What is ERP?

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xusmarine1979

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I'm sure this has been answered before but I couldn't find it in a search and wasn't sure where to place this. But can someone give me a simple explenation of what ERP is and what the difference is between that and the maximum output? anyone that could shine a light on this subject I would be most greatful.

I'm curious because my county is going from a smart/zone TRS to a simulcast, and right now I believe the ERP is 125 and they are bumping it up to 250. Does this mean I'll be able to get a better signal?
 

RKG

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I'm sure this has been answered before but I couldn't find it in a search and wasn't sure where to place this. But can someone give me a simple explenation of what ERP is and what the difference is between that and the maximum output? anyone that could shine a light on this subject I would be most greatful.

I'm curious because my county is going from a smart/zone TRS to a simulcast, and right now I believe the ERP is 125 and they are bumping it up to 250. Does this mean I'll be able to get a better signal?

Effective Radiated Power.

It is the Transmitter Power as augmented by antenna gain and diminished by system losses, such as duplexer insertion loss and feedline loss.

Antenna gain and system losses are expressed in decibels (dB). When you have the net gain/loss in dB (could be either a positive or negative number), apply it as follows:

Divide dB by 10.
Raise the number 10 to that power.
Multiply transmitter output by the result.

Example:

Transmitter Power = 110W
Antenna Gain = 10 dB
System Loss = 3.25 dB

Net System Gain is 6.75 dB.
Divide by 10 is .675
10 to the .675 power is 4.73.
110 times 4.73 is 520.3.
ERP = 520W
 

ka3jjz

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Because it's never been added? Go ahead and do so...others will thank you for it....73 Mike
 

RKG

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Does height come into play here?

I notice looking @ licenses for the State of Maine (mountain-top repeaters) I sometimes see 100 watts,
with a ERP of 350 watts?

Height plays no part in the ERP calculation.

Height, though, does affect the distance to the radio horizon, which has an effect on the potential range of a station. The approximate formula for radio horizon is

H(n. mi.) equals 1.34 times AntHt (feet).

However, height of an antenna has to be coordinated with its electrical gain. Electrical gain, which is measured in the horizontal plane, is accomplished by focussing radiated energy from other vertical radials into the horizontal plane. Mounting an antenna with high gain at high elevation tends to produce the "lighthouse effect," wherein signals pass over the heads of nearby receivers.

All of which reinforces the notion that system design is a complex engineering analysis, not to be accomplished on the basis of simplistic constituent equations by themselves.
 

wa8pyr

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Divide dB by 10.
Raise the number 10 to that power.
Multiply transmitter output by the result.

A simple rule of thumb to follow if you just need a quick rough ERP figure in the field is to remember that for every 3dB of gain the signal strength doubles.

110*2 = 220 (3dB)
220*2 = 440 (6dB)
110*.75 = 82.5 (6.75dB)

440+82.5 = 522.5

Close enough for rough figuring in the field, but if you're doing official paperwork, use the proper formula...
 

lost_in_maine

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Height plays no part in the ERP calculation.

Height, though, does affect the distance to the radio horizon, which has an effect on the potential range of a station. The approximate formula for radio horizon is

H(n. mi.) equals 1.34 times AntHt (feet).

Thanks, great explanation, and learned a lot from this thread
 

greghahn

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I'm sure this has been answered before but I couldn't find it in a search and wasn't sure where to place this. But can someone give me a simple explenation of what ERP is and what the difference is between that and the maximum output? anyone that could shine a light on this subject I would be most greatful.

I'm curious because my county is going from a smart/zone TRS to a simulcast, and right now I believe the ERP is 125 and they are bumping it up to 250. Does this mean I'll be able to get a better signal?


It stands for "Effective Radiated Power". It is the result of antenna input power multiplied by antenna gain.

The antenna input power is found by subtracting transmission line losses from transmitter output power.

So ERP is the true determiner of coverage, because it takes antenna gain and transmission line loss into account.

You will get a better signal, IF their transmitting antenna remains at the same height.
 
