One Antenna versus Two Antennas (NYC vs Chicago)

[Markxxx]

OK in NYC on the old World Trade Center and on the Empire State Building there is only one antenna for transmitting TV/Radio in the city. I see on plans for the new building to replace the old WTC, it will also only have one antenna

But in Chicago, on the Willis (Sears) Tower and John Hancock building, both have two antennas for transmitting TV and Radio (though only two TV stations use JH since the DTV transition).

Is there any reason for this? I mean NYC is such a bigger market. Is there any reason why Chicago buildings needed to have two huge antennas on the Willis Tower and John Hancock buildings, while NYC got by fine with just one antenna.

I assume it isn't a problem since the new World Trade building is being built with only one antenna for broadcasting.

I can sort of see the ESB having one antenna 'cause isn't there a pointed spire on the building?

 

[w9wi]

OK in NYC on the old World Trade Center and on the Empire State Building there is only one antenna for transmitting TV/Radio in the city. I see on plans for the new building to replace the old WTC, it will also only have one antenna

But in Chicago, on the Willis (Sears) Tower and John Hancock building, both have two antennas for transmitting TV and Radio (though only two TV stations use JH since the DTV transition).

Is there any reason for this? I mean NYC is such a bigger market. Is there any reason why Chicago buildings needed to have two huge antennas on the Willis Tower and John Hancock buildings, while NYC got by fine with just one antenna.

...

What you're seeing as an "antenna" is actually a mounting pole. According to the Willis Tower's Wikipedia page, there are at least seven FM antennas and seven TV antennas on the east pole, at least one FM and ten TVs on the west pole. The antennas are inside protective covers, which makes it impossible to see the separate antennas from the ground.

Then, there's "diplexing", where more than one station shares a single antenna.

Point being, the number of poles you see does not necessarily directly relate to the number of transmitting antennas present.

Finally... for technical reasons, you can only put so many stations at a given site, regardless of how large a market it is... Stations have to be at least 800KHz apart, and the FM band is of finite width. Under current FCC regulations, you can have a maximum of 25 full-power FM stations at any given site. Markets far smaller than Chicago are able to support 25 FM stations, but once you reach that 25 mark it doesn't matter how much larger the market is -- you can't have any more stations.

 

[markwooldridge]

To me it would make sense if all the local TV stations would share transmission facilities. Here in Greensboro we have local stations with facilities to the north, south, and west of us that serve our area, and some from east in Raleigh come in nicely. This would simplify reception for a lot of people - a small UHF Yagi pointing in the right direction gets all channels.... sounds simple enough for a consumer rather than fiddling around with a rotator (even in the digital age). The downside is that in some locations they'd get no terrestrial TV at all, and thus translators would be required for that area.

Here's a nice set of pictures that someone took of the Winter Hill transmission facilities that serve a good part of NW England. It's been switched over to digital and it shows the differences between "transition" and "post switchover". This mast carries 6 DTV multiplexes, 8 FM stations and 5 DAB stations. To ensure good coverage, this transmitter has about 50 translators, but the translators only carry 3 DTV multiplexes and some have 4-5 FM stations, and maybe some DAB mixed in.

http://tx.mb21.co.uk/gallery/winterhill/winter-hill11.php

 

[KML0224]

A good example of an omnidirectional market is Hartford/New Haven. I live in New Britain, CT, which is in southern Hartford County. Rattlesnake Mountain is to my northwest (WTXX-DT, WEDH-DT, WVIT-DT and WTIC-DT). Avon Mountain is to my north-northwest (WFSB-DT and WUVN-DT). Madmere Mountain is to my south-southwest (WTNH-DT and WCTX-DT). Lastly, the sites of WEDN-DT Norwich and WHPX-DT of New London are both to my southeast in Bozrah and Montville, respectively. WEDN-DT is a PBS station with identical programming to WEDH-DT of Hartford, so I'm not worried about them.

 

[avtosalon]

But in Chicago, on the Willis (Sears) Tower and John Hancock building, both have two antennas for transmitting TV and Radio (though only two TV stations use JH since the DTV transition).

Actually, the John Hancock Center has six television stations currently on-the-air transmitting from the top (2 full-power / 4 low-power, 4 digital / 2 analog):

4 WOCK-CD (low-power digital, maps 13-1 thru 13-4)
6 WLFM-LP (low-power analog, pretends to be a radio station at FM 87.7)
21 WYCC (full-power digital, maps 20-1 thru 20-3)
33 WCHU-LP (low-power digital, maps 61-1 and 61-2)
38 WGBO-DT (full-power digital, maps 66-1)
41 WOCH-CA (low-power analog)


Willis Tower has total 17 TV stations currently, and Aon Center has one TV station.

 

[Markxxx]

Thanks for the info.

What I still don't get is how come NYC manages to have two buildings WTC and Empire State with only one antenna mast, while Chicago has the two buildings with TWO antenna masts. Why the need for 2 masts?

 

[FreddyE1977]

I can tell none of you fellas have ever sold Tenna-Rotors for a living!

 

[PTBoardOp94]

There's probably no "need" for two masts. Several possible explanations:

a) Aesthetics. Whoever designed the building wanted two poles sticking out. I think this is how the Chase tower in Indianapolis was designed (only one of the masts ever had transmission facilities)

b) Weight. Antennas are heavy. Some structural engineer might have looked at the support structure for John Hancock and decided that it would be better to have two masts to help distribute the weight.

c) Growth over time. I have no idea if this is the case in Chicago, but in some places, TV and radio stations began transmitting from their own masts and later moved to skyscrapers. The original mast may have been designed to carry a certain load, and a second mast was subsequently added at the top of the building.