AIS 700 - VSWR fault

[MagicalArmchair]

I installed my new AIS 700 today and on powering it all up, it came up with an error: Antenna VSWR fault. As far as I know the VHF radio works perfectly well (new boat!), it certainly receives well. It used to have a Glomax FM splitter, however I have removed that as didn't want it left in as a point of failure. Through the Glomax previously, the FM radio received perfect clarity radio.

Despite the error with the new set up, the E7 still picks up AIS targets.

Do we think the aerial in kippered? Or perhaps replacing the plug would be a better start? I was going to get another aerial on the pushpit for the FM radio - could I use that as the aerial for the AIS and put the Glomax back in line with the VHFs aerial?

 

[GrahamD]

I would phone Raymarine technical department on Monday. I’ve always found them very helpful

 

[rszemeti]

Trying to diagnose antennae faults without a power/VSWR meter is like trying to diagnose battery problems without a test meter.

Your best bet would be to either purchase one cheaply on eBay or find someone with one. Simply attaching thVHF radio to the meter input and the aerial coax to the output and briefly pressing transmit will reveal whether there really is a problem ...

SWR POWER METER MOONRAKER SWR 270 100W DUAL BAND VHF UHF 120 500MHz | eBay

 

[Poey50]

Deja vu time for me. I had exactly the same symptoms after installing a new ariel and cable. The error screen looked identical to yours and it was a total puzzle. I contacted Salty John by phone who had sold me the kit. He diagnosed that a single strand of the outer cable was shorting. He said that this was still allowing the VHF and the AIS seemed to receive but without AIS function on transmit and probably a poor VHF transmit. And he was dead right. I think I disconnected both ariel plugs (meant climbing the mast) and then checking for continuity across outer sheath and inner core. Fortunately the short was in the bottom plug and it was soon fixed. Good luck!

 

[Daverw]

Most likely coax or plug fault, AIS does not normally need to be high up so easy to try an antenna on push pit, you will still have to sort out as although your VHF seems fine the high swr will reduce output power significantly and eventually damage your radio.

easy option would be to change plugs, testing with swr meter probably won’t tell you much new as the AIS is already telling you this.

As Poey50 says most problems are badly fitted plugs, with the outer shield badly fitted inside plug, inside I would use a crimped PL259 as this solves this

 

[MagicalArmchair]

Thank you all, has anyone tried one of these? I’m pushed for time before we deliver her, so any time saving is useful.

Shakespeare Wire Connector PL-259-CP-G

 

[Daverw]

I would not use it, I like to solder the centre pin, and the cost, well over the top. Get one from your nearest RadionHam shop, Martin Lynch, Moonraker, Nevada, many around, about£1.50

 

[MagicalArmchair]

I spoke to Hudson marine, and they had some interesting ideas (and were exceedingly helpful). At first they said it was most likely due to the antenna being on its way out and I could expect a trip up the mast, however, when he heard I was out of the water, he suggested it may be because the boat is not launched and thus the antenna is not grounded correctly. Does that sound feasible? Might the error go away when launched?

 

[Daverw]

Not likely as many boats today are not grounded anyway, antenna close to ground can have effect but it has the very close, Your mast would be enough of a ground plane

currently got my mast off, it’s laid flat on stands about 1.2m off floor, antenna on side and checked yesterday and SWR less than 1.2 across whole band, nothing else connected to mast, this is checked with antenna analyser rather than SWR meter

 

[Daverw]

Just a thought, do you have a deck connector? These can get water in and this would effect SWR as it changes impedance

 

[MagicalArmchair]

Mirage is in the water! I went down armed with plugs and solder, launched, turned on the AIS and lo and behold, the very high VSWR has gone away. Its now 1:4.1 - so not great, but not enough to anger the AIS700 and something that can wait for the boat to come back. So clearly launching did something good - onwards an upwards - thank you for the responses!

 

[MagicalArmchair]

When I went down again for a sail, the dreaded high VSWR error came up. I finished the install by fitting the GPS and tried again, but to no avail. I tried replacing the PL259, again, no luck.

The error goes away after first flagging, and it gives me targets and it reports my position. I figure this is probably safe enough to get me home and I can pop up the mast and replaced the VHF aerial once the season (whats left of it...) is over. Is there any risk to running the system with high VSWR? Or just go sailing and forget about it until fiddling time in winter?

 

[pvb]

AIS is a "nice to have", rather than a "life and death" feature. But your VHF transceiver is in the latter category, so you need to be sure that the antenna is OK.

 

[Daverw]

A high swr is not likely to cause any damage to the unit on receive, on transmit The power is low so short term i would expect to be ok, direct short would be a different matter. You could mute the transmit until you get it sorted.

 

[pvb]

A high swr is not likely to cause any damage to the unit on receive, on transmit The power is low so short term i would expect to be ok, direct short would be a different matter. You could mute the transmit until you get it sorted.

The antenna is shared with the VHF transceiver.

 

[Jamie Dundee]

25 watts through a compromised antenna could well fry the internals of your vhf. As PVB says you need to locate the problem. Your AIS box might have saved you the cost of a new vhf!

 

[Sea-Fever]

Yes, it needs sorting. A knackered antenna (which I think you have based on your description) will damage your VHF on transmit as the power is not being adequately radiated but reflected back into the radio.

 

[Poey50]

A solution that sorted out our similar sounding problem was provided to me by Salty John which I described in #4

You have to disconnect both ends of the cable then check for continuity between the the outer sheath and the inner which will mean climbing the mast for the disconnection. If you find continuity then the most likely culprit will be either of the two connectors. Hope that it is the lower one (it was on mine). It may just be a single strand of the outer cable shorting and may do so intermittently but that's enough.

 

[LadyInBed]

If it was ok for a bit after launching I would suggest a bad connection. The vibrations during the launch temperately cleaned up a connection.

 

[MagicalArmchair]

Thank you all. I've replaced (and checked for a short, there isn't one) the plug closest to the AIS unit. There is, on these Bavs, a deck plug as well I think - a union, so I'll check the plugs there too (water could have got in I suppose). Failing that, it's the first trip up the mast of Mirage . The good thing about her is she has an auxiliarily main halyard that runs through the mast, meaning I can use the spinny halyard as a backup line with my fall preventer on it. The VHF is an old Simrad RD68, so having a decent excuse to replace it wouldn't upset me greatly... it failing whilst on passage is a different matter.

I also have an emergency VHF aerial, and of course I always carry a hand held unit (which was helpful when on my old boat, the DSC filters failed ). I'll test with the emergency VHF aerial first, to make sure the diagnostics coming back from the AIS 700 are sound also.