Adding VHF/AIS antenna to the radar pole?

[GTom]

I have a pole mounted radar on the stern and planning to add a second antenna primarily for AIS but would also serve as a backup VHF aerial in case the mast decides to come down.

The pole is bog standard, looks like this:


Any ready-made brackets/arms on the market or it needs DIY? AFAIK the two antennas have to be at least 3' apart and the VHF/AIS above the lobe of the radar.***

Other question is the coax, can they run close to each other inside the pole without interference?

Also thinking on antennas: on the masthead I have a stainless whip. For the stern I might consider a fiberglass 1.2m/4' Glomex antenna.

***: this one seems like calling for some interference, which you only realize when carefully checking both Radar and AIS...:

[s/v Jedi]

I do not recommend that. Have you considered to use your masthead antenna with a good switch, like the one from Vesper, to connect both AIS transponder and VHF radio? This works great.

For backup, you can buy emergency antennas that you keep in a locker and connect when (only when) that time comes.

Try to minimize on installed gadgets that are exposed to the weather. Your radar pole is nice and clean, giving optimal performance as it is now

I know the Vesper switch costs money, but so do extra antennas and wicked mounts to get around the radar dome. You may even save some.

[a64pilot]

AIS antenna and GPS should not interfere, coax can be run together as it’s shielded. Radar and VHF should not interfere either.
The Vesper splitter actually improves VHF performance. There is no need to have separate antenna’s, and of course the higher the better.
I have the Vesper antenna that’s supposed to cover AIS and VHF frequencies, but I don’t think it’s necessary, I was replacing the antenna anyway as the mast was down.

Kato makes bolt on antenna arms, $120 ea I think
http://www.katomarine.com/radarwind-accessories.htm

[Jammer]

It is more common to use the backup antenna because of problems with the feedline and connectors than because of a dismasting. Food for thought.


For the pole mount, the makers of pole mounts have all kinds of options similar to the one in your photo. It is possible to extend any 1" mount VHF antenna vertically with spacers, available from Shakespeare and other antenna makers. 12" should be enough to get it out of the beam.



Fiberglass antennas have more windage but are good otherwise. Because they are sleeve dipole designs they should perform better in many cases, but the RF environment on a boat is complex enough that it is hard to demonstrate a meaningful improvement over a whip.


There are other mounting options for a secondary VHF. Spreaders, coach roof, taffrail, bimini or dodger. If you never fly a spinnaker then you can put them on the pulpit or maybe on a stanchion astern far enough that the genoa sheets don't hit it. There are also shorter antennas as small as 7" commercially available. These will not perform nearly as well on transmit but it may not matter that much for an antenna that is mainly used for AIS.


It's easy to overthink the VHF system. The splitters work great and in most cases will give you better overall performance at less cost than two separate antennas.

[Stewie12]

VHF is line of sight, so the higher the antenna the more range your radio will have.

[GTom]

Originally Posted by s/v Jedi

I do not recommend that. Have you considered to use your masthead antenna with a good switch, like the one from Vesper, to connect both AIS transponder and VHF radio? This works great.

I know they are far the cheapest and simplest but reluctant to use splitters. I like redundancy and using a splitter is introducing a possible point of failure disabling both your VHF and AIS at the same time, which can be frustrating when single handed/busy otherwise. A splitter also means some loss, which could degrade my weak class B AIS signal (less worried about the 25W VHF).

Originally Posted by a64pilot

AIS antenna and GPS should not interfere, coax can be run together as it’s shielded. Radar and VHF should not interfere either.
The Vesper splitter actually improves VHF performance. There is no need to have separate antenna’s, and of course the higher the better.
I have the Vesper antenna that’s supposed to cover AIS and VHF frequencies, but I don’t think it’s necessary, I was replacing the antenna anyway as the mast was down.

Kato makes bolt on antenna arms, $120 ea I think
Kato Marine

Thanks! regarding spacing, I went along the lines of the NMEA antenna spacing guidelines https://www.nmea.org/Assets/nmea%20a...ion%202011.pdf , I'll keep that 2' recommendation to be on the safe side.

Originally Posted by Stewie12

VHF is line of sight, so the higher the antenna the more range your radio will have.

With a good system we experienced VHF ducting very often. Also, AIS tend to benefit the phenomenon greatly. If your gear is low-loss, 30-40 miles range is not uncommon.

[boat driver]

Putting the mount on the radar mast is perfect- just be sure antenna is ten feet/3 meters above the water for line of sight of 2 watts transmit power. - and the stainless arms are easily obtained via west marine among other stores.
No interference in the mast with coax. check your antenna for heeling angles (db focus of antenna)

Without starting a debate, good seamanship, particularly offshore- is redundancy. The discussion of the splitter is ongoing, and in some cases the splitters are getting better, but then the shortfalls come into play. basically, splitters should be used as a last resort.
additionally the antenna tuning for VHF is channel 16, moving the tuning closer to AIS frequencies, particularity the weak AIS B, means compromise on both frequencies. Your call.


