JoCrow
New Member
Having just had AIS transceiver installed ( and supposedly checked), I find the message “VSWR level exceeded”. How can I check if this is antenna problem or wiring/connection or both please?
Antenna
- Thread starter JoCrow
- Start date
Jamie Dundee
Well-Known Member
Have you connected to a new dedicated antenna or used a splitter on the existing vhf? I have a distrust of splitters and always use a separate antenna.
JoCrow
New Member
Jamie,
Using a splitter
Using a splitter
MikeCC
Well-Known Member
Connect the AIS directly to antenna cable as first shot.
Check the PL-259 connectors have the centre conductor soldered into pin.
Although the AIS is already indicating a fault, you could get hold of an SWR meter and try it on VHF.
After that it's just a process of elimination. Eg if there's a join at the mast, run a good temporary cable from radio to mast. Depending on antenna model, connection at base might be suspect. Mast cable might be damaged either through age or halyard chafe.
Check the PL-259 connectors have the centre conductor soldered into pin.
Although the AIS is already indicating a fault, you could get hold of an SWR meter and try it on VHF.
After that it's just a process of elimination. Eg if there's a join at the mast, run a good temporary cable from radio to mast. Depending on antenna model, connection at base might be suspect. Mast cable might be damaged either through age or halyard chafe.
willbank
Active Member
Don’t mean to hijack the thread but I am getting surprisingly poor VHF reception with a new Garmin 315i with a small antenna (see pic)- what are people’s thoughts on the best marine powerboat antenna that can withstand 45 knot performance?
Rappey
Well-Known Member
That is a good question and one i intensively googled with lack of results. I concluded no one seems to have carried out a vhf antenna shootout or test so buying one is a gamble.
Im sure many vhf antenna are cheap but inflated prices to make it appear high end.
All vhf antenna seem to have the "boat" markup added as antennas for other communication devices at higher and lower frequencys are also a lot cheaper !
The type of VHF antenna you use with your AIS system can also have a big impact on AIS range. Most VHF antennas are optimally tuned around 155-156 MHz but AIS uses frequencies around 162 MHz. In some cases, a good VHF antenna might be substantially less tuned at even close adjacent frequencies.
I bought a shakespear ais antenna as far cheaper than using a splitter and better tuned for ais.
Jamie Dundee
Well-Known Member
I have two Simrad 2.4m antennas, one for vhf and the other for AIS. The 2w AIS transmission regularly pings the Marine Traffic receiver in Dalton in Furness, over 60 miles away.
William_H
Well-Known Member
An antenna in its simplest form is a length of conductor 1/4 wavelength long or around 15 inches. I bought 2 of these for club support boats 475mm Stainless Steel VHF Marine Antenna | Jaycar Electronics along with bases Universal Antenna Base | Jaycar Electronics. (I beleive Jaycar are in UK as well as oz)(2 oz dollars to the squid) The tricky part is that you need a ground plane to connect to the shield outer part of cable at the antenna base. This can be in the form of an ali mast for mast top or stern rail fro AIS antenna. In the case of my support boats there was a ss frame for a sun shelter. A ss sheet plate folded over to clamp onto the horizontal tubing with a hole in it for the antenna base. A quite chepa solution for an antenna.
I think the stern rail or similar antenna is best option giving spacing from main VHF antenna on a mobo and emergency antenna for a sail boat. I would never go for a splitter. ol'will
I think the stern rail or similar antenna is best option giving spacing from main VHF antenna on a mobo and emergency antenna for a sail boat. I would never go for a splitter. ol'will
Ian_Edwards
Well-Known Member
What's the difference in length between a standard 155-156 MHz and an AIS antenna at 162 MHz?
I have an old 155-156 MHz antenna and I'm wondering if i can re-purpose it to work with my AIS.
I currently have a splitter, but like many people I'm suspicious of it as a potential failure point.
A rough calculation shows that 1/4 wavelength at 156Mz is about 0.480m, and at 165Mhz it's 0.455m, a difference of 25mm.
Can I just shorten it 25mm?
Or is this too simplistic an approach?
I have an old 155-156 MHz antenna and I'm wondering if i can re-purpose it to work with my AIS.
I currently have a splitter, but like many people I'm suspicious of it as a potential failure point.
A rough calculation shows that 1/4 wavelength at 156Mz is about 0.480m, and at 165Mhz it's 0.455m, a difference of 25mm.
Can I just shorten it 25mm?
Or is this too simplistic an approach?
Rappey
Well-Known Member
Cb antennas used to have a screw in/out tip to fine tune the swr. 1mm can make a difference.
Cutting 25mm will work. From radio articles I've read 1/4 wave is not very effective but half wave can be better than full wave .
Coax is another consideration as many antenna come with moulded rg58 cable which is rubbish once you add the mast length as your losing over half you signal before you get to the antenna.
Cutting 25mm will work. From radio articles I've read 1/4 wave is not very effective but half wave can be better than full wave .
Coax is another consideration as many antenna come with moulded rg58 cable which is rubbish once you add the mast length as your losing over half you signal before you get to the antenna.
