WTVN directional array

[Nightpattern]

Anyone know why the WTVN directional array is such a hodgepodge of antenna styles? There are self supporters and guyed towers mixed together. Plus, the antenna heights vary greatly from west to east. I assumed the two east antennas were so short because of the old Southwest airport...but I could be wrong. It just seems so different from other arrays I've seen.

 

[del_griffith]

I've actually wondered the same myself.

Different styles. Different heights.

Generally, it seems styles and heights are normally the same. Although WBNS-AM's night directional stick is not a Blaw Knox designed tower and is guyed.

Wonder if Savoldi has any original documents in the engineering file that would shed some light.

 

[schmave]

I long have wondered this myself. I didn't know if the taller towers provided the deeper nulls, etc. Trust me — I am no engineer.

 

[K4WRF]

Anyone know why the WTVN directional array is such a hodgepodge of antenna styles? There are self supporters and guyed towers mixed together. Plus, the antenna heights vary greatly from west to east. I assumed the two east antennas were so short because of the old Southwest airport...but I could be wrong. It just seems so different from other arrays I've seen.

Now let me say I have never worked on this specific antenna, but many others over a long time and might be able to venture somewhat of an answer.

Just looking at it, it has one tower that is significantly taller than the others and this appears to be the tower used in the non-directional day-time operation. Being taller, it has better efficiency and this is one possibility, improved day coverage. The other is there seems to exist an FM antenna on this same tower and that would optimize that stations coverage. It is also a guyed tower and might have been a replacement for another tower. An old database shows it being only slightly shorter at one time, of only a few degrees. The eastern most towers are very short for the frequency of 610 kHz only 43.5˚ respectively. Where it could indeed be an airport MVA issue, it is very likely efficiency off-set for the taller tower or necessary to provide a lower field contribution with the shorter heights or, all of the above. There are limits on the amount of average field produced by the total array for this class of operation. If you look at the directional field ratio parameters contributed by each antenna; the taller more efficient tower is the same field contribution as one of the short east towers. Another option is towers of differing heights can be used to precisely control nighttime sky wave interference at different elevations and azimuths towards other stations.

 

[del_griffith]

Anyone know why the WTVN directional array is such a hodgepodge of antenna styles? There are self supporters and guyed towers mixed together. Plus, the antenna heights vary greatly from west to east. I assumed the two east antennas were so short because of the old Southwest airport...but I could be wrong. It just seems so different from other arrays I've seen.

Now let me say I have never worked on this specific antenna, but many others over a long time and might be able to venture somewhat of an answer.

Just looking at it, it has one tower that is significantly taller than the others and this appears to be the tower used in the non-directional day-time operation. Being taller, it has better efficiency and this is one possibility, improved day coverage. The other is there seems to exist an FM antenna on this same tower and that would optimize that stations coverage. It is also a guyed tower and might have been a replacement for another tower. An old database shows it being only slightly shorter at one time, of only a few degrees. The eastern most towers are very short for the frequency of 610 kHz only 43.5˚ respectively. Where it could indeed be an airport MVA issue, it is very likely efficiency off-set for the taller tower or necessary to provide a lower field contribution with the shorter heights or, all of the above. There are limits on the amount of average field produced by the total array for this class of operation. If you look at the directional field ratio parameters contributed by each antenna; the taller more efficient tower is the same field contribution as one of the short east towers. Another option is towers of differing heights can be used to precisely control nighttime sky wave interference at different elevations and azimuths towards other stations.

It’s been a long time since I worked there and I wasn’t on the technical side of things. However from what I can remember, the tallest tower was indeed the daytime tower. It also at the time was home to channel 6 before it moved to Dodridge Street and later the Stimmel Road area and home to what was then WBUK or WTVN-FM and now is Q-FM-96. The height was both for the AM frequency and the TV broadcast height. I also believe that WLVQ maintins a back up antenna on the WTVN tower to this day.

However, I believe tower 6, one of the smallest towers was also used as a backup tower for daytime broadcasting.

But why the remaining 5 towers are all smaller than the main daytime tower was always a mystery to me. It is certainly possible that the old South Columbus airport may have played a role in the tower heights, but maybe not. Also I was never familiar in my limited knowledge of directionals about tower height limiting sky wave interference. That’s interesting, because you seldom see differing heights when seeing tower farms unless the towers were built at different times.

 

[DanStrassberg]

Also I was never familiar in my limited knowledge of directionals about tower height limiting sky wave interference. That’s interesting, because you seldom see differing heights when seeing tower farms unless the towers were built at different times.

