I'm the transmitter engineer at one such station, a UHF-TV station with 1000 kw ERP. We accomplish this with 40 kw transmitter output feeding a main antenna with a power gain of 30/1. About 15% of the transmitter power is dissipated through losses in the transmission line running up the tower, so about 33 kw actually reaches the antenna. The antenna power gain is achieved by focusing the radiation into a tight beam aimed at the horizon and slightly below the horizon with very little energy radiated above and below the antenna. It's kind of like a lighthouse you'd see along the coast somewhere. Here's a fun fact: The FCC only counts energy radiated in the horizontal plane against our effective radiated power limit. At my workplace, the main antenna extracts a small amount of energy from the horizontal elements and reradiates it in the vertical plane. This is done to provide a good signal for TV viewers using future mobile phones and for TV's using indoor stick-type antennas. So the final effective radiated power is 1000 kw in the horizontal plane and 300 kw in the vertical plane. Another fun fact: To generate our 40 kw transmitter power output, our transmitter has two 30 kw amplifiers, reduced to 21 kw output each, then combined into one output of 40 kw. To generate this 40 kw, the transmitter consumes about 100 kw of energy from the local utility. That sounds pretty inefficient, and it is, but it's hard to generate power at UHF. A few years ago this transmitter replaced a 20 year old unit that consumed about 150 kw for the same 40 kw output. Back in the 70's, I worked at a UHF-TV station in another city. This station had almost 4.5 megawatts of visual transmitter ERP. They had a gigantic 110 kw transmitter feeding an antenna with a power gain of 50. After transmission line losses, about 89 kw reached the antenna for an ERP of 4450 kw. You can do this at UHF because the wavelength is small and it's possible to build an antenna with a lot of elements, providing a lot of gain.
We used a Comark IOT transmitter from 1998 to 2016, when we replaced it with a Gates Air solid state transmitter. The IOT transmitter efficiency of AC power in to RF power out was about 22%. Our solid state transmitter efficiency AC to RF efficiency is about 37%, which saves a lot in electric power bills. Also, it was no fun working on that IOT rig with 34,000 volts feeding the final amplifiers. I'm glad that transmitter is long gone. We ran the solid state rig for three years before converting it to a different UHF channel in the 2019 repack. In the repack, we were able to install a new antenna in a better position on our tower with a better radiation pattern. @@BroadcastBlueprint
Maybe I could put together a web calculator or Excel sheet to help a newer generation with the same thing! edit: Done! It's at broadcastblueprint.com/tools/tpo_erp_calculator.html
WMJQ (Majik 102) 102.5 FM Buffalo was one of the last 110KW licensed stations that I knew of, and I lived in their market. Boy could they swat a signal *FAR.*
Very well explained mate
Have you ever worked on an uhf tv transmitter where the radiated transmitted power was 1,000,000watts?
I'm the transmitter engineer at one such station, a UHF-TV station with 1000 kw ERP. We accomplish this with 40 kw transmitter output feeding a main antenna with a power gain of 30/1. About 15% of the transmitter power is dissipated through losses in the transmission line running up the tower, so about 33 kw actually reaches the antenna.
The antenna power gain is achieved by focusing the radiation into a tight beam aimed at the horizon and slightly below the horizon with very little energy radiated above and below the antenna. It's kind of like a lighthouse you'd see along the coast somewhere.
Here's a fun fact: The FCC only counts energy radiated in the horizontal plane against our effective radiated power limit. At my workplace, the main antenna extracts a small amount of energy from the horizontal elements and reradiates it in the vertical plane. This is done to provide a good signal for TV viewers using future mobile phones and for TV's using indoor stick-type antennas. So the final effective radiated power is 1000 kw in the horizontal plane and 300 kw in the vertical plane.
Another fun fact: To generate our 40 kw transmitter power output, our transmitter has two 30 kw amplifiers, reduced to 21 kw output each, then combined into one output of 40 kw. To generate this 40 kw, the transmitter consumes about 100 kw of
energy from the local utility. That sounds pretty inefficient, and it is, but it's hard to generate power at UHF. A few years ago this transmitter replaced a 20 year old unit that
consumed about 150 kw for the same 40 kw output.
Back in the 70's, I worked at a UHF-TV station in another city. This station had almost 4.5 megawatts of visual transmitter ERP. They had a gigantic 110 kw transmitter feeding an antenna with a power gain of 50. After transmission line losses, about 89 kw reached the antenna for an ERP of 4450 kw.
You can do this at UHF because the wavelength is small and it's possible to build an antenna with a lot of elements, providing a lot of gain.
Are y'all still on an IOT rig or have you gone solid state with the repack?
We used a Comark IOT transmitter from 1998 to 2016, when we replaced it with a Gates Air solid state transmitter.
The IOT transmitter efficiency of AC power in to RF power out was about 22%. Our solid state transmitter efficiency AC to RF efficiency is about 37%, which saves a lot in electric power bills. Also, it was no fun working on that IOT rig with 34,000 volts feeding the final amplifiers. I'm glad that transmitter is long gone.
We ran the solid state rig for three years before converting it to a different UHF channel in the 2019 repack. In the repack, we were able to install a new antenna in a better position on our tower with a better radiation pattern.
@@BroadcastBlueprint
That brings back fond memories of programming my HP-41C to automate the process somewhat.
Maybe I could put together a web calculator or Excel sheet to help a newer generation with the same thing!
edit: Done! It's at broadcastblueprint.com/tools/tpo_erp_calculator.html
WMJQ (Majik 102) 102.5 FM Buffalo was one of the last 110KW licensed stations that I knew of, and I lived in their market.
Boy could they swat a signal *FAR.*
The station on 101.3 in SF Bay area is still listed as 125kw but strictly directional to nnw and sse to protect 101.1 in Auburn CA.
Y’all seen WBCT Grand Rapids? 320kW ERP at 238m HAAT 🤯
@@BroadcastBlueprint I assume they are using a cp antenna. With that amount of grunt they can afford to.
When KIOI (then KPEN) got the upgrade in the early 60s, 5kW was aimed at the ocean, while the remaining 120 kW was aimed inland.
WBCT runs a 12 bay antenna with full wave spacing. It’s like 8dBd gain