N

N_Jay

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. . . So ERP is the true determiner of coverage, because it takes antenna gain and transmission line loss into account. . . . . .


No, it is ONE determiner of coverage, that takes several factors into account.
 

greghahn

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No, it is ONE determiner of coverage, that takes several factors into account.


Taking me out of context makes you look very smart. Kudos on that.

The original question was about the difference between ERP and output power. In that context, by reply is correct. Notice also my reply made reference to antenna height. We can assume that neither the tower location nor interfering factors have changed. I suppose we could get into beam tilt, but again, the original question was about the difference between TPO and ERP.

Thanks for your insight.
 
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N_Jay

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Taking me out of context makes you look very smart. Kudos on that.

The original question was about the difference between ERP and output power. In that context, by reply is correct. Notice also my reply made reference to antenna height. We can assume that neither the tower location nor interfering factors have changed. I suppose we could get into beam tilt, but again, the original question was about the difference between TPO and ERP.

Thanks for your insight.

Sorry, but all your additional words do not make your statement correct.

Thought it might be good to clarify it for those that are just learning.

Actually, going back to the original question, someone should clarify the difference between the actual power output, and/or ERP and the "Maximum Power Output" and/or "ERP" listed on an FCC license.
 

greghahn

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Sorry, but all your additional words do not make your statement correct.

Thought it might be good to clarify it for those that are just learning.

Actually, going back to the original question, someone should clarify the difference between the actual power output, and/or ERP and the "Maximum Power Output" and/or "ERP" listed on an FCC license.


I think we both agree that between TPO and ERP, ERP is the true determiner of coverage. That's all I was saying because that's all he was asking.
 
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N_Jay

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I think we both agree that between TPO and ERP, ERP is the true determiner of coverage. That's all I was saying because that's all he was asking.


While ERP is the proper way to discuss power when you are considering coverage, there are so many factors that are much more important.
It most certainly is NOT the ONE determiner, and it is kind of a stretch to call it the "true determiner".
As for the original question, about what ERP is an how it is different from "Output power", that has been well covered.
On the question; "Does this mean I'll be able to get a better signal?", the answer is not clear.
A licenses change is a paper change, they may or may not design the new system to the maximum on the license, additionally, we don't know if the old system is running it its license maximum.
So in the end we don't know if the power is going up, staying the same, or gong down.

Also, since they are going to simulcast, there is a chance that he may be in an area with good signal level but a high level of simulcast distortion, making the system unintellegible (or at least "worst sounding" than it is currently).

Simple questions sometimes have complex answers.
 

greghahn

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While ERP is the proper way to discuss power when you are considering coverage, there are so many factors that are much more important.
It most certainly is NOT the ONE determiner, and it is kind of a stretch to call it the "true determiner".
As for the original question, about what ERP is an how it is different from "Output power", that has been well covered.
On the question; "Does this mean I'll be able to get a better signal?", the answer is not clear.
A licenses change is a paper change, they may or may not design the new system to the maximum on the license, additionally, we don't know if the old system is running it its license maximum.
So in the end we don't know if the power is going up, staying the same, or gong down.

Also, since they are going to simulcast, there is a chance that he may be in an area with good signal level but a high level of simulcast distortion, making the system unintellegible (or at least "worst sounding" than it is currently).

Simple questions sometimes have complex answers.

Let's be logical for a moment. They already had a license for 125 watts ERP.

Your argument that "the old system may not be running it's maximum" is a smokescreen. If it was running less than 125 watts, the improvement made by the new 250 watt system would be even greater.

Your argument that "it's only a paper change, and they may not design the new system to the maximum on the license" is a weak one. They didn't make the FCC filing because they enjoy doing paperwork and paying filing fees. They did the FCC filing to license an improved station.

One excuse you forgot is the possibility that the station is already running at 250 watts, and this application is just an attempt to make it legal. In that case there will be no improvement in coverage.

But again, let's look at the title of the thread. It was a fairly simple question, and I answered it truthfully and correctly. You wanted to look smart by bringing up other issues relevant to coverage, and you did look smart.

So congrats.
 
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