Channel Ribs
Well-Known Member
Is it true that duplex fequencies like Ch 80 are not a direct transmission from radio to radio, but are all via a relay station?
Duplex radio frequencies are not direct?
- Thread starter Channel Ribs
- Start date
Birdseye
Well-Known Member
No it isnt. What duplex means is that you transmit on a different frequency to the opne you receive on - so the station talking to you has to be a mirror image. On ch 80 you (the ship station) transmit on 157.025 mc/s and receiuve on 161.625 mc/s. The shore station is vice versa.
If you had the equipment, this would allow you to talk and listen at the same time - assuming you were female and therefore biologically capable of doing so.
/forums/images/graemlins/grin.gif
If you had the equipment, this would allow you to talk and listen at the same time - assuming you were female and therefore biologically capable of doing so.
/forums/images/graemlins/grin.gif
fluffc
Well-Known Member
Amateur Radio Hams use a two-frequency system when bouncing via Repeater Aerials. The Repeater Aerial receives on one frequency and retransmits on another. You need a radio that switches between the two frequencies to use a repeater aerial correctly.
VHF marine systems do not rely on repeater aerials at all.
This is except the Coastguard who have several remote aerials feeding into each shore station.
(In fact any Coastguard station can, technically, listen to ANY coastguard aerial anywhere in the country)
VHF marine systems do not rely on repeater aerials at all.
This is except the Coastguard who have several remote aerials feeding into each shore station.
(In fact any Coastguard station can, technically, listen to ANY coastguard aerial anywhere in the country)
Channel Ribs
Well-Known Member
[ QUOTE ]
(In fact any Coastguard station can, technically, listen to ANY coastguard aerial anywhere in the country)
[/ QUOTE ]
I was entertained to hear Solent CG getting a radio check from Dover CG the other day, Dover reported a good signal from their Newhaven aerial - which is of course inside Solent's area of opperation.
My record is recieving Swansea CG at my workshop in Kent, high pressure or bouncy ionosphere?
(In fact any Coastguard station can, technically, listen to ANY coastguard aerial anywhere in the country)
[/ QUOTE ]
I was entertained to hear Solent CG getting a radio check from Dover CG the other day, Dover reported a good signal from their Newhaven aerial - which is of course inside Solent's area of opperation.
My record is recieving Swansea CG at my workshop in Kent, high pressure or bouncy ionosphere?
Bilgediver
Well-Known Member
The difference between duplex and simplex is that in simplex both stations transmit on the same frequency so can only speak one at a time and no good for fax etc.
Duplex as channel 20 to 28 etc has two frequencies for each channel with the ship transmitting on one frequency and the coast staion on a different one. and on full duplex both stations can talk at the same time and send faxes.
Must ships actually work semi duplex as their equipment can not transmit and receive at the same time so you have to press the tit to send and release to receive just like simplex. However any ship eavesdropping will only hear the coaststation and not the other ship.
The only relay may be a function of landline relay from the coast station to the transmitter .
John
Duplex as channel 20 to 28 etc has two frequencies for each channel with the ship transmitting on one frequency and the coast staion on a different one. and on full duplex both stations can talk at the same time and send faxes.
Must ships actually work semi duplex as their equipment can not transmit and receive at the same time so you have to press the tit to send and release to receive just like simplex. However any ship eavesdropping will only hear the coaststation and not the other ship.
The only relay may be a function of landline relay from the coast station to the transmitter .
John
Channel Ribs
Well-Known Member
But, how does that fit in with Ch 80? Where marina staff can talk and hear but we can only hear them, not other sailors?
john_morris_uk
Well-Known Member
[ QUOTE ]
My record is recieving Swansea CG at my workshop in Kent, high pressure or bouncy ionosphere?
[/ QUOTE ] Almost certainly NOT the ionosphere. The phenomona is known as 'ducting' and is usually associated with high pressure.
My record is recieving Swansea CG at my workshop in Kent, high pressure or bouncy ionosphere?
