ELLSSUU

I tried sending you a radio question today but your PMs are full.

Question: Are AM stations regulated by the FCC as to how far they can broadcast when it's daylight vs. nighttime? Here in New Orleans 870 AM goes farther at night than day while 1350 AM significantly diminishes at dusk. One of the personalities said it was due to the FCC but didn't elaborate.

Just curious and I new you would know the answer.

Perry 951

All radio stations are power and emission limited due to surrounding stations and topography. Signals can be shaped to protect certain areas or to protect adjacent signals on the same frequency.

AM radio waves are affected by radiation from the sun during the day, so the signal becomes a ground wave transmission. The radio waves remain close to the ground and held there because of the sun and function of the towers and ground straps for the transmitter. When the waves hit something big, like an overpass or building, the radiation is absorbed and the signal cannot continue. At night AM stations broadcast to the atmosphere. Because there is little radiation, AM signals bounce off the stratosphere and earth until the signal is absorbed. Depending on the frequency, power, and tower height, AM signals can go for thousands of miles skipping from earth to atmosphere. This is why most stations cut power or change broadcast pattern at night. AM frequencies are also effected by storms. We've all heard the static on AM when there is lightning, but the storms also trap the signal. You may hear some distant stations, or even some low powered local outlets one night, and then they are gone the next, then back again. Most likely there was a storm between you and the location of the transmitter. Since I don't know specifics about 870 and 1350, I can tell you the examples I know.

WLW in Cincinnati is a full time 50,000 watt station with no pattern or wattage changes. This is a "Clear Channel" frequency. (yea the company too) Since it was the first to broadcast at 5000, 25,000, and 50,000 watts, we had an open license to not limit our power or pattern going back to the 1910s'. Back then, heritage flame throwers like WLW got FCC "Clear Channel" broadcast licenses because they were the only ones on that frequency. Over the years some remained "Clear Channel" and some were limited by power and pattern to protect other stations. Very few AM stations are allowed to broadcast at full nighttime power and open pattern, and even fewer at the 50,000 watt FCC limit. These stations began the broadcast coverage maps for the FCC. Each new signal was designed to limit the intrusion to these massive stations, and is still true today.

1530 WSAI in Cincinnati is also a 50,000 watt full time station, but this one has a night pattern change to protect adjacent stations on the 1530 frequency to the north. You can only get 60 or so miles north of Cinci before the signal dies.. but you can get it pretty directly south of Cinci all the way to Florida.

My first station to program, 970 WATH in Athens OH was 1000 watts daytime, 26 watts at night. We covered about the same area night and day. One evening we had a mode change failure and stayed at 1000 watts. In the morning, I had a message from a very pissed GM of 970 WGTK Evansville IN. Because he powered down to his 40 watt limit, my 1000 watts took up 50-60% of his coverage area. He was listening to my station at his home, rather than his own. (LOL... I still feel bad because I hated it when other stations would overlap my coverage areas)

Stations have to be careful keeping their power and pattern in check. Fines in the MILLIONS are not uncommon if someone screws up big.

FM stations are not effected the same way, so they blast their full allotted power day and night. Radio waves are some strange stuff that I still don't understand too well.

Hope that helps. If you want to know more about the specific signals of 870 and 1350, I can look it up.

ELLSSUU

Wow, awesome answer. Thanks for the info.

Chris_924s

It's calculated and predestined antenna shift based on terrain, client base and transmission power- we do in Wi-Fi for WISP work as well. Same kinda thing- except its full duplex-
Wi-Fi is kinda like an AM/FM radio you talk to.

Are we talking about "Pirate Radio"??

WLS-AM in Chicago is 50K Watts over an omni-directional daily, and 120 degree spread at night- this is why I can get it here at night with a AM Frequency tuned antenna. (Home made dipole)

FWIW "Wolfman Jack" used to be on a 100K watter in Mexico doing a 120 degree (point to point rules for FCC EIRP) in the 60's, 70's and early 80's- THATS why we could pick it up in Chicago at night!

(RF in AM freq travels well over water- actually bouncing between clouds and water-FM is better at this , whereas at 2.4Ghz does not-over water, especially salt water is worse due to particulate matter in the saltwater absorbing the wavelength)

Oh Yeah- I almost forgot- Radio is run by ********. (That's for you Perry!!- BTDT)

Perry 951

Kiss my *** you.... you... you Friend Flipper! I move away and I'm out of the family.... the thanks I get around here. Sheesh.... and I know I was one of the best non ******* radio producers and programmers in the industry. But most of radio is run by ********, you're right about that.

Good call on Wolfman Jack! I did some studies on him back in College when I filed for FCC Operations Compliance. That was a serious blowtorch with an ERP of 180k, dead up the middle of the states. A guy named Art Bell did something like that.

I'll have to take a few of you tech goobers to the transmitter plant in mason, home of the worlds most powerful transmitter (Worlds Largest Wattage... WLW).. 500k monster that needed it's own power plant and cooling towers. The state made it a historical preserve, so it's gonna be renovated and perhaps WLW's main studios will go back. The 500k TX won't ever live again, but it's pretty to look at. The tubes are 6" tall... I'm 6'4 and stood next to one in our GM's office. Impressive.

Here's a little about the site. http://hawkins.pair.com/wlw.shtml
This guy Jim.. he did a wonderful job of documenting the history of WLW. It's an interesting read.

Chris_924s

They put the "Wattage in the cottage" next to the GM's office- Pretty smart- perhaps they were concerned about them reproducing..

I am, of course, just kidding. all the time I was in Radio I did meet one nice guy.

Bri Bro

Perry, we just pulled 16 of these eight foot klystron tubes out of Denali Alaska. Each is rated at well over 1,000,000 watts and by running four at a time, they had a 5,000,000 watt transmitter. New, each one of these tube cost $250,000 but the goverment was giving them away.

Perry 951

Get me one!!!!

What is the transmitter transmitting.... 5,000,000 watts, it should be something pretty damn good!

Bri Bro

They came out of the Ballistic Missile Early Warning System (BMEWS). We are going to use two at a time to make a 1,000,000 Watt RF amplifier.

Perry 951

Sweet.

951Porschiste

This is so OT but I'd like to share:
Back in 1976, I had a summer job in a mining company called QCM (Quebec Cartier Mining) up in northern Quebec. This place was close to Labrador. The company had its own railway to transport iron ore from its mines down to the Gulf of St-Lawrence. Every now and then the rail line would need emergency repairs and they had to fabricate their own rock ballast out of huge chunks of rocks from a quarry. I was responsible for measuring the amount of ballast produced per work quarter. Sometimes we had to go to the quarry in the middle of the night because of an emergency on the line. I had a small transistor radio and I could sometimes pick up the (then) hippest AM radio station in Montreal: CKGM 980. I could never pick it up during the day. Thing is we were some 900 miles away from Montreal!
Thanks for the explanation Perry951.