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Author Topic: What do the commercial radio stations use for an antenna?  (Read 42303 times)

K0OD

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RE: What do the commercial radio stations use for an antenna?
« Reply #15 on: December 14, 2017, 09:05:38 AM »

Quote
Historically any effort to produce an electrically short AM antenna resulted in an impedance characterized with a low resistance and high reactance yielding a commensurate narrow audio bandwidth

Could the bandwidth of an AM broadcast antenna be so narrow as to affect the quality of  the transmitted audio? I wouldn't think so.
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K5TED

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RE: What do the commercial radio stations use for an antenna?
« Reply #16 on: December 14, 2017, 10:55:42 AM »

Quote
Historically any effort to produce an electrically short AM antenna resulted in an impedance characterized with a low resistance and high reactance yielding a commensurate narrow audio bandwidth

Could the bandwidth of an AM broadcast antenna be so narrow as to affect the quality of  the transmitted audio? I wouldn't think so.

Yes, it can
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KM1H

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RE: What do the commercial radio stations use for an antenna?
« Reply #17 on: December 14, 2017, 05:20:46 PM »

Quote
Could the bandwidth of an AM broadcast antenna be so narrow as to affect the quality of  the transmitted audio? I wouldn't think so.

Absolutely it can and it really gets critical at the low end where even 1/4 wave is huge. Short antennas and high Q tuning networks can restrict the bandwidth.

Carl
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KB2IUA

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RE: What do the commercial radio stations use for an antenna?
« Reply #18 on: December 15, 2017, 03:38:09 AM »

Could the bandwidth of an AM broadcast antenna be so narrow as to affect the quality of  the transmitted audio? I wouldn't think so.[/color]

Yes! remember the bandwidth of s good AM signal is 4 to 5 times that of a ham radio SSB signal. The transmitter may see 50 ohms 0 reactance at the carrier frequency but be dealing with something much different 4000 Hz on either side.[/color]
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K0OD

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RE: What do the commercial radio stations use for an antenna?
« Reply #19 on: December 15, 2017, 06:50:14 AM »

I don't recall old-time hams mentioning audio distortion on 160-m AM with narrow mobile antennas. What about the rare use of sideband on 630 nowadays? How about NDBs that use MCW with ludicrously short antennas down to 190 kHz?

Learning something here. 
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AA2UK

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RE: What do the commercial radio stations use for an antenna?
« Reply #20 on: December 15, 2017, 09:08:19 AM »

It results in an AM broadcast station sounding like it has phase distortion to the listener. You'd probably never notice it on a 160 meter AM ham station. There's really no AM operation on 630 meters.
Have a look at this document, http://www.nrscstandards.org/documentarchive/nrsc-g100.pdf
Maybe I'm wrong.
Bill, AA2UK  
« Last Edit: December 15, 2017, 09:11:02 AM by AA2UK »
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KM1H

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RE: What do the commercial radio stations use for an antenna?
« Reply #21 on: December 16, 2017, 01:53:50 PM »

Quote
I don't recall old-time hams mentioning audio distortion on 160-m AM with narrow mobile antennas

A mobile whip on 160 is highly inefficient which broadens the BW and any matching network was quite rudimentary, QSY was rarely used once tuned up on a group frequency. Plus audio was restricted by the WW2 surplus carbon mikes most used. I used to work a lot of the 160 commuters with a Viking I and JT-30 mike in the late 50' and also on 11M even after we lost it ;D ::).

Carl
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WB4TJH

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RE: What do the commercial radio stations use for an antenna?
« Reply #22 on: December 19, 2017, 02:16:28 PM »

I worked for a Memphis TV station for over 20 years and we also had an AM broadcast station. The actual antenna was a tower several hundred feet all. It had several hundred pounds of copper in each of four deep wells for a ground system. Many AMers will used  four phased tower/antennas for directivity. The engineers would actually work on antenna/tower while it was energized. They said once you were on the tower, there was no RF sensation, they only got buzzed when getting on or off the tower.
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AD4U

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RE: What do the commercial radio stations use for an antenna?
« Reply #23 on: December 27, 2017, 05:54:23 AM »

Another good "read" is to google WAPE radio on 690 KHz in Jacksonville FL. Back in the 1960's and later the Big APE would cover the coast from Miami FL up to Va and maybe further north during the day with a very strong signal. They used an ape call like Tarzan did. I grew listening to the BIG APE in the daytime and WABC in New York with Cousin Brucie at night. This was the golden age of AM broadcast.

Dick AD4U
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KD0REQ

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RE: What do the commercial radio stations use for an antenna?
« Reply #24 on: December 28, 2017, 07:35:16 AM »

I believe the commercial AM radio band starts a 530 KHz. I was wondering what they use for an antenna.

