Long distance FM

[averagelistener]

I do not pretend to understand the science of radio waves much less the difference between FM and AM. So I am going to ask this question because I don't know and I would like to understand something.

This morning as I was driving I was able to pick up WOBB 100.3 from Albany, GA about 15 miles north of Gainesville, GA. What would make that happen?

 

[fussbudget]

Tropospheric ducting. In this case, cold air trapped close to the earth's surface, with a layer of warm air in the upper reaches of the atmosphere, causes the FM signals to travel much further than they normally would. There are several different ways to receive FM stations over a long distance. One of my favorites occurs most often in the summer months, when "Sporadic E," causes FM and TV signals to travel hundreds, even thousands of miles.Sporadic E is an unpredictable natural phenomenon the occurs in the E region of the ionosphere. Sitting in your car in Gainesville, it is possible to hear stations in Mexico, Texas, Colorado, Canada and many other places, for a few minutes to a few hours, depending on the strentgh of the opening.

 

[OnTheAir123]

The 2m ham band, 144-148 Mhz, was also open last night from 9pm until after 2am. One Atlanta area repeater had stations using it from Louisiana. We had a duct going from South Carolina to Mississippi. Lot's O Fun.

 

[ssnake]

This affected WREK this morning: staff in our studio were complaining about "distortions" in the air signal. This despite that (1) our studio is only 1 km from the antenna, (2) we have an FM yagi pointed straight at the antenna with clear line-of-sight, and (3) our receive equipment is an expensive Belar mod monitor. Who knows where our power was actually going....

 

[hipporadio]

My most outstanding experience with this was in early-June 1974 on a Saturday morning when the FM band in eastern Indiana became “home” to nearly every Miami station that was not on a locally-populated frequency. I remember 3-hours of Classical WTMI overpowering my favorite WNAP in Indianapolis on 93.1. As the morning progressed, the skip seemed to head north (Vero Beach, Daytona, Orlando—eventually Savannah and Macon). This condition started at daybreak and lasted until about 2PM.

I remember a spring morning in 1976 when WQLK—Richmond, IN received dozens of calls from listeners asking if they were off-the-air—seems WHNN Bay City/Saginaw, MI was overpowering their 50kw signal IN TOWN! The same happened in South Bend, IN in July 1979 when WBIZ 100.7 Eau Claire, WI made an appearance in mid-afternoon—covering then Beautiful Music WYEZ in nearby Elkhart on 100.7 which was rumored to be planning a flip to CHR. WBIZ (as Z-100) faked out the management of local WNDU-FM (planning a similar flip) who had heard the rumors and caught the WBIZ “trop” at their Notre Dame campus studios—thinking a change on local WYEZ had occurred.

I remember my CE telling me once; "When we're getting clobbered, we're coming in WAAAAY down the road".

 

[nightmanager]

Most interesting ducting I personally ever experienced was a signal from TV station KGBT-4 in Harlingen, Texas, which I picked up on a really crappy 12" b/w TV here in Atlanta.

No special equipment either: this was a "Kmart special" $50 TV which was probably second hand. And I think the aerial was broken too.

At the time, I was trying to look at the old low power VHF channel 4 we used to have in town. IIRC, they used to run music videos much like channel 69 did in the early WVEU days before they changed to the WVUE call. Anyway, the signal from 1100 miles away in Texas was actually much clearer than the local low power. Go figure.

What's this got to do with FM ducting? Nothing except TV 4 is only 16Mhz below the start of the FM band. If TV-4 can duct a thousand miles, expect similar things from FM stations.

 

[KStar8706]

I'm not an expert by any means when it comes to how weather conditions effect radio signals, but it seems to me that altitude must play a great deal as to what signals can be received. Perhaps the it's the colder air at higher altitudes since electricity always travels better at lower temps, or (and this I kind of doubt) you are just simply closer to the reflecting ionosphere so there is not as much interference from the troposphere. I'm live on a hill here in the northside of Atlanta and notice I can pick up Chattanooga's KZ-106 better than I can if I leave home and move to lower ground. If anyone knows better than me, fill free to clear me up.

By the way, isn't TV 4 still on the air showing Spanish language programming? I used to be able to pick it up back when it was showing ShopNBC.

 

[IT_Guru]

Yep it's still there ... in fact if you have DirecTV and subscribe to the local channels you can get it there too.

By the way, isn't TV 4 still on the air showing Spanish language programming? I used to be able to pick it up back when it was showing ShopNBC.