• Get involved.
    We want your input!
    Apply for Membership and join the conversations about everything related to broadcasting.

    After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
    If you use a disposable or false email address, your registration will be rejected.

    After your membership is approved, please take a minute to tell us a little bit about yourself.
    https://www.radiodiscussions.com/forums/introduce-yourself.1088/

    Thanks in advance and have fun!
    RadioDiscussions Administrators

70s AM powerdown

C

Cheesewater

I am curious about how many different ways there were to power down AM stations at night in the US in the 1970s.
Was it always as simple as pushing a button or were there more technical or complicated ways of reducing power, dependent on the age of the equipment?

Thank you for your input (and output)!
 
Cheesewater said:
I am curious about how many different ways there were to power down AM stations at night in the US in the 1970s.
Was it always as simple as pushing a button or were there more technical or complicated ways of reducing power, dependent on the age of the equipment?

Thank you for your input (and output)!
Click to expand...

This is a very simplified explanation of a rather more complicated subject that changed over time as technology developed.

There are really two ways of powering down. The first is by selecting the proper power on one transmitter and having it reduce power. The second is by having a different transmitter for each mode of operation.

Older transmitters, particularly tube models, had to be ordered with the proper cutback levels.

Because there were were 6 Class IV channels where for some time 1 kw days and 250 watts at night was the standard, manufacturers had a model for cutback to 250 watts. With solid state transmitters, the ability to have programmed power presets at almost any level became possible. And many regional channel stations ran with 5 kw day and 1 kw nights, and manufacturers could offer single units that ran well at each level.

Problems came when the FCC let stations have nearly any power level.

Prior to that, the FCC had only a few power levels, 100, 250, 500 watts and 1 kw, 5 kw, 10 kw, 25 kw and 50 kw. You could not have, for example, 780 watts or 13,450 watts.

When the FCC changed to allow stations that could increase power to pick the exact and highest possible level, manufacturers had to enable the ability to run at preset but almost random power levels. The advent of solid state transmitters with computerized controls made this relatively easy.

With stations with huge day and night power differences, it was generally more economical to have a low power night transmitter, as running the big transmitter at very low power was not efficient. This would be the case when Robin Mathis build a number of 50 kw day, 250 watt night stations in Mississippi.

A seldom used old practice was to use a resistive network to burn off some power when standard power options from makers of transmitters were not available.
 
Last edited:
Really old equipment could be a serious pain to power down. Partly because power-down also came with a directional pattern change. So the antenna impedance would change -- maybe substantially -- which could cause the transmitter to fold back. However, in such cases it would generally be advisable to fix the antenna tuning unit to properly match the night array. That was certainly possible in the 70s, but the theory was not well understood until (I want to say...) the 40s.
 
PTBoardOp94 said:
Really old equipment could be a serious pain to power down. Partly because power-down also came with a directional pattern change. So the antenna impedance would change -- maybe substantially -- which could cause the transmitter to fold back. However, in such cases it would generally be advisable to fix the antenna tuning unit to properly match the night array. That was certainly possible in the 70s, but the theory was not well understood until (I want to say...) the 40s.
Click to expand...

Antenna impedance, including resistance and reactance, were well understood in the 30's. The problem was more in the construction and design of components and the difficulty in doing measurements of the system.

For directional systems, there is a common point where the transmitter feeds the antenna system, whether one tower or twelve. That point is tuned to match the output of the transmitter. Now, as back in the 30's, the common point for day and night operations were designed to present essentially the same impedance to the transmitter.

Today systems are designed by computer. Back in the 40's, Carl Smith developed a "mechanical computer" to design thousands of directional patterns and the spacing and tuning elements of each. Transmitters don't like working into a mis-matched load and some are very intolerant of them.
 
DavidEduardo said:


This is a very simplified explanation of a rather more complicated subject that changed over time as technology developed.

There are really two ways of powering down. The first is by selecting the proper power on one transmitter and having it reduce power. The second is by having a different transmitter for each mode of operation.

Older transmitters, particularly tube models, had to be ordered with the proper cutback levels.

Because there were were 6 Class IV channels where for some time 1 kw days and 250 watts at night was the standard, manufacturers had a model for cutback to 250 watts. With solid state transmitters, the ability to have programmed power presets at almost any level became possible. And many regional channel stations ran with 5 kw day and 1 kw nights, and manufacturers could offer single units that ran well at each level.

Problems came when the FCC let stations have nearly any power level.

Prior to that, the FCC had only a few power levels, 100, 250, 500 watts and 1 kw, 5 kw, 10 kw, 25 kw and 50 kw. You could not have, for example, 780 watts or 13,450 watts.

When the FCC changed to allow stations that could increase power to pick the exact and highest possible level, manufacturers had to enable the ability to run at preset but almost random power levels. The advent of solid state transmitters with computerized controls made this relatively easy.

With stations with huge day and night power differences, it was generally more economical to have a low power night transmitter, as running the big transmitter at very low power was not efficient. This would be the case when Robin Mathis build a number of 50 kw day, 250 watt night stations in Mississippi.

