and the dummy load. Conversely if one is testing for the radio's accuracy if an internal SWR meter exist, then one would put a calibrated SWR meter between the radio and the dummy load. It is assumed (and rightly so) that the dummy load will match the impedance of the radio thus producing a SWR of 1:1. But you know what "assume" means. LOL

If the AIS radio is showing a 3:1 SWR in a dummy load, but the SWR meter between the radio and dummy load shows 1:1, then the AIS radio software or hardware controlling that function is faulty.

[Cpt Pat]

It's also useful to connect the dummy load to the antenna end of the cable and then measure SWR of the antenna itself. Even a cheap SWR and power meter, such as this one, will be very valuable for troubleshooting: https://www.gigaparts.com/mfj-822.ht...ABEgKEGfD_BwE#

To measure cable attenuation, place the SWR meter at the antenna end of the coax, terminating into the dummy load instead of the antenna. Then compare the power output at the radio into the dummy load to the power measured at the antenna end of the cable.

A 50 ohm dummy load is an important tool to simulate a "perfect antenna" so you can confirm/eliminate problems elsewhere.

Patrick
N8QH