WLLH-AM Lawrence Facility To Remain Silent For A While

[Dan Strassberg]

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.

If the stations do not significantly interefere with each other in
"non-synchronous" mode, little would be gained in coverage by synchronizing
them. If they do significantly interfere, the area of audible interference
would be replaced by what used to be known as a "hash zone" but now would
more properly be descibed as an area of standing-wave interference, in which
the signal strength would slowly vary in a periodic manner. The receiver's
AGC substantially mitigates this slow variation. Since 1490 is a "graveyard"
frequency, with very high background QRM at night from dozens of co-channel
stations, there would be no area of audible nighttime interference between
the Portland and Waterville signals. The minimal benefit of synchronization
would thus exist only during daylight hours.

--
Dan Strassberg, dan.strassberg@att.net
eFax 707-215-6367

----- Original Message -----
From: "Dan Billings" <billings@suscom-maine.net>
To: "Laurence Glavin" <lglavin@mail.com>;
<boston-radio-interest@rolinin.bostonradio.org>
Sent: Saturday, May 05, 2007 9:55 PM
Subject: Re: WLLH-AM Lawrence Facility To Remain Silent For A While


> The WLLH operation brings a question to mind:
>
> If the 1490 in Waterville, Maine and the 1490 in Portland, Maine were to
> simulcast, would it improve the coverage area of the two signals?
>