Can I use Shakespeare AS-2 as an AIS splitter?

[malbert73]

So my boat has 2 built in VHFs, and this splitter installed. Can I remove one of the VHFs and just let my Vesper AIS transponder/receiver connect instead?
Here's a picture of the device


I don't see a need for my current near coastal cruising to have 2 installed VHFs. I may keep one uninstalled as spare.

[continuouswave]

Originally Posted by malbert73

...my boat has 2 built in VHFs, and this [Shakespeare AS-2 automatic coaxial relay] installed. Can I remove one of the VHFs and just let my Vesper AIS transponder/receiver connect instead?

According to the manufacturer, the Shakespeare AS-2 automatic coaxial relay operates as follows:

This automatic switch toggles two radios to one antenna. When you key the microphone on one of the radios, it switches the antenna to it...The radio stays locked onto the antenna until the automatic switch detects a transmit from the other radio.

If the switch works as described, then once you were to transmit on your communication radio, the AIS transponder would no long be connected to the antenna. The AIS transponder would then stop receiving and signals because it was no longer connected to the antenna. Once the AIS transponder transmitted, which will do periodically, it would be reconnected to the antenna. On this basis, your AIS reception would have a period of black out for perhaps as long as three to six minutes following any transmission from your communication radio.

Further, the AIS system requires that all transmissions be self-organized by sharing transmit times. Since a transponder without an antenna connected could not hear any AIS transmissions, it would not know when it was appropriate to transmit. It could transmit randomly and interfere with other vessels's properly timed transmissions.

A better solution for use with an AIS transponder is to have a dedicated antenna for it. The transmit frequency for AIS is far removed from the normal VHF radio transmit frequency, and usually the AIS antenna is retuned for the AIS frequencies to improve performance for the AIS transmitter.

[smac999]

Those switches are crap. Get one that allows both at once. Made for ais

But better for transponder to have own.

[sailjumanji]

I don't think even the Vesper splitter "allows both at once." I think when it senses the VHF is transmitting, then VHF takes priority over the AIS. And the Vesper splitter actually has a signal gain.

I'd recommend buying the Vesper splitter - or at least that is what I did. I didn't want my anything to compromise my Vesper AIS. And I wanted to use the VHF antenna for both, as it is 50+ feet above the water. Have not had any problems with this installation.

[Jim Cate]

Originally Posted by sailjumanji

I don't think even the Vesper splitter "allows both at once." I think when it senses the VHF is transmitting, then VHF takes priority over the AIS. And the Vesper splitter actually has a signal gain.

I'd recommend buying the Vesper splitter - or at least that is what I did. I didn't want my anything to compromise my Vesper AIS. And I wanted to use the VHF antenna for both, as it is 50+ feet above the water. Have not had any problems with this installation.

Agreed! We too use our standard VHF antenna at t he masthead and the Vesper splitter. We routinely receive ships AIS signals at 30-40 miles and other class B signals at 8-12. Our signal is received at similar distances by other yachts. The slight mistuning of the standard antenna is not an issue (after all, AIS signals are sent on frequencies within the normal marine VHF band).

The Vesper splitter has both AIS and VHF rx running continuously. Rx is interrupted when the AIS transmits it's millisecond data burst, and any time the VHF is keyed. This does not have any significant effect upon either service.

A good bit of kit, like most of the Vesper line!

Jim

[chuckr]

We think each antenna has it's own function thus we do not believe in splitters - but a lot of folks do -

[boatbod]

There are a bunch of dedicated AIS antenna suppliers out there. (Raymarine, Simrad, Vesper, ...) Any of them will do a fine job. This device you propose is not intended for AIS and will not work for the reasons already given.

[malbert73]

Thanks everyone.
I figured it wouldn't work and now I know why. Would have been nice to save a couple hundred dollars but not at expense of safety.


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