Re: The Colonial Network

[Dan.Strassberg@att.net]

I've read that WNAC and WAAB diplexed from a tower in Quincy. As a Quincy 
resident, Donna might know where it was. This probably wasn't the very first 
example of an AM diplex, but it certainly must have been an early one.

For the day, the setup must have been quite advanced, because diplexing gets 
trickier the closer the stations are in frequency. The 180-kHz frequency 
difference was only 12.77% of the higher carrier frequency. Decades later--
around 1980--I was told that a good rule of thumb is not to attempt diplexing 
of AM stations whose frequency difference is less than 10% of the higher 
carrier frequency. Indeed, even now, there are only a few examples of AM 
diplexes in which the frequency difference is less than 10% of the higher 
frequency. Certainly the design of passive filter networks was pretty well 
understood in the 30s, but a lot of synthesis techniques that today are 
considered standard did not exist until much later, and, of course, computer 
analysis was nonexistent. 

That WAAB and WNAC shared a single vertical radiator as early as 1936 suggests 
that Shepard had some forward-thinking engineers and was willing to invest in 
his properties' technical facilities. Many stations continued to use 
horizontal "long-wire" antennas well past the mid thirties.

The best known of these was probably that of KPO (now KNBR) San Francisco, a 50-
kW ex-class IB clear-channel station, which, in the 30s, was (I believe) owned 
by NBC. The KPO transmitter was at the Palo Alto site of the current KNBR Tx. I 
believe that the old long wire wasn't replaced with a vertical tower until 
after World War II ended. Most likely, the initial delay was the result of the 
site being in the glide path to San Francisco International Airport. Then World 
War II probably prevented the construction.

NBC was probably not interested in a move to the East Bay, where nearly all of 
the other San Franciosco AMs are located, because the peninsula location with 
the salt marshes of the Bay to the east provides unequaled coverage inland. 
Most of the SF/Oakland AMs are directional to the west to protect inland 
stations and so must be (or should be) located in the East Bay. KNBR, however, 
is 50 kW ND-U. 

--
dan.strassberg@att.net
617-558-4205
eFax 707-215-6367

> Kevin wrote:
> >Any idea on how the signals of WNAC and WAAB compared back then?
> 
> In 1940, before NARBA moved everybody in early 1941, WAAB had a dial 
> position of 1410, with 1000 wonderful watts.  WNAC was still stuck at 1230 
> kHz, with 5000 watts day and 1000 watts night.
> 
>