A seldom used old practice was to use a resistive network to burn off some power when standard power options from makers of transmitters were not available.
Click to expand...

Wow... I knew the late Robin Mathis personally. Haven't heard his name mentioned in a while. The 50 kW day / 250 W night stations that he and his brother Marvin put together were something to see. Both 50 kW stations are still in operation in Mississippi, but have been updated with solid state transmitters over the years by new owners.
 
rfburns said:
Wow... I knew the late Robin Mathis personally. Haven't heard his name mentioned in a while. The 50 kW day / 250 W night stations that he and his brother Marvin put together were something to see. Both 50 kW stations are still in operation in Mississippi, but have been updated with solid state transmitters over the years by new owners.
Click to expand...


My mothers first cousin J.B. Skelton worked with the Mathis brothers at WCPC in Houston, MS. If I'm not mistaken one of them (Marvin?) died in an accident years ago. I believe his wife ran WSJC in Magee. J.B. Skelton died of cancer several years ago. We used to visit them at his moms house in Mantee, MS when I was a kid.
 
Pat3 said:
My mothers first cousin J.B. Skelton worked with the Mathis brothers at WCPC in Houston, MS. If I'm not mistaken one of them (Marvin?) died in an accident years ago. I believe his wife ran WSJC in Magee. J.B. Skelton died of cancer several years ago. We used to visit them at his moms house in Mantee, MS when I was a kid.
Click to expand...

That is correct - Marvin was killed in an accident several years ago. His wife took over and eventually his son Mike ran the station for several years. Never met J.B. personally but saw a lot of his work while doing contract engineering for both WSJC and WCPC.
 
rfburns said:
That is correct - Marvin was killed in an accident several years ago. His wife took over and eventually his son Mike ran the station for several years. Never met J.B. personally but saw a lot of his work while doing contract engineering for both WSJC and WCPC.
Click to expand...

I worked for a couple of years (1974-1976) while in high school for the Mathis family at the ex-WSAO in Senatobia. Marvin was killed in a car train accident in 1961 or 1962, just prior to WSAO going on the air in 1962. Marvin's wife, Jennette, ran the 50 kW, WSJC, in McGee for many years. They had another person, Fannie Mae Cothran who ran their WXTN in Lexington, MS for many years. I knew J.B. Skelton and assisted him with several audio proofs on WSAO. Both WCPC in Houston, MS and WSJC had FM stations (I can recall J.B. doing an air shift on the Houston FM when I visited one day). The other Mathis brother involved in the business was Ralph Mathis.

Both 50 kW stations and WSAO (5 kW) had ITA transmitters when they went on the air and for many years. The 50 kW ITA transmitters at WCPC and WSJC were two of only a very few constructed. The WSJC ITA transmitter almost killed a business partner of mine in the early 1990s when he was working on it. The modulation choke had shorted to ground so someone had put it up on wooden blocks.

The Mathis family could have easily had an FM license in Senatobia in the early 70's as there was a channel assigned. Another group moved that channel to Coldwater and put WVIM on the air in 1976. Now, Senatobia, doesn't have a local station, AM or FM, after Northwest Community College discontinued their broadcast program and sold WNJC. Latter, the owner of WSAO, Jesse Ross, got fined by the FCC for EAS violations and couldn't or wouldn't pay the $21k fine.


More on topic, I was part of the crew that relocated the transmitter site of what was WBAM and became WLWI-AM, 50 kW Day, 740 kHz. in Montgomery, AL in 1985. The FCC had just granted daytime AM stations nighttime power, subject to interference calculations, at some level. WLWI's night power was assigned as 233 watts. Rather than try to run a lower power on the MW-50 transmitter, they purchased a 1 kW Continental 314R1 "Power Pebble" for night operation.


Bob
 
Dr. Bob said:
I worked for a couple of years (1974-1976) while in high school for the Mathis family at the ex-WSAO in Senatobia.
Click to expand...

Bob,

Fascinating post. I remember hearing tests of Houston and McGee when they were being built, and was always curious about the 250 watt night power. You answered a lot of my questions.
 
Dr. Bob said:
I worked for a couple of years (1974-1976) while in high school for the Mathis family at the ex-WSAO in Senatobia. Marvin was killed in a car train accident in 1961 or 1962, just prior to WSAO going on the air in 1962. Marvin's wife, Jennette, ran the 50 kW, WSJC, in McGee for many years. They had another person, Fannie Mae Cothran who ran their WXTN in Lexington, MS for many years. I knew J.B. Skelton and assisted him with several audio proofs on WSAO. Both WCPC in Houston, MS and WSJC had FM stations (I can recall J.B. doing an air shift on the Houston FM when I visited one day). The other Mathis brother involved in the business was Ralph Mathis.

Both 50 kW stations and WSAO (5 kW) had ITA transmitters when they went on the air and for many years. The 50 kW ITA transmitters at WCPC and WSJC were two of only a very few constructed. The WSJC ITA transmitter almost killed a business partner of mine in the early 1990s when he was working on it. The modulation choke had shorted to ground so someone had put it up on wooden blocks.

