Not quite right. Half duplex channels are split frequencies (2
frequencies) like the marine operator channels. The base stations are
full duplex (can transmit and receive at the same time) but the ship
station is usually "half duplex", meaning it is operating on a duplex
channel but still requires push to talk. This mode allows the ship
station to interrupt the shore station at any time.

A half duplex channel is the same as a full duplex channel (pair).
They are really two frequencies capable of full duplex but may be used
only half duplex. Depending on the radio used. Each radio receives on
the oposite frequency it transmits on.

Being "half duplex" means that half of the circuit is duplex (base
station) and the other half (ship) is not duplex. The ship station
could operate a full duplex radio and then the circuit would be full
duplex. There are some full duplex ship station radios.

A "Simplex" channel means that only one frequency is involved. Both
stations transmit and receive on the same frequency. One must listen
while the other transmits. Like channel 16.

There are some full duplex headsets available. Meaning no vox
involved. You both can talk back and forth just like you are on the
telephone.
I don't know if there are any that are inexpensive though.

The ones with the vox in them are really "simplex" units. Meaning they
both operate on the same frequency and rather than push to talk, the
vox operates the push to talk for you.

These type of headsets mostly operate in unlicensed frequencies. They
are usually very low power and have short range.

Regards
Gary


On Thu, 3 Jul 2003 16:40:18 -0700, "Chuck Tribolet"
wrote:

The problem is that only a few of the VHF channels are full
duplex. Most are half-duplex (what you call simplex, but that's
not accurate -- simplex is one way only, like AM and FM broadcast
radio).