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Author Topic: how far does fm travel ?  (Read 493 times)

VA07

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how far does fm travel ?
« on: May 26, 2021, 08:07:01 AM »

im a little confused about how far fm travels im in icard nc and can hear a country station out of charottle (its at 103.7 mhz) and im wondering how i can hear that far away the radio im using is a g3 globe traveler
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K6BRN

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Re: how far does fm travel ?
« Reply #1 on: May 26, 2021, 08:39:36 AM »

Commercial FM boadcasts on 87.5 to 108 MHz are generally line of sight communications and normally have a range of 20-100 miles depending on transmitter power and antenna height (which varies widely from station to station).  During some propagation conditions, rare in recent years, atmospheric phenomena can briefly carry the signal much farther.

See this link for more info:

https://en.m.wikipedia.org/wiki/FM_broadcasting

Brian - K6BRN
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KA4DPO

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Re: how far does fm travel ?
« Reply #2 on: May 26, 2021, 08:53:05 AM »

Standard broadcast FM stations can be heard 800 to a thousand miles away via a propagation mode known as thermal ducting.  This is where a layer of cold air gets sandwiched between two layers of warm air.  This is somewhat rare, and usually doesn't last very long.  Sporadic E can also sometimes cause FM stations to be heard at great distances also.

We, as amateurs, love this kind of stuff, but professional broadcast engineers view these events as nuisance propagation, and they adjust antenna patterns to avoid it, to the extent possible.
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WB8VLC

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Re: how far does fm travel ?
« Reply #3 on: May 26, 2021, 10:00:03 AM »

10 meter FM can travel 10 of thousands of miles with low to mid power and simple antennas.

This past Sunday myself and another ham here in Northwest Oregon were monitoring the North Korean squid fishing boats off of the Russian coast northwest of Japan on 28.175 and 28.275 MHz FM for over 2 hours.

This is a common thing to hear this time of year as there are also many legit ham stations from Japan and other northern pacific regions that appear on 10 meter FM here in the Pacific Northwest on 10 meter FM.

Typically the hams are operating above 29 MHz while the non hams operate anywhere between 27.5 to 39.5 MHz FM using the standard Chicom Fisheries 25 watt FM transceivers.

The radios used on these NK fishing fleets are very simple, 25 watts and typically 102 inch whips and nothing else but with salt water reflection the distances covered are tremendous.
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W2JUV

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Re: how far does fm travel ?
« Reply #4 on: May 26, 2021, 10:39:22 AM »

VHF propagation at broadcast FM frequencies (88-108 Mhz) is primarily line of sight but there is some bending of the signal with curvature of the earth that extends listenable range somewhat. The station in Charlotte on 103.7 is a full Class C facility with 100 kilowatts of effective radiated power, antenna height is 1350 ft above average terrain. Icard NC is about 52mi. from the station's Tx site and well within range of WSOC-103.7 Mhz. Ducting likely has little to do with your reception report.
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VA07

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Re: how far does fm travel ?
« Reply #5 on: May 26, 2021, 11:36:32 AM »

thanks you guys didnt realize it could travel so far
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