[BC] Conductivity vs Skywave

[PeterH5322@aol.com]

>Plus you must consider we're talking electrical length here. Physical length
>is usually less then electrical due to the area of the tower. An example is
>WEEI in Boston. They use 180 degree towers. Unfortunately, they also have 10
>foot faces. This makes their electrical length more then the physical one.
>It's also why you hear a lot of seclective fading at night on this station
>about 30-50 miles from the transmitter. The towers (due to their area) are
>more like 5/8 wave electrically. The high angle skywave produced bounces 
>right
>back to earth and cancells out the groundwave. We calculated that if they
>removed about 50 feet from the tower, this problem would likely 
>disappear. Of
>course, the daytime signal would suffer due to the drop in tower gain 
>(1/2 vs
>5/8 wave).

WEEI is a Class B.

It's FCC data is noted:

ELEC HGT IS AVG DUE TO EFFECT OF MUTUAL IMPEDANCE ON CURRENT DISTROBUTION.

Those 207 degree towers are definitely out-sized. If infinitely thin, 
removing 25 feet should do it. Given the face dimensions, removing 
something like 50 feet would indeed be best.

If all it was concerned about was day signal, say a couple of hours after 
LSR to a couple of hours before LSS, then 5/8 wave, 225 degrees, would be 
fine, as it has the optimum H-field, about 425 mV/m/kW at 1 km.

However, if overall performance is considered, 5/9 wave, 200 degrees, is 
better, as this produces little fading, while its H-field is still very 
good, at about 405 mV/m/kW at 1 km.

(Of course, I am talking electrical height here).

It is a big mistake for a high-powered station to install too tall a 
radiator, whereas it is a significant benefit for a low-powered station, 
especially a Class C.

For Class As and high-powered Class Bs, such as WEEI, it is best to stay 
200 degrees or under.

It is also bad news for a Class A to use too short a tower or towers.

KGO uses 90 degree towers, and the close-in fading observed on the other 
side of the San Andreas Fault is significant.

I am less than 50 miles from the KGO Tx site, and I am on the opposite 
side of the fault, yet even though I am in KGO's 150 kW main lobe towards 
the SSE, I also receive considerable high angle radiation from those 
exceptionally sort towers, thereby causing fading irrespective of the 150 
kW groundwave, which seems to have trouble punching through the fault.

KGO has a salt water path to each of the principal cities it purports to 
serve: S.F., San Jose, and Oakland. KSO's skywave is pretty impressive, 
too ... Alaska to Mexico, as Ray Taliaferro was formerly fond of saying. 
However, the close-in fading is significant.

Definitely an antenna system done "on the cheap".