Picking up a radio station

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  #1  
Old 01-17-15, 04:53 AM
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Picking up a radio station

I need some electrical advice from the brain trust.

One of my customers has added a new building onto an older section. The facility is near the transmitting tower array of a very powerful AM radio station. The complaint is that the radio station is bleeding into the intercom portion of one of our systems. Our site visit showed that the radio station is also present in the telephones, on television speakers, and (quietly) in the overhead paging speakers. An inductance wand placed near any electrical outlets, light switches, or even some appliances reveals the radio station. I tried all the "normal" fixes to treat the symptoms -- grounding unused pairs in the mults, grounding shields at both ends, adding capacitors to the audio paths. Nothing helps.

None of this happens in the older section of the facility, which is actually closer to the transmitters. It is also intermittent, and could be months between calls.

It has been very cold lately (single digits) and the ground is frozen. I'm trying to see if there is a pattern of dry weather that coincides with past service calls, thinking that perhaps low humidity is reducing ground rod efficiency.

In the meantime, any ideas are welcomed.
 
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Old 01-17-15, 05:19 AM
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I suppose a Faraday cage around the whole building is a bit impractical.
 
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Old 01-17-15, 05:28 AM
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Here, a radio transmitter license requires it's holder to not adversely affect any other system.
One call to our federal communication office would have a quick visit by the air wave police.

My parents were neighbors to a ham operator in our home city and anytime his high power transmissions affected their electronics a quick call to the communications office would end his evening.
Even an arcing pole top power transformer that affected AM radio would be quickly changed by the power company.

Do these regs exist in the US?
 
  #4  
Old 01-17-15, 07:35 AM
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This high power is overloading existing electronic circuits. It is highly unlikely the broadcaster is transmitting signals out of band that are out of spec. You are facing an exercise using ferrite based snap on chokes. Fair-Rite Catalog |

These chokes will be placed near the intercom amplifier, television, and each telephone. Are the telephones analog or digital? For instance, the intercom wire driving the speakers (70volt line, etc) will leave the intercom amp and within a foot of the amp, use a snap on choke from above. Using several turns has great benefit. Do not bother putting on chokes at the speaker, it's the amp that is being affected. Don't forget the mic inputs, that is likely the best path in for the culprit signal. THis will take work..
 
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Old 01-17-15, 08:16 AM
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It has been a long time, but I would want to know the transmitting limitations of that station and then request a field strength mapping of your area to confirm they are within regulations. They have the meters and they should be happy to cooperate or as Greg suggested the FCC will be willing to do the same.

Being intermittent and affecting the new building and not the old is curious, but I suspect it is affecting the old to some degree since you have detected it with multiple electronics.

Have you talked to the radio station?

Bud
 
  #6  
Old 01-17-15, 09:12 AM
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Here, a radio transmitter license requires it's holder to not adversely affect any other system.
One call to our federal communication office would have a quick visit by the air wave police.

My parents were neighbors to a ham operator in our home city and anytime his high power transmissions affected their electronics a quick call to the communications office would end his evening.
Even an arcing pole top power transformer that affected AM radio would be quickly changed by the power company.

Do these regs exist in the US?

Read more: http://www.doityourself.com/forum/el...#ixzz3P6E9YwQD
That is not how it works in the USA. A broadcaster owns a station license that gives them the "right" to transmit. They do need to maintain the transmitter to legal specs, regarding power and spurious emissions. The antenna system is also subject to approval. The broadcaster is not legally responsible to fix any and all susceptable equipment in the area. If the broadcaster is "clean", then the owners of affected equipment are at least legally on their own to mitigate the interference. The EU is a bit ahead of the US in regards to immunity specs and laws on both commercial and residential immunity. Unfortunately, if the equipment does not have a CE mark, then it is very likely not tested and equipped to deal with high power RF fields.
 
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Old 01-17-15, 09:15 AM
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It has been very cold lately (single digits) and the ground is frozen. I'm trying to see if there is a pattern of dry weather that coincides with past service calls, thinking that perhaps low humidity is reducing ground rod efficiency.
I am not an electronics guy and a lot of this is over my head, but I do think it might be reasonable to check the resistance to ground at the ground rod. It could be that possibly as many as 2 or 3 rods may help.
 
