WLLH-AM Lawrence Facility To Remain Silent For A While
Sun May 6 00:56:24 EDT 2007
Dan Strassberg wrote:
> Because of the great improvements over the last 75 or more years in the
> frequency accuracy and stability of crystal oscillators, most synchronous AM
> operations (and there are probably several dozen in the US in addition to
> WLLH) no longer use special equipment to lock the transmitter frequencies
> together. Instead, the only thing special in most cases is the selection of
> crystal pairs that are well matched in frequency and whose frequencies have
> been shown to behave similarly versus temperature, power-supply voltage, and
> time. So, to a first order, nothing very special would be required to
> synchronize the Waterville and Portland stations other than to make them a
> simulcast and to use a land-line and not a satellite link to supply the
> programming to the station (presumably Waterville) that would not originate
> the programming. The reaon for the use of the land line is the approciable
> time delay to get the signal up to a satellite in synchronous orbit and
> back, but even that could be corrected for by adding a digital time delay
> in the audio feed from the studio to the originating station's transmitter.
As a side note, from time to time in my work I have to deal with low
power AM transmitters for drive-in use. I had an occasion to BS with
one of the factory engineers and somehow the subject of AM
rebroadcasting in tunnels came up. He pointed out that in Boston the
system used one of the local AM stations (I think WRKO) as the system
"clock" for synchronization. The newer systems use the GPS system as
the time base.
Just a side note.
Cinema Service & Supply, Inc.
More information about the Boston-Radio-Interest