Running reduced power on 1230kHz.

[radiotower40]

I know of a talk station authorized with the standard 1kW power level, day and night, as most station's on 1230 kHz are.

They need to do work to improve their site. I do not know all the specifics on the work.

The contact I have at the station told me that they are going to ask for STA to operate at 100 watts for a short time to do some work.

They would also have to shut down entirely some nights, for a couple hours to do the needed work.

They are not building a new tower, they will use the licsensed site for STA.

Will the FCC grant such an STA? What interests me most about this is how far will the station be heard at that power level, on a congested graveyard?

My thinking is they may be Ok during the day, however is this even worth running during CH and night?

I know a lot of stations run lower power on other channels and it serves them.

Most of the population they target are within ten miles of the site, so they are able to serve the core fine with 1kW.

I know all places have different variables, if you had to guess though, based on the frequency and the issues with a graveyard channel, especialy at night, could you give an educated guess as to how far this station would be listenable by day, and by night?

Would we be looking at 2, 3, 5 miles of useful service, or are we talking about having to be in the parking lot next to the tower to recieve it?

Anyone that can add their expertise here, please do so.

This is more out of curiosty than need to know for me. I find engineering issues extremely interesting, unfortunately I lack the knowledge that you have.

I know that a station that never upraded facilities are, on paper at least to operate at 100 watts, I know of none that exsist though.

 

[rfry]

Below are the distances to various field intensities based on the conditions shown, using the FCC groundwave propagation chart for that frequency and power, and an assumed earth conductivity of 5 mS/m (about average).

These distances assume that the station is using a 1/4-wave vertical monopole with an r-f ground system of 120 x 1/4-wave buried radials, all in good condition.

A 2 mV/m field could provide reasonably good service to indoor radios in a private home, depending on local noise and interference.

Nighttime interference from co-channel stations could reduce the effective coverage provided by all of these fields.

Frequency = 1230 kHz
Power = 0.10 kW
Inverse Distance Field at 1 mile = 60.1 mV/m
Conductivity = 5.0 mS/m

Field Intensity Distance to contour
20 mV/m 2.07 miles
10 mV/m 3.46 miles
5 mV/m 5.48 miles
2 mV/m 9.22 miles

 

[BobOnTheJob]

I know of a talk station authorized with the standard 1kW power level, day and night, as most station's on 1230 kHz are.

They need to do work to improve their site. I do not know all the specifics on the work.

The contact I have at the station told me that they are going to ask for STA to operate at 100 watts for a short time to do some work.

They would also have to shut down entirely some nights, for a couple hours to do the needed work.

They are not building a new tower, they will use the licsensed site for STA.

Will the FCC grant such an STA? What interests me most about this is how far will the station be heard at that power level, on a congested graveyard?

My thinking is they may be Ok during the day, however is this even worth running during CH and night?

I know a lot of stations run lower power on other channels and it serves them.

Most of the population they target are within ten miles of the site, so they are able to serve the core fine with 1kW.

I know all places have different variables, if you had to guess though, based on the frequency and the issues with a graveyard channel, especialy at night, could you give an educated guess as to how far this station would be listenable by day, and by night?

Would we be looking at 2, 3, 5 miles of useful service, or are we talking about having to be in the parking lot next to the tower to recieve it?

Anyone that can add their expertise here, please do so.

This is more out of curiosty than need to know for me. I find engineering issues extremely interesting, unfortunately I lack the knowledge that you have.

I know that a station that never upraded facilities are, on paper at least to operate at 100 watts, I know of none that exsist though.

I don't believe an STA is needed for reduced power operation that does not exceed 10 days. And a station need only operate 2/3 of it's authorized hours from 6PM-midnight, so they could shut down for several hours every night at 10PM with no further authority. As far as coverage goes, if the tower is smack dab in the middle of a small population center (say 20,000 people), most listeners wouldn't notice a drop from 1000 watts to 100 watts. In radio, the first watt is far more important than the second watt. While it sounds like a 90% drop in coverage would result, that's not the case. The relationship between power and coverage is not a linear one. Each time you drop the power by a factor of 4, the signal strength drops by a factor of 2. In the example that R.Fry posted, the 1000 watt signal at 9.22 miles would be 20mv if it were a linear relationship. He can illustrate the difference between 100 watts and 1000 watts more eloquently than can I if he'll be so kind. This relationship of power vs signal is a good starting point in understanding the basics of radio station coverage.

 

[rfry]

The relationship between power and coverage is not a linear one. Each time you drop the power by a factor of 4, the signal strength drops by a factor of 2. In the example that R.Fry posted, the 1000 watt signal at 9.22 miles would be 20mv if it were a linear relationship.

But instead, the value of the field at 9.22 miles would change as the square root of the power change, resulting in a field of 2 * 3.162 = 6.324 mV/m.

Here are the distances to those same contours for the same assumptions, with 1 kW of applied power:

Field Intensity Distance to contour
20 mV/m 4.70 miles
10 mV/m 7.19 miles
5 mV/m 10.42 miles
2 mV/m 16.13 miles

 

[w9wi]

Don't take this too horribly seriously as I've not been to the site in nearly 20 years but...

if this is the station I'm thinking it is, the tower is centrally located & should cover the town pretty well at 100 watts. Except that I suspect there may be problems with the ground system. (which is probably what they're looking to fix; something that requires power reduction but doesn't involve replacing the tower certainly sounds like ground system work to this TV guy.)

The way I read 73.1560, Bob is correct, STA is not required for reduced power operation for less than 30 days. If it exceeds 10 days, the FCC must be notified. (but no permission is required)

 

[radiotower40]

Thank you for the time you put in to answer my questions! I always learn so much here.

If you feel like going a little more, I would love to hear more about the power levels. I guess I am like most people who just assume that if you double your power, from say 5kW to 10kW, you double your coverage area, when in fact it doesn't work that way.

Thanks again, there is a lot of "smarts" around here and believe me I can use all I can get