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The Ubiquitous Mast Antenna Does What Exactly?

Ensenada Crab

Member I
Have been thinking of installing AIS, and maybe installing an AIS-specific antenna atop the mast. but when i started looking around the marina, every mast on every boat has a small antenna on it--including mine. so they aren't all for AIS, what are those small (2-3 foot) antennas for?
 

footrope

Contributing Partner
Blogs Author
They are for the ubiquitous marine VHF transceivers. Most of us have one onboard. Checkout West Marine's or Defender's website, or ICOM, Standard Horizon or your favorite boating supply store for examples. AIS receives and transmits over a couple of reserved marine VHF frequencies. Also check the Coast Guard regs for radio requirements for your size vessel.
 

fool

Member III
VHF most likely at topmast, that would give you the furthest reach for your "line-of-site" radio frequencies.

Rather than purchase a separate antennae you might consider an antennae splitter for AIS. I've added a SI-Tex Zero Loss splitter to mine and don't notice any conflict when using the same antennae for both purposes. Having AIS antennae at the masthead also allows for the furthest signal reach.

https://www.si-tex.com/item/metadataaiszerolossantennasplittermodule

There is this vague recollection that some data could be lost or incomplete with lesser splitters, so do your own due diligence should you go this route. I'm to lazy to recall or research what I've forgotten.

Regards,

Max
 

Teranodon

Member III
Sounds like you may not have a VHF radio for the masthead antenna. In that case, you might consider getting a Garmin VHF with built-in AIS receiver. This is what I did. It has a splitter in the unit, so you only need one antenna. The AIS output is via NMEA2000, displayable on many chartplotters. Just an idea.
 

Parrothead

Member III
+1 to what Max (fool) said. I have the same setup with a Quark receiver and a KJM splitter. Works great, no trip up the mast, no second cable, great altitude for reception. The Quark receiver sends signal wirelessly throughout the boat via Wifi and I have an iPad with iNavX for a display. No other network connections needed, completely local to the boat.
 

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Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
I have the Vesper splitter recommended by Vesper for their Watchmate unit (for a cool $250 more). Said to be important.

Also, AIS value enhanced by an antenna designed for both AIS and VHS. Mine is a basic antenna, but still sees ships well over 50 miles away when offshore.
 

bgary

Advanced Beginner
Blogs Author
^^^ what he said.

The important tidbit is that if you have two devices which require antennas, you don't want to have the antennas (antennae?) near each other. Having two in close proximity (on the same masthead, for example) is A Bad Idea - I don't understand the physics of it, but the short version is that a transmission from one will be grabbed by the other and can fry the associated electronics.

The splitters referenced above solve this problem elegantly - not just by allowing you to have a single masthead antenna shared by both VHF and AIS, but by electronically isolating them so the AIS is protected when the VHF is transmitting, and vice versa.

I assume that VHFs with built-in AIS do the same.

If you do go with a shared antenna, it's worth looking at the ones (e.g., Vesper's) that are designed to work for both frequency bands. A normal VHF antenna will work for AIS, but being designed for VHF frequencies, it won't also give you optimal AIS performance.

Bruce
 

tenders

Innocent Bystander
I have what Parrothead has, plus an $8 GPS antenna to feed the GPS signal that the Quark is capable of generating to my DSC-capable (but non-GPS) VHF radio. AIS via WiFi to iOS devices running iNavX, and my rough-duty Chrimebook running OpenCPN, is totally cool. I think the whole setup, not counting the VHF, iOS, and Chromebook devices, cost under $175.

It did take some futzing, but I may have futzed more than necessary since I rather enjoy electrical work.

Note that it IS POSSIBLE to connect an iOS device to the Quark WiFi signal for local AIS data, and still receive cellphone data when in range of shore stations. But it requires some adjustment to the network settings on the iOS device for the Quark WiFi station.
 
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