"David Eduardo" wrote in message
...

"Dan Robbins" wrote in message
...

There's a Franklin at N 41.6 and w 93.3:


http://www.desmoinesbroadcasting.com...use _9867.jpg


I don't know if it still exists, but KELO 1320 used to even advertise it had
a Franklin.

In deference to Steve who says the previous thread is dead, let me answer David's
question about KDKA's "Franklin"....but only to say that KDKA's Franklin wasn't truly
that. A Franklin radiator looks like two self-supporting towers, one inverted on top
the other, fat ends touching. The one such that I remember (and I'd have to think
that most of us have seen the picture) is WLW's tower that participated in the
superpower experiments in the 30s. KDKA's radiator was simply described in the
license as a center-fed vertical radiator, where the base impedance and input power
was determined through quasi-indirect means at the input to the balun necessary to
match the balanced feed point with the unbalanced transmission line (in years past,
this stick was fed with balanced feed line, not unlike VHF twin lead on acid...hams
know this feed line as "ladder" feedline, because of the characteristic cylindrical
insulators placed at regular lengths along the conductors to maintain the correct
separation between those conductors).

KDKA's antenna was fairly broadbanded, which if I remember correctly is a feature of
center-fed radiators. But WLW's Franklin, because of the larger cross-section where
current was higher, had a very nice, minimally-sloped reactance curve, and thus a
very consistent, symmetrical impedance...if you ever heard WLW when they played music
in the 70s, it really sounded great. KDKA's system had, of course, a ground system,
to help pull down the skywave, but due to the fact that my manager (who shall go
nameless to protect the embarassed) let the neighborhood kids ride their BMX
motorcycles on the property (she thought that the presence of life on the transmitter
grounds would deter vandalism), breaking a significant number of radials that were
exposed by rutting after heavy rains dredged out the BMX paths, it didn't work all
that well...on solar max periods, we'd often get fading well within our local metro
coverage area because so much power went skyward and came back down, just slightly
out-of-phase with the ground wave.

The antenna I had direct experience with was replaced in the mid 90s, but from what
I've heard the only thing that was changed was the steel....the basic design was
retained, and the counterpoise was repaired.
--
-----------------------------------------------------------------------------
If there's nothing that offends you in your community, then you know you're not
living in a free society.
Kim Campbell - ex-Prime Minister of Canada - 2004
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For direct replies, take out the contents between the hyphens. -Really!-

A Franklin radiator looks like two self-supporting towers, one inverted on top
the other, fat ends touching.


Nope.

A Franklin is defined as a center-fed sectional, which is 180 degrees over 180
degrees. The base of the bottom section is connected to the ground system by an
impedance, usually a capacitor.

KSTP's Franklin is not a Frankin on account it is 179 degrees over 179 degrees.

A true Franklin has an efficiency of 510 mV/m/kW at 1 km.

KSTP's certainly equals that, although it is classified by the FCC as a
conventional sectional.

KDKA's sectional is just that.

As was WOAI's. 120 degrees over 120 degrees.

WHO's radiator isn't a Franklin, either, it is a "WHO Type", and is so
classified by the FCC. It is 300 degrees tall.

A true Franklin has the best horizontal field of any radiator.

A WHO-type radiator probably has the best anti-fading performance of any
radiator.

A Franklin radiator looks like two self-supporting towers, one inverted on top
the other, fat ends touching.


Naw ... that's a Blaw-Knox, named for the company which manufactured them.

Not many still standing today.

"Peter H." wrote in message
...


A Franklin radiator looks like two self-supporting towers, one inverted on
top
the other, fat ends touching.


Naw ... that's a Blaw-Knox, named for the company which manufactured them.

Not many still standing today.

I think there are a couple. New Hampshire (WFEA?), WSM, WLW, and the WBT
installation. WADO took theirs down when the new 50 kw DA was built 3-4
years ago.

Peter H. wrote:


A Franklin radiator looks like two self-supporting towers, one inverted on top
the other, fat ends touching.


Nope.

A Franklin is defined as a center-fed sectional, which is 180 degrees over 180
degrees. The base of the bottom section is connected to the ground system by an
impedance, usually a capacitor.

So it is asymmetric, with the two sections slightly different lengths, or the
base capacitor is used to compensate for that?

If it were in free air, it would simply be a vertical dipole, but since the
ground is below it, the electrical lengths of the bottom leg is changed,
right?

KSTP's Franklin is not a Frankin on account it is 179 degrees over 179 degrees.

What does this do to the pattern in real terms?
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

If it were in free air, it would simply be a vertical dipole, but since the
ground is below it, the electrical lengths of the bottom leg is changed, right?


It's not a dipole over a perfectly reflecting earth because: 1) the top section
is series excited from the center of the coax feed line through a network, 2)
the outer cover of the coax feed line is directly connected to the top of the
bottom section, and 3) the bottom of the bottom section is connected to the
ground system through another network, usually just a capacitor.

This results in the current distribution being changed such that: 1) the
horizontal field is greatly increased over that of a 180 degree radiator, and
2) the vertical field is greatly reduced over that of a radiator which is
taller than 180 degrees.

Ordinarily, a 225 degree radiator has the maximum horizontal field, but such a
radiator also has a very significant vertical field ... significant enough to
cause loss of primary service area due to the reflected vertical field being
approximately equal to, but of opposite polarity to the horzontal field at its
extremes.

Hence, 200 degrees is normally the tallest conventional vertical radiator used
for Class A stations.

And, Class A stations which use an unsectionalized radiator taller than 200
degrees do so at their peril.

(There are only two such cases within the U.S., and I don't know of any outside
of the U.S.).



KSTP's Franklin is not a Frankin on account it is 179
degrees over 179 degrees.

What does this do to the pattern in real terms?


Nothing, which is why I also stated that a true Franklin and a Franklin-type
sectional which is just a tad shorter than a true Franklin (the KSTP day
radiator case) BOTH have an efficiency of 510 mV/m/kW at 1 km.