Blaw-Knox tower in Ireland

[K5WLF]

I just got back from 3 weeks in Ireland. While we were coming back to Donegal from Cork, I happened to see a B-K tower along the motorway near Belfast in NI. I fired off a couple of quick shots and luckily, considering we were running about 90 MPH, managed to get usable (although not portrait quality) images, herewith attached. Turns out that particular tower was the only Blaw-Knox the BBC ever used, because they figured out that it wasn't the magical radiator that B-K touted it as. Pretty good story about it at the following URL:

http://www.bbceng.info/Install/Transmitter%20Projects/Reminiscences/Lisnagarvey/Lisnagarvey_Blaw-Knox.htm

Sure wish I could have brought some of that cool Irish WX back here to Texas.

ldb

[K5WLF]

Weird, one of the pics posted twice. Must have brought Murphy back with me.

[KA3ZLR]

Hi,

Hey How was Belfast things OK there Stable..? I have Family in Ireland.


73
Jack
KA3ZLR

[flintstone mop]

looks like the "half brother" to the WLW Blaw Knox tower.

[k4kyv]

Looks like the top section got lopped off - explained in the linked article.

There's one somewhere in the US that has only the bottom half still standing, used as a platform for multiple communications antennas. The BC station moved their transmitter site to another location.

The B-K towers were never touted to be magical radiators. The geometrical design was supposedly for structural reasons, and normally only one section of guys was used at the mid point. That is strictly an urban legend that the bulge in the middle was to accommodate higher rf current. The electrical difference between a diamond shaped and a uniform cross-section tower of the same height is inconsequential.

I read somewhere there are one or two more B-Ks in the British Isles, somewhere in Northern England and/or Scotland, although the article says this is the only one. There are also a  couple in Central  and Eastern Europe. A very large one reportedly stood in northwestern France, but was destroyed during WWII.

[W4AAB]

In the BBC article, there was a mention near the bottom of the article page of the other Blaw-Knox towers. I have PLENTY of pictures of the WSM tower. It sure helped when they put the exit in at mile marker 71 on I-65 back in the late 1980's where you could drive right by it. The first picture K5WLF sent shows a three-wire radiator coming off the top of the tower. We need some cool WX here, too.

[k4kyv]

The first picture K5WLF sent shows a three-wire radiator coming off the top of the tower.

I don't see anything in the first photo.  Are you talking about the photo in the BBC article? That one shows a tubular mast at the top of the tower, with what looks like a capacity-hat on top of the mast. They must have gone to a substantially higher  frequency to take down the top hat, mast and that much of the tower itself.



Look at the guy wires in the photo.  They must not have shown up in the original photo, and someone did a poor job of hand-drawing them in.  It looks like each guy level has only two guy wires per set.  The ones at WSM and WLW each have eight guy wires at the mid-section with none at the top.

They must have hand-drawn the top-hat as well.  You can see they got the perspective wrong, or else the circular part was tilted at about a 45° angle.

The one at WSM  had about 80 ft. of the mast cut off some time in the late 30s, to get rid of a high angle lobe that was causing severe fading in Chattanooga. The mast was given to a high school, which used it for a flag pole until just a few years ago. The remnant of the mast now carries an abandoned FM antenna that was used when the station first began an FM service.  I think they sold the FM, which now operates under a different call sign at a different location.

Here is an interesting titbit of history that links Blaw-Knox to a name that rings familiar to-day:

The Blaw-Knox Company name was adopted July 6, 1917, marking the merger of Blaw Steel Construction Company with the Knox Pressed and Welded Steel Company. This merger introduced the company to the steel industry and also brought together the three Lehman Brothers into one business firm.

http://hawkins.pair.com/blaw-knox.html

[K5WLF]

Hi,

Hey How was Belfast things OK there Stable..? I have Family in Ireland.


73
Jack
KA3ZLR

We never got into Belfast this trip, Jack. I go to visit a friend in Donegal and we spent a couple days in the Connemara and a day in Cork at Blackrock Castle Observatory (pictured). I was talking to a guy from Belfast at the hotel in Cleggan and he said that things were pretty quiet there now. However, he said that while Derry will probably eventually settle into a permanently stable situation, he doesn't hold the same hope for Belfast. He thinks the old animosities are too deeply rooted and that there will always be some problems there because of that. He also hopes he's wrong, and that folks in Belfast will overcome the past.

