Slanted Antennas on Buildings

[N9PUR]

I see these slanted antennas (photo attached) on quite a few commercial buildings built prior to the early 1990's in the area. From the information I've gathered, these antennas were used to receive Muzak which was broadcast on sub-carriers of commercial FM radio stations until the mid-1990's. The antenna slant would make sense due to the polarization of most commercial FM transmissions. Muzak is now distributed via satellite and over the Internet. Can anyone confirm this information, and if that's the case, I'm curious if anyone knows which FM station in Indianapolis the sub-carrier used to be broadcast on.

 

[N9IIT]

I believe the Muzak was carried over WTPI-107.9 FM. I was also told it was carried over WFYI 90.1 but that doesn't seem correct with a for-profit entity being carried over NPR airwaves.

 

[AK9R]

WFYI 90.1 had SCA information on their subcarrier, but I believe it was newspapers for the blind.

As for a public radio station being involved in a commercial enterprise, at one time WFYI had the best satellite uplink station in town. During the Indy 500, WFYI would uplink both the ABC feed and the international feed. Of course, WFYI charged for this service and those uplink deals were just another part of their revenue stream.

 

[N9PUR]

This is some good info. I was interested in radio communications when I was much younger, and remember seeing these antennas on just about any building that played the Muzak "elevator music". The Laughner's Cafeteria, Clancy's, Hardee's, McDonald's, Kroger, and Marsh in Plainfield back in the 1980's - early 1990's all had these antennas, and I figured the antennas had something to do with the background music since you never saw one of these antennas on a house, and no one knew what they were for. The elementary school I attended in Plainfield had one of these antennas as well, but I remember one of the custodians told me it was the antenna for the AM/FM radio that was part of the building intercom system since they could not receive a strong FM signal inside the building.

 

[kruser]

Why the slant? Did they use some odd polarization at the transmitter?

I recall trying to get rid of LSM from an 800 MHz site not far away.
I had a 12 element yagi but the signal hitting the radio was bad as it was from two simulcast sites.
I was about to give up when I decided to try turning the yagi on its side. That resulted in not enough signal so I tried 45 degrees. It worked!
It allowed just enough signal from one site but blocked the other.

 

[KB7MIB]

Back in the 90's, I could receive Muzak or something similar on a pair of 900 MHz frequencies in the metro Phoenix area. They were somewhere between 940-956 MHz IIRC.
So SCA on an FM broadcast station, or a satellite feed, weren't the only methods of distributing the music.

John
Peoria, AZ

 

[kb5udf]

Slanted Antenna

Ok I'll bite. I suspect its to reduce loss due to polarization mismatch.
I did a little research b/c I thought FM broadcast 88-108 was always horizontal polarization. I was wrong. Orginally, it was horizontal only, but later, other options crept in. The synopsis of my reading and and best guess
is that by rotating the horizontal antenna 45 degrees, they suffer less polarization loss for something that
is other than horizontal. One article said the loss would be as little as 3db.

Regarding the 900mhz radio you heard, that may have been a radio station studio to transmitter link.


Regards,

JB

 

[nd5y]

Mounting an antenna at 45 degrees like that (or vertical or horizontal) will have absolutely no effect if the transmitted signal is circular polarized as nearly all FM stations are. That's one reason why they use circular polarization.

I have never seen one of those antennas mounted like that. They were always vertical or horizontal.

 

[AK9R]

In the beginning, FM receiver antennas were similar to TV antennas and were horizontally polarized. Then, FM car radios became popular, but their antennas are always vertically polarized. So, the FM broadcasters compromised and used circular polarization so they would reach the largest market of listeners.

As for the Muzak and other receive-only FM services using antennas mounted at 45 degrees, this was a very common practice around Indiana.

 

[KK4JUG]

Back in the late 60s, I worked for an FM station in Montgomery that had a sub-carrier for background music. After my air shift, I helped install the systems at businesses and we used "TV-type" antennae.

That was the first time I ever saw 16 2/3 rpm records The fidelity was marginal at best but, hey, it was elevator music.

 

[DJ11DLN]

Cool info. I remember seeing those antennas around on different businesses and wondering what they were for. The few times I asked about them nobody seemed to know. Or maybe they just thought I was being nosy and were too polite to tell me to get lost.:roll:

 

[KK4JUG]

Cool info. I remember seeing those antennas around on different businesses and wondering what they were for. The few times I asked about them nobody seemed to know. Or maybe they just thought I was being nosy and were too polite to tell me to get lost.:roll:

I suspect most of them didn't have a clue as to how it was done. They just wanted the music.

Hidden in a closet somewhere was a vented black box that had the receiver and an amplifier for the low-voltage speakers. It didn't have the radio station's call letters on it. Rather, it had the parent company for the radio station's name. If I remember correctly, the volume pot needed an star wrench and everything else was inside and out of sight.

 

[krokus]

Why the slant? Did they use some odd polarization at the transmitter?

FM broadcast stations use circular polarization to minimize the differences between the automotive antennas (vertical) and the building antennas (horizontal).

The Muzak antennas might have been to visually identify their antennas. (Just a theory.)

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