VHF channels for marine operator? 24 - 28 and 84 - 87
 

"Scott Downey" wrote in message
...
Ok that makes sense that other boaters would only hear the coast guard
shore
station, BUT what about the guy on the boat the CG shore station is
talking
to?

It is common for the shore station to rebroadcast the ships signal so that
all can hear it. This technique is often referred to as a "repeater".

I don't know about any other country, but here is a link to the US Coast
Guard's web page that provides information regarding what channels are used
for what:

http://www.navcen.uscg.gov/marcomms/vhf.htm


There are 51 channels in this list. One of these is a "receive only" (with
respect to the boat) channel. Ten of these are "duplex" channels, where the
transmit and receive frequencies are different. Of these 10, 8 are
designated as "Public Correspondence (Marine Operator)". One is designated
"Automatic Identification System duplex repeater". Only one, channel 20, is
used for official use: "Port Operations (duplex)"

I haven't listened in on the port operations much, but I suspect that they
would operate in the "repeater" mode. On this channel, the ship transmits on
a frequency of 157.000 MHz. The port office has a radio that is listening
on 157.000 MHz, and transmits on 161.600 MHz. The port office can transmit
directly, or it can take the signal it received and transmit it again on
161.600. If it is in repeat mode, all the ships within range can hear the
entire conversation. This would be very helpful in coordinating traffic
between ships that might be out of range with each other but within range of
the port (which would have the benefit of a much taller antenna and possibly
a better receiver and more powerful transmitter).

It has been a number of years since I have heard any Marine Operator traffic
on VHF. Before cell phones, marine operator traffic was fairly common. If
a ship wanted to place a call, they would contact the marine operator on
channel 16. The operator would instruct them to go to a specific duplex
channel where the call would be made. Let's say that the operator directed
you to channel 28. The boat would transmit on frequency 157.400 and receive
on 162.000. The marine operator would do the opposite. Since the person at
the other end of the phone line can't "push to talk" the marine operators
transmitter is going all the time, transmitting whatever it gets from the
phone line.

When the call was connected, the very nature of the telephone line "repeats"
the boats signal. Just like you hear your own voice in the earpiece when
you talk on the phone, the marine operators transmitter will hear the
skipper's voice after it has looped through the telephone central office. A
third party eavesdropping on the channel will be able to hear the entire
conversation.

Rod McInnis

VHF channels for marine operator? 24 - 28 and 84 - 87
 

"Scott Downey" wrote in message ...
sure, the duplex channels are separated so each person transmitting does not
step on the other persons transmission, therefore both could talk and be
heard if you had 2 radios or a special radio where you could hear and talk
at the same time.

But if you have 2 boaters both on the same duplex channel talking to one
shore station on its own complemntary channel, each boater should be part of
the same conversation. There would be no difference between them as they
would both be using the same duplex channel. So therefore another boater
ought to be able to listen in if tuned to the same duplex channel that the
other boater was using talking to the shore station.

Yeah. You can listen in on the transmissions from the shore station,
not the other boats.

If two boats are talking to a shore station on, say, channel 84. both
of the boats will only hear the shore station, not eachother.

Think off a tin can telephone system. With one string (frequency) you
are simplex. In theory you can't hear the other guy talking when you
are talking because you have the can to your mouth instead of your
ear. Only one person can talk at a time, but only one string is
needed for a two-way comm.

With duplex there are two strings (frequencies). The string from your
transmitter is connected to shore station's receiver. That string
only goes one way. The other string goes from the shore station's
transmitter to your receiver. Again it's only one way on each string.

The other boats' strings are set up the same way. The only way to
hear other boats would be to swap the strings on your radio. You
can't do that.

Does anyone sell a special radio that allows one to hear and talk at the
same time? I dont see that in the catalogs. Using 2 radios is a work around,
I suppose.

The only thing that would allow is for you to transmit and receive
simultaneously (full duplex as opposed to half duplex). It will not
change the frequency set and allow you to talk to other boats on a
duplex channel.

VHF channels for marine operator? 24 - 28 and 84 - 87
 

"Rod McInnis" wrote in message ...
"Scott Downey" wrote in message
...
Ok that makes sense that other boaters would only hear the coast guard
shore
station, BUT what about the guy on the boat the CG shore station is
talking
to?