What kind of loading coil do us use for a clear channel 50,000 watt signal?


they radiate from the tower. the whole tower is the antenna.  towers are generally isolated on large insulators to the pad, and a lightning ring is mounted on one or more legs of the tower to ground. the lightning ring is two rings, one to the tower, the other at a 90 degree mounting inside and centered in the first goes to ground.

if there are directional requirements at night for the signal, there are additional similar towers and a phasing network located before the primary tower, with coils and capacitors to split the power and generate a directional signal. the details are worked out by consulting engineers generally based in the VA swamp.

AM transmitters do have internal matching networks of appropriate size so they can dial down the SWR to a match. 

in olden days, when electrons were rationed, there were all sort and manner of dipoles and zepps used for transmitting on the common 200 meter frequency the Commerce Department had everybody share.
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KM1H

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RE: What do the commercial radio stations use for an antenna?
« Reply #25 on: December 29, 2017, 03:20:59 PM »

The WBZ remote station in Springfield MA, WBZA, was a Westinghouse company and had a pair of self supporting towers on the Westinghouse roof with a single wire feed to a flatop antenna. This was in 1922.

I was at the tower and building demolition party a few years ago when an AM Special Event ham station, W1Z, was using a quick replacement antenna a bit up the towers and it was all filmed for posterity. The old copper was stolen long before that :o

http://www.springfieldradio.com/

The MGM Casino bid failed and this is the latest proposal

http://www.telegram.com/article/20150904/NEWS/150909491

Carl

 
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W4KYR

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RE: What do the commercial radio stations use for an antenna?
« Reply #26 on: December 29, 2017, 05:59:08 PM »

I believe the commercial AM radio band starts a 530 KHz. I was wondering what they use for an antenna.

What kind of loading coil do us use for a clear channel 50,000 watt signal?


they radiate from the tower. the whole tower is the antenna.  towers are generally isolated on large insulators to the pad, and a lightning ring is mounted on one or more legs of the tower to ground. the lightning ring is two rings, one to the tower, the other at a 90 degree mounting inside and centered in the first goes to ground.



Like this ?


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WB6BYU

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    • Practical Antennas
RE: What do the commercial radio stations use for an antenna?
« Reply #27 on: December 30, 2017, 07:21:25 AM »

That's a tower lighting transformer - it acts as an insulator for RF while
coupling AC power up the tower for the aircraft warning lights.

WD4HXG

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RE: What do the commercial radio stations use for an antenna?
« Reply #28 on: June 18, 2018, 10:22:25 AM »

That's a tower lighting transformer - it acts as an insulator for RF while
coupling AC power up the tower for the aircraft warning lights.

The shelter for the matching network at the base of the tower was called ‘The Doghouse’. The towers for the 5KW day and 1 KW night station I worked were insulated from earth on a sphere of glass. I always wanted one of the big basket ball size glass insulators. As mentioned the transformer shown was built to provide AC Power for tower lighting. The large spacing was used to prevent the RF from arcing. In the station where I worked the coax from the phasing network for day-night pattern was made from 8 inch diameter copper tubing used as the outer conductor. The center conductor was spark plug wire. It was made by Delco and sold by auto parts houses for use in vehicles which did not use resistive center conductor for spark suppression noise. When the tubing was sealed it was kept at a positive pressure. Both towers were driven. The guy wires used insulators along the length to keep the guys from forming resonant sections and distorting the radiation pattern. When climbing the tower you placed a ladder against the wooden dog house at the base of the tower. Standing on the roof of the dog house you could jump from the roof to the tower, grasp it with your hands and stabilize your feet on the rungs. That way you avoided shock. Alternatively you had a stooge kill the RF output and started to climb from the ground. Once a few feet above ground you hollered for the stooge to turn the RF back on and went about your work. Due to the insulator at the base it was easier to get on from the Dog House. The ground system was a ring of copper tubing about 20 feet in circumference. Bare # 8 copper wire on a spool mounted on a tractor rear lift was attached to the copper ring. A plow opened a furrow as you drove the tractor from the tower, a press pushed the wire deep into the furrow and a trailing plow rolled the dirt back over the wire. We used 126 radials. As the towers were built in a swamp the radials were replaced every three to four years. The station owner whined like a snow tire on ice each time we planted copper wire because of the cost. I can only imagine what he would do today. Each radial was just over 200 feet.
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K5WLR

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RE: What do the commercial radio stations use for an antenna?
« Reply #29 on: June 19, 2018, 09:39:16 AM »

Another good "read" is to google WAPE radio on 690 KHz in Jacksonville FL. Back in the 1960's and later the Big APE would cover the coast from Miami FL up to Va and maybe further north during the day with a very strong signal. They used an ape call like Tarzan did. I grew listening to the BIG APE in the daytime and WABC in New York with Cousin Brucie at night. This was the golden age of AM broadcast.

Dick AD4U

Wow, WAPE... that brought back some old memories of when I was stationed at Myrtle Beach AFB, SC in the early 70s. As I remember, the station was in Jacksonville, FL and I got it clearly during the daytime. Once the sun set, it was gone... went directional and/or lowered power, I guess. They gave me a connection to home... I maintained my residence in Florida then....

Thanks for the memories, Dick!  :)

Will Rogers
K5WLR
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