You already have knowledge of redundancy, and potential splitter damage burns both radios. Some of the cheaper splitters actually have a USCG record of poor quality.
Splitter VHF radios can not transmit during use/listening for an AIS Man Overboard Locating PLB transmitter. So if a man overboard occurs with locator the VHF radio prioritizes the splitter and antenna- meaning no VHF emergency calling may be done for risk of missing an incoming location signal.

Finally, line of sight is good- but with AIS B 2 watt the loss of cable length to masthead, splitter, connectors, and age of install add to loss that altitude does not assist. So as long a 2 watts at ten feet above water = 3 miles to earth surface- then that is optimized.
reception does not change dramatically- AIS A is 12 watts so far more punch- you will see them. THE GOAL IS you want them to see you. And if you only have 2watt transmit power of 3 miles- at ten feet- commercial antenna are generally 30-40 feet and up and so altitude on your part plays no real help past the power curve available. Remember- AIS is effective only if transmission and reception is calculated together.

[GTom]

Originally Posted by boat driver

Putting the mount on the radar mast is perfect- just be sure antenna is ten feet/3 meters above the water for line of sight of 2 watts transmit power. - and the stainless arms are easily obtained via west marine among other stores.
No interference in the mast with coax. check your antenna for heeling angles (db focus of antenna)

Without starting a debate, good seamanship, particularly offshore- is redundancy. The discussion of the splitter is ongoing, and in some cases the splitters are getting better, but then the shortfalls come into play. basically, splitters should be used as a last resort.
additionally the antenna tuning for VHF is channel 16, moving the tuning closer to AIS frequencies, particularity the weak AIS B, means compromise on both frequencies. Your call.


You already have knowledge of redundancy, and potential splitter damage burns both radios. Some of the cheaper splitters actually have a USCG record of poor quality.
Splitter VHF radios can not transmit during use/listening for an AIS Man Overboard Locating PLB transmitter. So if a man overboard occurs with locator the VHF radio prioritizes the splitter and antenna- meaning no VHF emergency calling may be done for risk of missing an incoming location signal.

Finally, line of sight is good- but with AIS B 2 watt the loss of cable length to masthead, splitter, connectors, and age of install add to loss that altitude does not assist. So as long a 2 watts at ten feet above water = 3 miles to earth surface- then that is optimized.
reception does not change dramatically- AIS A is 12 watts so far more punch- you will see them. THE GOAL IS you want them to see you. And if you only have 2watt transmit power of 3 miles- at ten feet- commercial antenna are generally 30-40 feet and up and so altitude on your part plays no real help past the power curve available. Remember- AIS is effective only if transmission and reception is calculated together.

The only thing that gives me second thoughts is wave height on open ocean. I don't have exact measures but ~3-4m above sea level is what I can do with the radar pole, this could easily be obscured even by a stronger swell. The rest is exactly my line of thinking, keeping losses at bay with a single, 9m long Ecoflex10 cable (got it from a never materialized wifi project) connected to an AIS tuned antenna.

[slug]

In life the best is always the most expensive

With ais the best is a separate ant mounted high up ... on a spreader ...serviced by a high quality. Coax cable

It would be a foolish mistake to unstep your mast for service and not fit a second ant


In the meantime a splitter is the best , compromised solution

[GTom]

Originally Posted by slug

In life the best is always the most expensive
With ais the best is a separate ant mounted high up ... on a spreader ...serviced by a high quality. Coax cable
It would be a foolish mistake to unstep your mast for service and not fit a second ant
In the meantime a splitter is the best , compromised solution

I reserve to have a ready infrastructure if the mast comes down, which means stern mounting, not even backstay. OTOH, if the boat rolls, survival chances of the radar pole are slim too but may be still better than the mast.

[s/v Jedi]

Originally Posted by GTom

I reserve to have a ready infrastructure if the mast comes down, which means stern mounting, not even backstay. OTOH, if the boat rolls, survival chances of the radar pole are slim too but may be still better than the mast.

The emergency antenna packed and ready in a cabinet at the navstation has by far the best chance of surviving a knock down, mast overboard or roll.

I’m with slug on this one, AIS on the spreader, VHF at masthead, emergency antenna safely stored just in case

[GTom]

Originally Posted by s/v Jedi

The emergency antenna packed and ready in a cabinet at the navstation has by far the best chance of surviving a knock down, mast overboard or roll.

I’m with slug on this one, AIS on the spreader, VHF at masthead, emergency antenna safely stored just in case

I'll check if I could squeeze two 10mm cables in the mast, afraid even one will be a challenge...

[s/v Jedi]

Originally Posted by GTom

I'll check if I could squeeze two 10mm cables in the mast, afraid even one will be a challenge...

Using an RG-8X up to the second spreader will perform better than RG-213 to a 10’ radar pole

[Cadence]

Originally Posted by s/v Jedi

The emergency antenna packed and ready in a cabinet at the navstation has by far the best chance of surviving a knock down, mast overboard or roll.

I’m with slug on this one, AIS on the spreader, VHF at masthead, emergency antenna safely stored just in case

Sound thinking. Nothing complex.

[Searles]

Simply glue or outher wise fasten an antenna plastic base mount to the top surface of the radar scanner ,run cable down with radar cable ,simple and easy