WLLH Lawrence is back!

chris2526 chris2526@comcast.net
Mon Apr 7 01:29:02 EDT 2008

WLLH Lawrence returned to the air at full power late this afternoon.  As it
turns out there is absolutely no sign of interaction between the two signals 
any more and believe me I drove around back and forth through the spots that 
you could hear a minor blip after the carriers were locked by GPS over 10 
years ago.
The Lowell transmitter was a Harris SX-1 installed in 1985,  I replaced the 
Lawrence RCA BTA-1-R in 1995. Harris was well into the Gates ONE  by that 
time, due to the syncronous nature of the station I prevailed upon Harris to 
build me another SX-1.  The best they could do was come up with enough parts 
to give me an SX-1A and that was the best they could do..

I thought the 99% elimination of the two carrier interactions was as good as 
it could ever get but it appears that using two identical Harris DAX-1's 
pretty much eliminated the last 1%.

Synchronous AM it seems is pretty much perfected but very careful attention
must be paid to the audio, that is why it runs up a T-1 from Boston to Wood 
Hill in Andover where the Optimod 9200 feeds a composite STL feeding one 
dish that points to Lowell which is the tougher path. Lawrence which is line 
of sight
get plenty of signal off the back of the Scala Paraflector.
The original scheme used a splitter into 2 Scalas but by accident having
to use a single dish due to ice damage 10 years ago I was delighted to hear
further reduction of the interaction. When I took over during the Big band 
days on Church St. the station was running a one hope mono RF STL to Lowell
with one Optimod 9000 at the transmitter and a two hop RF STL with a second 
Optimod 9000 at the Lawrence transmitter and things sounded just as bad as 
you would expect using a setup like this.

I grew up in Salem, Ma in the 50's and loved WLLH but had to listen to 
WLLH-FM as I'm sure many of you remember the horrific ( I call it rolling 
phasing )
that plagued WLLH everywhere but in center Lowell and center Lawrence.
In those day they used a creation made by Western Electric that physically
adjusted the frequencies to keep them locked together by motor drives 
similar to the FM frequency control on the very early RCA FM exciters with 
the small scope built in

Later the two RCA's used  an expensive Irridium standard oscillator on each 
transmitter that was marginally better.

Still a few loose ends to tie up but IT"s BAAAACK!

Chris Hall 

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