VHF/AIS antennas

[gettinthere]

successfully installed the Standard Horizon 2150 VHF/AIS radio.

Looking to upgrade the whip antenna at mast top. Shakespeare lists a new antenna that is optimized for AIS with additional bandwidth. Big deal? I don't see this with the other makers like Metz.

 

[Brian D]

Totally my opinion here...

An antenna is an antenna. I remember when marketers said digital television needed a special digital antenna. Bullocks! An antenna is an antenna. Now, some vertical antenna designs have better gain characteristics than others. Say a 5/8 wave compared to a 1/4 wave antenna. However, these characteristics will improve the ability of an antenna to 'hear' and 'talk' better, but saying that it is a specialized antenna for AIS is bullocks.

One could probably do just as well by putting up a 5/8 wave coat hanger on top of the mast as long as it is tuned to the frequency in use and the radio sees it as resonant.

Again, just my opinion and nothing more.

Now for the real stuff. Look at all the antennas you want to put on the mast head. Select the one that has the best plotted gain characteristics, not what the marketing folks say. Shakespeare may be a good manufacture, I don't know. I am used to Amateur radio manufactures who also provide commercial and military applications. I am not sure if Shakespeare does that. They may.

Find a couple of antennas you like and just do a comparison based on their specifications.

Allow me to add one more thing. You might also want to change out your coax cable and install fresh new connectors. Coax exhibits losses that increase over age. Especially if the ends of the coax are not properly weather sealed. However, if you think your coax is good then disregard.

 

[tkanzler]

From wikipedia:

"AIS transponders use two different frequencies, VHF maritime channels 87B (161.975 MHz) and 88B (162.025 MHz), and use 9.6 kbit/s Gaussian minimum shift keying (GMSK) modulation over 25 or 12.5 kHz channels using the High-level Data Link Control (HDLC) packet protocol."

So it's VHF on the high channels of the marine band. Sounds like a marine VHF antenna should be fine, though it's certainly possible there's more to it than that. I'm not an RF guy, but I'm not seeing where anything special has to be done for AIS.

 

[Don12364]

Brian D is right. VHF antennas are not finely tuned things like MF or other lower frequency antennas. The VHF band is only +/- 3 MHz wide on 159 MHz centre frequency (+/-1.9%) so the antenna's response will hardly vary across the band. It is best 'optimised', if that is possible, for CH16 because that might be where the ultimate performance would be required. They are only crudely 'tuned' by their length and any loading coil but seriously damped by the cable's impedance.
AIS easily achieves 10 miles ranges and has plenty of transmitter power and antenna height on ships - and anything more distant than 10 miles is of little interest anyway.
Anecdote:-
We had our AIS installed only a week before and were crossing the English Channel northwards almost on the Greenwich Meridian (0' 0" W or E?). On my AIS plotter screen I had 11 ships coming down the Dover Straight shipping lane directly at us. The viz was about 1 mile. I was up and down from nav table to cockpit like a madman, convinced of the great danger we must be in. My wife was at the helm. We actually only saw one ship and that altered course to go behind us. Once across the shipping lanes my wife remarked "That AIS thing is just something to frighten yourself with". Undeniably she was right --- as usual.

Now I have it set up NOT to show any ships further away than 10 miles (approx 24 minutes to collision). Plenty of time to decide what to do.
AIS sensitivities are not nearly as important as the emergency frequencies and will undoubtedly show the ship well before it becomes dangerous.

I tend to avoid buying from companies that are dishonest enough to try to sucker people into buying their products by extolling virtues that are either unnecessary or worse, counter to the common good.

 

[Richard19068]

With that setup you are just receiving AIS right? Do you feel like you are missing some AIS transmissions? I've had the same receiver for about a year and never thought I was missing anything with the same old antenna.

Just my thought.

 

[Deadhead]

AIS Antenna

FWIW - I installed a dedicated AIS antenna between the solar panels on my arch. (See pic) The service manager at my Beneteau dealer had told me that there might be interruptions in either the VHF or the AIS reception when using a splitter on the masthead VHF cable.

I don't remember if the antenna was Shakespeare's special AIS version, I tend to think it was not. I did use the LMR400 low loss coax cable.

I keep the AIS alarm on silent because it does get annoying.

DH