BoatBanter.com - View Single Post - VHF

wrote:
Guys,

does anybody know what difference it makes if a channel is simplex or
duplex? Seems to be that either way the result is the same?

Matt

As mentioned in other posts, duplex refers to using different
frequencies for transmit and receive.

Your cellphone is handy example of a "full duplex" transceiver. In the
800MHz cell band your phone transmits and receives simultaneously on
frequencies that are 45MHz apart. This is how it allows you to talk
and listen at the same time.

The duplex channels on your VHF are generally used for marine operator
or other public coast stations handling message traffic for boats and
ships.

The marine operators' stations operate in full duplex on these
channels. Ship stations with the appropriate equipment can also run
full duplex, but I understand that it is less common now as "telephone"
traffic for most is now going by satellite.

Most of use with standard VHF radio run "half duplex" on our end. We
are still using different frequencies for transmit and receive, but we
cannot transmit and receive simultaneously. Though you can get the
"full duplex" effect with two VHF radios if you set the antennas up
correctly.

If you attempt to communicate ship to ship on a duplex channel, it
won't work. Ships use the same transmit freq for transmit and same
freq for recieve. The coast stations are set up opposite. You
transmit on the the coast station's receive freq - they hear you. They
transmit on your receive freq - you hear them.