[/ QUOTE ] Almost certainly NOT the ionosphere. The phenomona is known as 'ducting' and is usually associated with high pressure.
shmoo
Well-Known Member
Boats listen on the freq marinas transmit on. Marinas listen on the freq boats transmit on. These two freqs are different (duplex). It follows boats don't listen on freq other boats transmit on, and so can't hear them.
fireball
Well-Known Member
http://www.merseyshipping.co.uk/minfo/marineradio/MarineFreq1.htm
Chl 80
A Ship VHF set will transmit on 157.025 and receive on 161.625Mhz
A Coastal Station (ie marina) is the other way round - transmit on 161.625 and receive on 157.025Mhz
80 157.025 161.625
Chl 80
A Ship VHF set will transmit on 157.025 and receive on 161.625Mhz
A Coastal Station (ie marina) is the other way round - transmit on 161.625 and receive on 157.025Mhz
80 157.025 161.625
Channel Ribs
Well-Known Member
So marina staff can't talk to each other on Ch80?
fireball
Well-Known Member
In short - no
on a duplex channel you can only talk to someone with the opposite setup - so mobile staff could have normal handhelds and talk with the base station, but they could not converse between themselves.
I quite often think it is daft to have the marinas on CH80 - as you cannot tell when the frequency is clear to call - how often do two vessels call up at the same time (probably not as many as the number calling marinas on Ch16 ... as heard yet again on Sunday!! Shepards Wharf do NOT monitor CH16!!).
on a duplex channel you can only talk to someone with the opposite setup - so mobile staff could have normal handhelds and talk with the base station, but they could not converse between themselves.
I quite often think it is daft to have the marinas on CH80 - as you cannot tell when the frequency is clear to call - how often do two vessels call up at the same time (probably not as many as the number calling marinas on Ch16 ... as heard yet again on Sunday!! Shepards Wharf do NOT monitor CH16!!).
pelicanpete
Well-Known Member
If you used two sets; one switched to Int on CH80 and the other (say a handheld, as in my case) switched to US on CH80A, you can hear both sides of the conversation...
Kawasaki
Well-Known Member
I find all this very interesting Malt
Good questions and answers on ere.
I also have wondered why sometimes we can hear the Coastgaurd/ Marina and not the Call station.
I lament the demise of Coast Radio Stations too.
I thought it was great when I could call SWMBO from My little ship, to the Land Line.
Plus one could "listen in " To others!
My "fixed radio" is on the Blink
Must find a proper firm that can supply a "Back Up"
Any ideas? /forums/images/graemlins/tongue.gif
Good questions and answers on ere.
I also have wondered why sometimes we can hear the Coastgaurd/ Marina and not the Call station.
I lament the demise of Coast Radio Stations too.
I thought it was great when I could call SWMBO from My little ship, to the Land Line.
Plus one could "listen in " To others!
My "fixed radio" is on the Blink
Must find a proper firm that can supply a "Back Up"
Any ideas? /forums/images/graemlins/tongue.gif
Bilgediver
Well-Known Member
It does......Channel 80 is Duplex and as you have said you can work the marina staff and you can hear them and they can hear you and you cannot hear other ships as it is duplex....if the marina is fitted with talk through facilities....like the police.....then the marina staff can talk to each other. Mind you the marina staff could also possibly have radios with channel 80 and channel 80 reversed in which they could talk to each other on channel 80 reversed and to the office on channel 80.
The duplex channels are reversed in shore stations.
The duplex channels are reversed in shore stations.
Channel Ribs
Well-Known Member
[ QUOTE ]
Any ideas? /forums/images/graemlins/tongue.gif
[/ QUOTE ]
Ah, what you need is the new Phllips miniShuttle Satcom set up... In the event that it can't get a ground or satelite signal it launches one of it's own. /forums/images/graemlins/wink.gif
I can send you a demo tape if you like? /forums/images/graemlins/tongue.gif
Any ideas? /forums/images/graemlins/tongue.gif
[/ QUOTE ]
Ah, what you need is the new Phllips miniShuttle Satcom set up... In the event that it can't get a ground or satelite signal it launches one of it's own. /forums/images/graemlins/wink.gif
I can send you a demo tape if you like? /forums/images/graemlins/tongue.gif
whipper_snapper
Well-Known Member
[ QUOTE ]
I also have wondered why sometimes we can hear the Coastgaurd/ Marina and not the Call station.
[/ QUOTE ]
That is sometimes because it is a duplex frequency.
More often (and always on simplex channels such as ch16) it is simply because the CG has a bloody great aerial on top of a mountain and killowatts of power while the caller is a small boat with an aerial a few feet up and 25W of power.
I also have wondered why sometimes we can hear the Coastgaurd/ Marina and not the Call station.
[/ QUOTE ]
That is sometimes because it is a duplex frequency.
More often (and always on simplex channels such as ch16) it is simply because the CG has a bloody great aerial on top of a mountain and killowatts of power while the caller is a small boat with an aerial a few feet up and 25W of power.