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Old 01-17-15, 10:41 AM
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Telecom Guy is right. I work in a TV station, within a building that houses three radio stations. We had the same trouble with our studio intercom system, and the phones. Ferrite chokes removed MOST of the country music from our systems. Good luck!
Andy
 
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Old 01-17-15, 11:10 AM
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Ferrite chokes can be used as well as a handful of capacitors. Capacitors can be added from the affected lines to ground to bleed off the signal.

I have customers directly next to WABC's 50Kw 770 AM transmitter site in Lodi, NJ. I had the stations audio on the phone system, the intercom, even thru the backup fire alarm transmitter. I added some mylar and disc caps to ground. The idea is to find the highest possible capacitance that will work and not affect the audio.
 
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Old 01-29-15, 05:42 AM
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Thank you for the suggestions. Got sidetracked by the flu and another customer whose emergency call took precedence. I'm going to post that as a new FYI thread.

Anyways, an electrical contractor found a severely corroded main ground buss in the new section of the building. Its location made it appear as if the installers were trying to hide it. They are going to replace it.
 
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Old 02-01-15, 04:17 AM
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Cool

As a radio broadcast engineer for more then 10 years I can offer this bit of advice. On occasion we would receive phone calls from neighbors in the area describing this problem (AM radio station was interfering with the telephone) and asked what could be done. We kept a stock of filters on hand and would offer to provide them for free to the affected residences. We never had an issue/complaint beyond that.

Yes, an AM broadcast transmitter likes to get into EVERYTHING! Transmitter was located about 500 feet from the building and I remember being able to hold the input wire on cheap sets of computer speakers with my bare hands and the station would start playing out of the speakers. Very reputable group of stations and we performed yearly field strength/spectrum analysis of the stations.

A phone call to the engineering department of the radio station may very well produce good results for a quick and easy way to obtain the filters.

Good luck with it and let us know what the outcome is.

Cheers!
 
  #12  
Old 02-01-15, 06:15 AM
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If the old building has wire lath stucco on the outside, or is covered in metal siding, that is probably why they don't have trouble there. Perhaps armored electrical cables was used as well.
 
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Old 02-01-15, 12:43 PM
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Thanks for the replies. I will post back when I hear something.
 
  #14  
Old 02-01-15, 01:27 PM
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Ferrite chokes removed MOST of the country music from our systems
How indiscriminately sad!

IIRC, Lucille Ball made claims once that she could hear radio transmissions through her dental work.
 
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Old 02-01-15, 01:48 PM
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Back before the FCC put caps on the power, WLW in Cincinnati, with their transmitter at the VOA site north of the city, was truly "the nation's station". People complained the station came in through their dental fillings, fence wire, various kitchen utensils, etc. It wasn't long before the friendly candy company made them throttle down to 50 kw.
 
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Old 02-01-15, 02:20 PM
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I remember picking up WCKY in Cincinnati when I was a kid messing around with carbon tube radios.......in Georgia!
 
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Old 02-01-15, 08:54 PM
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Reminds me when a date would think it was time to get home. I would punch up WWL New Orleans on the car radio which was on central time. See honey, it's only 11:45/. LOL
 
  #18  
Old 02-02-15, 08:00 AM
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In southern Indiana, late 40s or early 50s, my parents could easily get Big Band music on radio in the evenings, wonderful rich sound, from New Orleans (broadcast from a hotel?).
 
  #19  
Old 02-02-15, 11:05 AM
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solar wind; the reason why your parents COULD NOT get the music during the day!

from wiki:
The Kennelly–Heaviside layer, named after Arthur E. Kennelly and Oliver Heaviside, also known as the E region or simply the Heaviside layer, is a layer of ionised gas occurring between roughly 90–150 km (56–93 mi) above the ground — one of several layers in the Earth's ionosphere. It reflects medium-frequency radio waves, and because of this reflection, radio waves can be propagated beyond the horizon.

Propagation is affected by time of day. During the daytime the solar wind presses this layer closer to the Earth, thereby limiting how far it can reflect radio waves. Conversely, on the night (lee) side of the Earth, the solar wind drags the ionosphere further away, thereby greatly increasing the range which radio waves can travel by reflection, called skywave. The extent of the effect is further influenced by the season, and the amount of sunspot activity
 
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Old 02-02-15, 02:14 PM
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So that explains it While big game hunting out past Rifle, Colorado, we tried listening to the World Series. Could only pick it up on AM, since FM was more line of sight at that location. Even with the AM, since it was modulating like a sine wave, we had to change stations every few minutes to have continuity of the game.
 
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