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I am sure you know:

http://www.navcen.uscg.gov/?pageName=mtvhf



2013/8/29, Lu Abel :
> I live in the San Francisco Bay area and there's this little thing going
> on called the America's Cup.
>
> It's being broadcast on TV (at least here in the USA), usually after a
> two hour delay (ie, after the actual races have concluded so as to not
> draw people away from watching in person shoreside).
>
> The audio from the broadcast, which included real-time reporting and
> commentary by sailing luminaries such as Gary Jobson, is broadcast live
> on Marine VHF frequency 20, so you can actually hear the commentary as
> you watch the races from your boat (as I did a couple of weekends ago).
>
> Here in the US about a third of the VHF radio channels we use are
> different from what the rest of the world uses.   Generally they are
> simplex channels whereas their international brothers are duplex. These
> US-unique channels are often designated with an "A" after the channel
> number (for example, to talk to the US Coast Guard, one uses Ch 22A)
>
> Because of this difference, most VHF marine radios come with a switch
> labeled "USA" and "International" that switches between the two sets of
> frequencies.
>
> I got into a confusing argument with several very knowledgeable
> colleagues about the America's Cup broadcasts because they were
> broadcast on Channel 20, not 20A.   "That requires switching your radio
> to 'International' to listen, doesn't it?"   "No, it's just on my
> radio"  I finally discovered that both Channel 20 (duplex) and 20A
> (simplex) are authorized for use in the USA.
>
> I've got a fixed mount radio on my boat and two hand-held VHFs, all of
> which are 10 or more years old.   They give me just one choice of VHF
> Channel 20 (which I'm guessing is 20A).    (I also just bought a new DSC
> VHF radio, but haven't had a chance to install it and see a 2013 view of
> channels)
>
> Adopting both 20 and 20A for use in the USA seems to be recent. But I
> can find no information about when this change took place.
>
> Does anyone on this list know (or, even better, point to some history on
> the adoption)?
>
> Thanks
>
> Lu
>
> : http://fer3.com/arc/m2.aspx?i=125004
>
>
>

   

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