Re: WLLH-AM Lawrence transmitter off-air

["Dan Strassberg" <Dan.Strassberg@worldnet.att.net>]

Bingo! Absolutely correct. Engineers have been fiddling with synchronization
schemes for AM TXs since the 20s, when oscillator frequency stability was
dreadful by the standards of even 20 years ago. What a thread could get
started on this one--if anyone had enough details; unfortunately, even I am
not old enough to remember any of the sync deals first-hand. Back when the
whole sync idea started, there was apparently no appreciation of phase noise
in frequency multipliers. The scheme that was apparently most often used was
to divide the "master" station's carrier down to audio, send the audio over
ordinary phone lines, and multiply the frequency back up to the original at
the "slave" station. Unless the divider and multiplier have zero phase
noise, the nulls between the two signals walk around within the hash zones,
giving the listener the same effect as a beat note between carriers at
slightly different frequencies. It's best if the hash zones can be confined
to areas where hardly anyone lives. In such cases, the frequency stability
of today's crystal oscillators is quite good enough. Best example is KIPA in
Hilo HI on 620. KIPA runs 5 kW-U ND and has two "synchronous" TXs, one with
5 kW-U ND and the other with 10 kW-U ND (and a Paran antenna--but that's yet
another thread). They are all on the same island--at different points along
the coast, but it's a large, triangular-shaped island and is very sparsely
populated between the major communities on the coast and pretty much
everywhere inland. The hash zones mostly exist in the areas of low
population density.

--

Dan Strassberg, dan.strassberg@worldnet.att.net
Phone: 1-617-558-4205, eFax: 1-707-215-6367

-----Original Message-----
From: SteveOrdinetz <steveord@wavewizard.com>
To: dan.strassberg@att.net <dan.strassberg@att.net>
Cc: BostonRadio <boston-radio-interest@bostonradio.org>
Date: Monday, January 10, 2000 11:32 PM
Subject: Re: WLLH-AM Lawrence transmitter off-air


>Does there need to be phase synchronization as well as frequency sync for
>this to work?  It would seem to me that if the signals were in phase with
>each other the hash zone would be smaller.
>