December 2013 Issue
Table of Contents
Chandlery- December 2013
Vesper AIS-VHF-AM/FM Splitter
The benefits of having Automatic Identification System (AIS) devices on board are obvious (PS, August 2010), but finding a good place for another antenna can be a challenge. Masthead space is often limited and mounting an AIS antenna on the stern rail limits range. Enter Vesper Marine’s VHF/AIS/FM SP160 antenna splitter, a product from the New Zealand-based company that lets your VHF, AIS device, and FM radio share the same antenna.
The submersible SP160 is a well-made, blackbox-type unit that can be used with AIS receivers and transponders, and with 12- or 24-volt DC systems. The splitter features four connectors (VHF, AIS, antenna, and AM/FM radio) and four status-indicating LEDs that show power, VHF transmit, AIS transmit, and antenna quality.
Insertion loss—the loss of signal power resulting from the insertion of a device in a transmission line—is always a concern when installing a splitter. However, the SP160 has a built-in, low-noise amplifier that provides signal gain, improving AIS reception and range, according to the maker.
With the SP160, the VHF radio always has priority and can always transmit, even if power to the unit fails, a feature our testers liked. We also liked the VHF-in-use indicator, which shows when AIS traffic is delayed because the VHF is using the antenna.
Testers installed the SP160 on a Union 36 and found installation to be straightforward. Two 50-ohm patch cables with standard PL-259 plugs are needed, but no special adapters are required for the AIS or VHF connections; the AM/FM connection requires an optional cable.
During initial tests, we noted that AIS reception was improved with SP160 turned on: We picked up one AIS target (at 1.5 nautical miles) with the splitter off; moments later and anchored in the same spot, we picked up 10 targets (up to 11 nautical miles away) with the SP160 turned on. We will be testing the splitter further while cruising this winter.
We generally prefer the simplicity and redundancy of having separate antennas for AIS and VHF. There are always trade-offs when combining the needs of two systems into a single “box,” and splitters are no exception. Using a masthead antenna will provide better AIS reception, but be aware that even modest insertion loss can significantly reduce transmit power output, particularly for longer cable runs with RG-58 coax cable. However, the SP160’s amplifier is designed to compensate for this.
Bottom line: At $249, the SP160 is four times the price of the best VHF antenna in our most recent test (PS, February 2007). But if the thought of running another wire to another antenna gives you a splitting a headache, the SP160 is a viable option.