Different frequencies for day and night.

[Icangelp]

On AM, I can only think of one station.

WNZK in Dearborn, MI
DA-2
Day 690 KHZ 2.5 KW
Night 680 KHZ 2.5 KW

CHYR/CHIR in Leamington, ON CAN used to operate on 710 KHZ days as CHYR (Cheer), then switched to 730 KHZ at night under the CHIR call letters, although I don't remember ever hearing "CHIR". CHYR wasn't a nightly signal in Indy and Cincinnati, but they were regularly heard.

[cd637299]

I believe that until fairly recently, WLES serving Richmond VA was on 580 days & 590 nights, but they are 590 all the time now.

I'm sure there have been others, but I just cannot think of any right now.

cd

[borderblaster]

I remember CHIR, and also the 730 frequency being called CHYR-7. CHYR is on FM now.

[Steve Green NEPA]

Was quite some time back,   but WBAP and WFAA out of the Dallas TX area used to swap/alternate days and nights between 570 and 820.    Perhaps someone here will remember that wardrobe change ;   how it came about ;  where it eventually went.

Also,  iIrc (which I doubt) ,  the 730 Canadian station in Leamington and WAEB Allentown 790 were the only two stations that raised their  power at night .....       

[Icangelp]

Was quite some time back,   but WBAP and WFAA out of the Dallas TX area used to swap/alternate days and nights between 570 and 820.    Perhaps someone here will remember that wardrobe change ;   how it came about ;  where it eventually went.

Also,  iIrc (which I doubt) ,  the 730 Canadian station in Leamington and WAEB Allentown 790 were the only two stations that raised their  power at night .....       

Steve.
I can remember 570/820 WBAP/WFAA alternating frequencies, but I don't recall the schedule. I was living in Kansas City when they settled on one frequency, so it must have been in 1969 or '70 when that happened.

I'd be interested to hear how it was decided which station settled on which frequency.

Edit: Info on the old 570/820 split is available in serveral places.
820 Kilocycles
WBAP Midnight-7:30am
WFAA 7:30am-12:30pm
WBAP 12:30pm-5:00pm
WFAA 5:00pm-Midnight

[Scott Fybush]

I believe that until fairly recently, WLES serving Richmond VA was on 580 days & 590 nights, but they are 590 all the time now.

I'm sure there have been others, but I just cannot think of any right now.

cd

I don't believe WLES ever actually operated as a split-frequency station. It was a fulltimer on 580 and became a fulltimer on 590 through a frequency swap with WLVA in Lynchburg. Because of some quirks in the way the FCC database system works (and some even bigger quirks in the way sites like radio-locator display information from the database), it appeared briefly as a split-frequency, but I believe that was only on paper.

[borderblaster]

How did that WBAP/WFAA thing make the slightest bit of sense?

[jd]

In addition to the 710-730 arrangement in Leamington, there were a couple of other split-frequency operations in Canada.

In the mid 1960's CHFI Toronto, a daytimer on 1540, was allowed to operate at night on 680.  This was short-lived, however, since they were soon authorized to operate on 680 full-time and 1540 would become the home of CHIN.  CHFI was the forerunner of today's CFTR.

In Gravelbourg, Saskatchewan there was a split-frequency arrangement beginning in the mid-1950's, with CFRG 1230 being allowed to use 710 for daytime operation with 5,000 watts.  The CFRG call letters went to 710, while the 250-watt nighttime station on 1230 was known as CFGR.  After a couple of decades a plan to end the dual-frequency operation was approved, resulting in the eventual appearance of CBKF, full-time on 690.   

[Scott Fybush]

How did that WBAP/WFAA thing make the slightest bit of sense?

In its day, it made plenty of sense, at least politically. 820 (and before 1941, 800) was one of only two I-A clear channels allocated to Texas, and the intense rivalry between Dallas and Fort Worth (which were separate radio markets until 1971) would have resulted in one city or the other being slighted by a full-time allocation of the big signal to the other one. Amon Carter, the powerful publisher of the Fort Worth Star-Telegram, wasn't going to be slighted in that way, and I'm sure he put a lot of pressure on the FCC to split 800/820 between the cities.

It wasn't all that terribly confusing for listeners, either: NBC was always on 820, ABC was always on 570, and in the days when the networks ruled the radio airwaves it was only the local content that moved back and forth.

By the 1960s, it made much less sense, and the Star-Telegram finally bought out the Dallas Morning News in 1970 to end the share-time.

[jd]

By the 1960s, it made much less sense, and the Star-Telegram finally bought out the Dallas Morning News in 1970 to end the share-time.

And as a result, 820 got even "more cowbell."