[BC] Nighttime operation by daytimers

[Dan Strassberg]

Mark Humphrey wrote:
"Those of you with daytimers authorized for "flea power" at night should be
aware that the FCC has (in at least one case) allowed two-site operation
with a short (18 degree) nondirectional antenna at the night site."

Would this be one of Kintronics' very short and heavily top-loaded new
KinStar antennas? I believe that the FCC recently approved the KinStar
design for use at higher powers on (nondirectional) Class B, C, and D AMs
without requiring the applicants to make any special showings of the
vertical radiation characteristics. The widely respected Louis duTreil
published papers showing that the KinStar's vertical radiation
characterisitcs are very similar to those of conventional series-fed
antennas approximately 1/4-wavelength in height.

One of duTreil's/Kintronics' major contributions to the technology of short
AM radiators was the design of matching networks for the very low
driving-point impedance of these (approximately 0.2-wavelength) structures.
The info on the matching networks is also contained in papers by duTreil,
which I believe you can either download directly from Kintronics' Web site
or are linked from the site.

As for Class D AMs using separate day and night sites, I know of two and I'm
pretty sure there are several more. One is the 10-kW directional daytimer on
670 near Chesapeake Bay in Virginia. In addition to a very low-power night
operation from its main site, this station also maintains an "experimental"
nighttime synchronous Tx 30 or more miles to the southeast at the site of a
co-owned station in Portsmouth or Virginia Beach--in the heart of the 670
station's target market. The station that hosts the synchronous site
operates at approximately twice 670 kHz and has a three- or four-tower DA.
The 670 station uses those towers as its own DA to protect WSCR, and runs
several hundred watts from them. The towers are too short to achieve
standard efficiency at 670, but because the FCC considers the synchronous Tx
to be experimental, I guess the low efficiency is OK.

I think, though, that the other two-site daytimer I know of is my favorite:
WRDT 560 Monroe MI. Despite being licensed to a community half-way between
Detroit and Toledo and using a daytime power of only 500W, the station
delivers a decent daytime signal to the Motor City thanks to the low dial
position, good soil conductivity, and a four-tower array that aims a teardop
pattern right at Detroit. But I find the 13W night operation even more
fascinating: At 990', the radiator is, to my knowledge, the tallest in use
on AM in the US! WRDT operates at night from a folded unipole antenna on an
FM-TV-communications tower known as the MoTower in (I believe) Southfield,
more than 40 miles north of WRDT's day site. 13W at 560 into that 200-degree
nondirectional stick probably does a pretty nice job for WRDT.

--
Dan Strassberg, dan.strassberg at att.net