It is common for the shore station to rebroadcast the ships signal so that
all can hear it. This technique is often referred to as a "repeater".

I don't know about any other country, but here is a link to the US Coast
Guard's web page that provides information regarding what channels are used
for what:

http://www.navcen.uscg.gov/marcomms/vhf.htm


There are 51 channels in this list. One of these is a "receive only" (with
respect to the boat) channel. Ten of these are "duplex" channels, where the
transmit and receive frequencies are different. Of these 10, 8 are
designated as "Public Correspondence (Marine Operator)". One is designated
"Automatic Identification System duplex repeater". Only one, channel 20, is
used for official use: "Port Operations (duplex)"

I haven't listened in on the port operations much, but I suspect that they
would operate in the "repeater" mode. On this channel, the ship transmits on
a frequency of 157.000 MHz. The port office has a radio that is listening
on 157.000 MHz, and transmits on 161.600 MHz. The port office can transmit
directly, or it can take the signal it received and transmit it again on
161.600. If it is in repeat mode, all the ships within range can hear the
entire conversation. This would be very helpful in coordinating traffic
between ships that might be out of range with each other but within range of
the port (which would have the benefit of a much taller antenna and possibly
a better receiver and more powerful transmitter).

It has been a number of years since I have heard any Marine Operator traffic
on VHF. Before cell phones, marine operator traffic was fairly common. If
a ship wanted to place a call, they would contact the marine operator on
channel 16. The operator would instruct them to go to a specific duplex
channel where the call would be made. Let's say that the operator directed
you to channel 28. The boat would transmit on frequency 157.400 and receive
on 162.000. The marine operator would do the opposite. Since the person at
the other end of the phone line can't "push to talk" the marine operators
transmitter is going all the time, transmitting whatever it gets from the
phone line.

When the call was connected, the very nature of the telephone line "repeats"
the boats signal. Just like you hear your own voice in the earpiece when
you talk on the phone, the marine operators transmitter will hear the
skipper's voice after it has looped through the telephone central office. A
third party eavesdropping on the channel will be able to hear the entire
conversation.

Hearing youself on the telephone receiver is called sidetone. Phone
connection made through trunks don't necessarily have sidetone.
However you are correct that you could often hear the ship side of the
call on the receive side of the channel.

Rod McInnis

VHF channels for marine operator? 24 - 28 and 84 - 87
 

Thanks for all the good help.

I believe, now I understand .


"Curtis CCR" wrote in message
om...
"Scott Downey" wrote in message
...
sure, the duplex channels are separated so each person transmitting does
not
step on the other persons transmission, therefore both could talk and be
heard if you had 2 radios or a special radio where you could hear and
talk
at the same time.

But if you have 2 boaters both on the same duplex channel talking to one
shore station on its own complemntary channel, each boater should be
part of
the same conversation. There would be no difference between them as they
would both be using the same duplex channel. So therefore another boater
ought to be able to listen in if tuned to the same duplex channel that
the
other boater was using talking to the shore station.

Yeah. You can listen in on the transmissions from the shore station,
not the other boats.

If two boats are talking to a shore station on, say, channel 84. both
of the boats will only hear the shore station, not eachother.

Think off a tin can telephone system. With one string (frequency) you
are simplex. In theory you can't hear the other guy talking when you
are talking because you have the can to your mouth instead of your
ear. Only one person can talk at a time, but only one string is
needed for a two-way comm.

With duplex there are two strings (frequencies). The string from your
transmitter is connected to shore station's receiver. That string
only goes one way. The other string goes from the shore station's
transmitter to your receiver. Again it's only one way on each string.

The other boats' strings are set up the same way. The only way to
hear other boats would be to swap the strings on your radio. You
can't do that.

Does anyone sell a special radio that allows one to hear and talk at the
same time? I dont see that in the catalogs. Using 2 radios is a work
around,
I suppose.

The only thing that would allow is for you to transmit and receive
simultaneously (full duplex as opposed to half duplex). It will not
change the frequency set and allow you to talk to other boats on a
duplex channel.