Originally Posted by malbert73
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.