The Mathis family could have easily had an FM license in Senatobia in the early 70's as there was a channel assigned. Another group moved that channel to Coldwater and put WVIM on the air in 1976. Now, Senatobia, doesn't have a local station, AM or FM, after Northwest Community College discontinued their broadcast program and sold WNJC. Latter, the owner of WSAO, Jesse Ross, got fined by the FCC for EAS violations and couldn't or wouldn't pay the $21k fine.


More on topic, I was part of the crew that relocated the transmitter site of what was WBAM and became WLWI-AM, 50 kW Day, 740 kHz. in Montgomery, AL in 1985. The FCC had just granted daytime AM stations nighttime power, subject to interference calculations, at some level. WLWI's night power was assigned as 233 watts. Rather than try to run a lower power on the MW-50 transmitter, they purchased a 1 kW Continental 314R1 "Power Pebble" for night operation.


Bob
Click to expand...

Wow... bringing up a lot of history! I did meet Marvin's brother, Robin Mathis at WCPC a few years ago. He was in his late 80's and still coming in to work at the station until his passing last year. I had forgotten about the Mathis family connection to WXTN - Fannie Mae Cothren's son Brad was running WXTN when I first went to Lexington, Ms to do some engineering. Brad passed away shortly thereafter and his wife took over operation of the station for a while.
 
70s AM Powerdown

rfburns said:
Wow... bringing up a lot of history! I did meet Marvin's brother, Robin Mathis at WCPC a few years ago. He was in his late 80's and still coming in to work at the station until his passing last year. I had forgotten about the Mathis family connection to WXTN - Fannie Mae Cothren's son Brad was running WXTN when I first went to Lexington, Ms to do some engineering. Brad passed away shortly thereafter and his wife took over operation of the station for a while.
Click to expand...

WCPC required two additional towers for the night operations since 940 kHz. is a Mexican clear channel and they had to produce some tight nulls. It made for a big "tower farm" in little Houston, MS. I just wish I knew what I know now about AM DAs so I could ask J.B. Skelton questions about the construction of those DAs. Looking at the FCC history card file for WCPC, they first were on 1320 kHz. with 1 kW in 1955, then they moved to 940 in 1960 with 10 kW and applied for 50 kW in '63 with the license granted in 1964. They didn't apply for night until 1968 and then at 500 watts. They corrected that to 250 watts in 1971. They requested extensions of the completion date many times and finally got a license for the night operation in 1981!

There was talk about people who knew the history of WSAO that the Mathis family was going to try to increase the day power to 50 kW but, with Marvin's untimely death, that effort fell by the wayside. In the late 70's, WSAO changed from 1550 kHz. to 1140 kHz. still day only. I was at Mississippi State at the time but did discuss what was required with J.B. They added a pole to the tower for extra length and, of course, had to retune the transmitter and ATU. Unfortunately, when the FCC was handing out night power in the mid-80's, WSAO got no night power, since it is on a U.S. clear channel (WRVA). Ironically, they might have gotten some night power on 1550 kHz. as it is a Mexican clear channel. When I was there, they did have pre-sunrise authority with 500 watts (on 1550 kHz.) from 6 AM to local sunrise. I worked Saturday sign-on for a couple of years and forgot to change to 5 kW a time or two.

Dr. Bob
 
What has become of WXTN in Lexington. I checked the internet and it was streaming and simulcasting with WONG in Canton, MS. It used to have 5000 watts and get into Jackson a little bit on a clear day but I haven't heard it in a long time. WONG and it's FM simulcast is also off the air as well. I heard it on the air a couple of weeks ago for maybe one day and then it went silent
 
Pat3 said:
What has become of WXTN in Lexington. I checked the internet and it was streaming and simulcasting with WONG in Canton, MS. It used to have 5000 watts and get into Jackson a little bit on a clear day but I haven't heard it in a long time. WONG and it's FM simulcast is also off the air as well. I heard it on the air a couple of weeks ago for maybe one day and then it went silent
Click to expand...

WXTN's old 5kw AM transmitter failed years ago. They "rented" a 1kw transmitter for a while, but I understand they lost it after falling behind on rental payments. I haven't heard it on in over a year now. WONG has been a dumpster fire for quite a while now - they got popped by the FCC for running the translator while the AM was off the air.
 
"With stations with huge day and night power differences, it was generally more economical to have a low power night transmitter, as running the big transmitter at very low power was not efficient. This would be the case when Robin Mathis build a number of 50 kw day, 250 watt night stations in Mississippi.

A seldom used old practice was to use a resistive network to burn off some power when standard power options from makers of transmitters were not available."

1580 AM in Georgetown, Kentucky had a unique way of achieving 48 watts nights from 10kw days. A 1kw rig fed a dummy load while the mod monitor output, just happen to produced the voltage to make it work, fed the array. Plant was rebuilt buy current owner twenty years ago to a different configuration. :)
 
Status
This thread has been closed due to inactivity. You can create a new thread to discuss this topic.
Back
Top Bottom