Poor FM reception when it is Raining

FM does it with frequency!
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Ingebar
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Poor FM reception when it is Raining

Post by Ingebar » Thu Dec 22, 2016 7:18 am

Hello everyone, Thanks in advance for reading this and posting your thoughts.

I'm located in a city with several mountains and coverage is not easy. There are a lot of new buildings too in the area.

Right where the studios are located I don't get a good reception, I placed an antenna outside the building to improve the reception, and it got better. The issue is, when it starts to rain, It's like the antenna is gone.

I already checked that it is properly covered with tape and silicone, so connections are not getting wet.

Does anyone have an oppinion on this.

Thanks again!!

TPT
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Re: Poor FM reception when it is Raining

Post by TPT » Thu Dec 22, 2016 8:12 am

Couple of possible explanations. Remember that the wavelengths at FM frequencies are only about 9 feet long. Hence FM signals can be deflected or channeled by a variety of natural phenomenon. As a result, the FM signal strength in a given area can vary considerably day to day and hour to hour.

Most likely on distant signals is "ducting"---during fair weather the air settles into layers, based on temperature. For example, we'll get a bubble of cold air pushing under warmer air when a high moves in and stops. The boundary between the two different temperature air bubbles acts like a duct--causing FM signals to travel much farther than normal. This effect may last just a morning, until the sun warms the air up & cause it to mix, or several days. Like those cold weather high pressure systems that move in and sit, freezing everyone to the core.

Rainy weather and wind stirs and mixes the air, eliminating these temperature differences. Also, when the leaves are out, the wet leaves can absorb signals, so there is less signal to reach your antenna from distant stations.

Ingebar
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Re: Poor FM reception when it is Raining

Post by Ingebar » Thu Dec 22, 2016 8:31 am

Thanks for taking the time to answer.

Any possible solution to improve my reception?

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Deep Thought
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Re: Poor FM reception when it is Raining

Post by Deep Thought » Thu Dec 22, 2016 8:37 am

How far away is the transmitter site, and what power are you transmitting with? As noted by TPT, rain can make a marginal reception scenario into a really bad one.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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KPJL FM
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Re: Poor FM reception when it is Raining

Post by KPJL FM » Tue Dec 27, 2016 8:34 am

That's because FM listened to it's Mother when growing up.
FM goes inside when it's raining out.
:roll: your turn, Fossil.

Seriously, there may be an unintentional re-radiator or director element nearby, that gets affected by the weather.
Trim to fit, paint to match, tune for minimum smoke.

Ingebar
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Re: Poor FM reception when it is Raining

Post by Ingebar » Tue Dec 27, 2016 10:38 am

Thanks for answering guys.

The distance would be arund 6 miles, and the total radiated power is 15KW.

I used to have a clear view of the transmitters site before, but now there are some new buildings in the way. Anyways, when it is a clear day we get a good reception, but when it rains we get a lot of noise.

Thank you very much.

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Deep Thought
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Re: Poor FM reception when it is Raining

Post by Deep Thought » Tue Dec 27, 2016 12:10 pm

15 KW ERP at 6 miles should burn through just about anything. Do you have a lot of noise on other stations at the same receive point? Could be as simple as a defective nearby power line insulator arcing when it gets wet.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

TPT
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Re: Poor FM reception when it is Raining

Post by TPT » Tue Dec 27, 2016 2:16 pm

I've also heard problems created by a poorly shielded computer in the same building (multi-tenant office building). Especially around 100 mhz. Rain be the clue here--possible cut coax and water getting in to it?

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