I believe that this array was designed by the legendary Carl Smith. It was discussed at some length in a now decades-out-of-print book entitled, IIRC, "Radio Antenna Engineering" by Edmund LaPorte. I have no idea where you might find a copy.

The use of towers of differing heights was indeed an attempt to control high-angle skywave radiation. The strongest protections were to co-channel Class III-A stations in Philadelphia (WIP) and Kansas City (it was WDAF then; I guess it's now KCSP). Adjusting the heights of some towers in a DA to minimize the reflected skywave over a specific range of distances from the transmitting antenna is not unique to WTVN, but WTVN may have been one of the first (maybe THE first) station at which this design approach was applied. The technique does work as long as you don't attempt to obtain too much of a reduction. After all, the ionosphere layer in question (sorry, I've forgotten its designation) does vary in altitude from day to day and hour to hour. As the reflecting layer's altitude varies, the critical angle also varies. As the critical angle varies, the distance from the transmitter site at which the reflected skywave is minimized, varies as well.

As for the top loading of several of WTVN's towers, it is certainly unusual. Two towers have a mere two degrees of top loading and one has just one degree. That's the smallest amount of top loading I have seen at any US station. Leads me to suspect that the top loading was added to tweak the vertical radiation pattern. I'm skeptical that such small changes in the electrical height of the towers could have had a useful effect. The top loading clearly was not added to achieve the class-minimum efficiency because the WTVN more than comfortably meets that requirement.

 

[Nightpattern]

I just knew there was a great technical story behind this array. Thanks Dan!

 

[K4WRF]

Also I was never familiar in my limited knowledge of directionals about tower height limiting sky wave interference. That’s interesting, because you seldom see differing heights when seeing tower farms unless the towers were built at different times.

I believe that this array was designed by the legendary Carl Smith. It was discussed at some length in a now decades-out-of-print book entitled, IIRC, "Radio Antenna Engineering" by Edmund LaPorte. I have no idea where you might find a copy.

The use of towers of differing heights was indeed an attempt to control high-angle skywave radiation. The strongest protections were to co-channel Class III-A stations in Philadelphia (WIP) and Kansas City (it was WDAF then; I guess it's now KCSP). Adjusting the heights of some towers in a DA to minimize the reflected skywave over a specific range of distances from the transmitting antenna is not unique to WTVN, but WTVN may have been one of the first (maybe THE first) station at which this design approach was applied. The technique does work as long as you don't attempt to obtain too much of a reduction. After all, the ionosphere layer in question (sorry, I've forgotten its designation) does vary in altitude from day to day and hour to hour. As the reflecting layer's altitude varies, the critical angle also varies. As the critical angle varies, the distance from the transmitter site at which the reflected skywave is minimized, varies as well.

As for the top loading of several of WTVN's towers, it is certainly unusual. Two towers have a mere two degrees of top loading and one has just one degree. That's the smallest amount of top loading I have seen at any US station. Leads me to suspect that the top loading was added to tweak the vertical radiation pattern. I'm skeptical that such small changes in the electrical height of the towers could have had a useful effect. The top loading clearly was not added to achieve the class-minimum efficiency because the WTVN more than comfortably meets that requirement.

Edmund Laport's Radio Antenna Engineering available on-line at this link:

http://snulbug.mtview.ca.us/books/RadioAntennaEngineering/

 

[TomT]

No big secret on the one tall tower. It used to be used for Channel 6 before they moved near downtown. The FM antenna on it now is 93.3.

 

[Nu_Roo_2]

No big secret on the one tall tower. It used to be used for Channel 6 before they moved near downtown. The FM antenna on it now is 93.3.

Is that the same tower WLVQ was on until they started transmitting from the Twin Rivers stick downtown? Unlike WLZT, they had some center-city signal problems, even on campus. I once mentioned this issue on the phone to one of their early DJ's -- Lee Randall, I believe -- and he ripped into me and said that their signal reached areas where other stations had problems. So there! Of course, he was being defensive because he knew what I was saying was true, even though he wouldn't admit it. And campus was a key target for that format back them. Of course, WLVQ still had no problem knocking off WCOL-FM with Q-FM-96's tight Lee Abrams Superstars AOR approach (though not as tight as in many other markets). But I ramble...

 

[rubberchicken]

According to Fybush, yep 96.3 used to be there:
http://www.fybush.com/sites/2004/site-040226.html
(bear in mind this was written several years ago)