73
ldb

[k4kyv]

However, he said that while Derry will probably eventually settle into a permanently stable situation, he doesn't hold the same hope for Belfast. He thinks the old animosities are too deeply rooted and that there will always be some problems there because of that. He also hopes he's wrong, and that folks in Belfast will overcome the past.

Some people are still trying to fight our civil war.

[KB5MD]

I was in Dublin last week and the 50-70 degree weather there is certainly to be chosen over the 100+ temps here in South Arkansas. 

[WU2D]

Family vacation to London last month about a week before the riot fun and all I can say is I am glad that we brought our sweatshirts and heavy rain gear. I an always amazed at the UK weather. Imagine our surprise when we got off the plane in Boston to 100 degrees. My 18 year old spent a week drinking Guinness and not being carded - in fact I never saw anybody get carded - different world.

Mike WU2D

[k4kyv]

My 18 year old spent a week drinking Guinness and not being carded - in fact I never saw anybody get carded - different world.

But we live in the land of the free. 

Common sense isn't as extinct over there as it is here. A few months ago in Chattanooga, they carded me (at age 68) before they would serve me at a restaurant, then the server called the manager out because my DL doesn't have my picture on it.

Like any damn fool with bat-sense couldn't tell that I am old enough to order a beer.

[W2DU]

Hi Don, I quote from your previous post: "The electrical difference between a diamond shaped and a uniform cross-section tower of the same height is inconsequential."

Sorry Don, but I must respectfully disagree. In the late 30's WIP in Philly was using a Blaw-Knox, and discovered their radiation pattern wasn't what it should have been. So the CE of WIP contacted RCA, and especially George Brown, to investigate. Brown then built a scale model of the WIP tower and made pattern measurements, the results of which did not conform to what was expected. Brown reasoned that it was the non-conforming shape that distorted the current structure on the tower. Additional pattern measurements of the actual WIP tower were taken via helicopter that verified the error caused by the irregular shape of the tower.

As a result of Brown's findings the FCC made the ruling that new BC installations, and older BC stations requesting a change of antenna, that all towers from then on must be of uniform cross section. It has been found that towers of uniform cross section radiate the pattern expected from that shape of tower.

Walt

[k4kyv]

As a result of Brown's findings the FCC made the ruling that new BC installations, and older BC stations requesting a change of antenna, that all towers from then on must be of uniform cross section. It has been found that towers of uniform cross section radiate the pattern expected from that shape of tower.

Walt

They must allow at least some exceptions, unless that ruling went into effect sometime after the mid 60s. A local station here was built in the 60s; they used a self-supporting tower that was shaped a little like the Eiffel Tower, wider at the base and tapered off at the top. Years later they replaced it with a much taller guyed tower, uniform cross section.

WBT lost two of their three B-K towers in hurricane Hugo. Instead of replacing them with new uniform cross-sectional towers, they rebuilt the B-K diamonds per blueprints they had on file.  I'm sure new off-the-shelf  uniform CS tower stock would have cost a lot less, but they preferred to rebuild the old ones. The FCC must have granted a waiver and grandfathered the old tower design.

I'll have to  check out that article. I think I have it in one of the issues of IRE Proceedings. I  seem to recall  that the diamond shape was used for structural, not electrical reasons. B-K was accused by competitors of using the design as a sales gimmick, because of the attention attracted by the unique shape. B-K also made some 4-sided uniform cross-sectional towers of the cantilever design, with only one set of guys at the mid point, just like the diamonds.

Maybe the diamond shape was why they miscalculated the length of the WSM tower and had to shorten it. I was told by someone who knew the former engineer at WSM that erroneous velocity factor figures were used in the original design.

Something that has always puzzled me about the cantilever design is how they handle wind shear. It is not uncommon for wind velocity to be substantially different (both in speed and direction) several hundred feet up in the air than it is at ground level. It would seem that with only that one set of guys, if there was a strong wind at upper elevations, but the wind was calm or blowing in a different direction at ground level, the guy point at the mid section of the tower would act as a  pivot and exert a side thrust to the base insulator. Those big ceramic base insulators are designed to withstand compression, but become very brittle in the presence of sideways shear stress. This would be especially true with the double stacked base insulators commonly used with large AM towers at the 50kW+ level. A second set of guys would tend to maintain the tower rigidly vertical and eliminate or greatly reduce this stress on the insulator in the presence of a non-uniform lateral force along the length of the tower. I have noticed that a few of the B-K diamonds have a second set of guys added to the top of the tower, but WSM and WLW have been standing for almost 80 years with only the one set of guys.