Re: WBZ--WBZA

[Dan Strassberg <dan.strassberg@worldnet.att.net>]

At 10:51 PM 7/13/97 +0000, you wrote:

>Beyond their plant, there is an abandoned brick
>building located on top of a small hill. This building housed the original
>transmitting equipment of Radio Station WBZ in the 1930s.  Two 150-foot
>towers held the station's antennas.  After WBZ moved to its present
>Brighton location, this facility was used by the Federal Communications
>Commission as a radio monitoring station.  It was abandoned about 1950."
>
Despite the two towers, I don't think the station was directional. For one
thing, the first reported use of a DA in the US was in 1931 at WSUN, St
Petersburg FL. I think it was customary, in those days, to use short,
self-supporting towers to support AM TX antennas. Unlike modern AM antenna
towers, the towers did not themselves radiate--at least not intentionally.
Rather, a wire (or several parallel wires--I've heard them referred to as a
"bedspring") were run between the self-supporting towers. The actual antenna
was suspended from this wire or wires. The TX building was usually right at
the base of the antenna. Besides holding up the top of the antenna, the
bedspring (or single horizontal wire) served as a top-load. If WBZ was on
990 and the towers were 150' high, the vertical portion of the antenna was
54.4 degrees. With a decent ground system, that's just high enough for an
effective field of 175 mV/m/kW unattenuated at 1 mile. I suspect that that
efficiency, which is now the minimum for Class B stations, was quite
respectable in its day. But the top load must have made the efficiency
higher--perhaps as high as the currently required value for Class A AMs--225
mV/m/kW unattenuated at 1 mile.

When I was at RPI, from 1952 to 1956, WHAZ, which was then owned by the
Institute, transmitted from such an antenna. The two towers were atop the
Russell Sage Laboratory, the EE building on the RPI campus. The ground
system was the building's copper roof. The towers were much shorter than
150' and I'm sure that the antenna efficiency was less than the normal
minimum but was grandfathered. WHAZ was a very old station even then; it
went on the air in 1922.

For many years, WOR had one of the more interesting AM TX antennas. It was
sort of a hybrid between this old style and current technology, and was
located in Carteret NJ, near Staten Island. The antenna looked like a tall
version of what I described. In this case, though, it WAS a directional and
the two self-supporting towers WERE part of the array.

The pattern was a figure 8 with one lobe to the northeast over New York City
and toward Hartford. The southwest lobe was directed toward Philadelphia.
WOR, which was licensed to Newark when the array was built, must have used
the array from the late 1920s until the early 1960s, when the station moved
its TX to it present location in Lyndhurst NJ, west of midtown Manhattan.

I've only seen a picture of WOR's Carteret setup and a map of the old 0.5
mV/m contour. I have no info on the tower dimensions, spacing, or
orientation or the antenna efficiency. I also don't know whether the old
array was "end-fire" or "broadside." That is, I don't know whether the
towers were on a northwest to southeast line (broadside) or a southwest to
northeast line (end-fire). Both arrangements are possible, although I think
the broadside arrangement is more likely. It would have taken advantage of
the normal shielding effect of the self-supporting towers, which tended to
create weak nulls in what were supposed to be omnidirectional patterns.

It would be interesting to see a map that shows the location of the towers
at the WBZ Millis site. One might think that the towers might have been on a
west-northwest to east-southeast line. That would have directed one of the
unintentional (but still unavoidable) nulls toward Springfield to minimize
interference to WBZA and the other to the south of Boston.

- -------------------------------
Dan Strassberg (Note: Address is CASE SENSITIVE!)
ALL _LOWER_ CASE!!!--> dan.strassberg@worldnet.att.net
(617) 558-4205; Fax (617) 928-4205

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