Question about Power...

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btritch

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Hey, I have a question, I have been looking up licenses on the FCC ULS Database tonight and I have a question, What does the Output Power and the MAX ERP power mean, I know it's the Maximum Effective Radiated Power, But what's that mean, That it's the most they're allowed to run... and The Output Power is the amount They Are running, Right?
 
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zz0468

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Output power is the actual RF output of the transmitter. ERP is the transmitter power multiplied by the antenna gain, minus any feedline, duplexer, or combiner loss.
 

btritch

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Output power is the actual RF output of the transmitter. ERP is the transmitter power multiplied by the antenna gain, minus any feedline, duplexer, or combiner loss.
So when wanting to know what a department put out, Which should you go by, the ERP or the output power?

Also, If it reads 40.00, Does that Mean 40 Watts?
 

prcguy

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Its the radiated power from the antenna taking the transmitter power, antenna gain, feedline and other losses into account. It is usually written as EIRP which references antenna gain to an Isotropic radiator or 2.14dB less than a dipole. If you had say a 50w transmitter, a 10dbi gain antenna and 3dB of losses between the transmitter and antenna, you would have 250w EIRP. If the antenna had 10dBD gain the EIRP would be 2.14dB higher. I don't have a calculator with me but the EIRP in that case would be around 350-400w.
prcguy
Hey, I have a question, I have been looking up licenses on the FCC ULS Database tonight and I have a question, What does the Output Power and the MAX ERP power mean, I know it's the Maximum Effective Radiated Power, But what's that mean, That it's the most they're allowed to run... and The Output Power is the amount They Are running, Right?
 

KC0QNB

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A transmitting antenna with gain will increase the ERP, since there hasn't been anything made to output over 100 watts in some time, the erp would be the theoretical actual output power that is at the antenna after the gain has been added.
look at this for a better explanation
Using the chart I posted the link to, my 50 watt mobile IC-2100H connected to a 3dB antenna would have an ERP of 105 watts, double my output and then some.
 

btritch

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So to see how much power a department is putting out after all of that is done, their actual output power, I should go by their ERP power, What they're actually transmitting is the ERP, Not the output, Correct?
 

prcguy

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Without referencing the antenna gain to a dipole or isotropic radiator, the end result is just a relative number.
prcguy
A transmitting antenna with gain will increase the ERP, since there hasn't been anything made to output over 100 watts in some time, the erp would be the theoretical actual output power that is at the antenna after the gain has been added.
look at this for a better explanation
Using the chart I posted the link to, my 50 watt mobile IC-2100H connected to a 3dB antenna would have an ERP of 105 watts, double my output and then some.
 

zz0468

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So to see how much power a department is putting out after all of that is done, their actual output power, I should go by their ERP power, What they're actually transmitting is the ERP, Not the output, Correct?
It depends on what you want to do with the information. If you just want to know how powerful the transmitter is, then the transmitter power output listed on the license will tell you. If you need to do a path budget to determine how strong you can expect the received signal to be, then you need to know ERP, and a whole lot more.
 

KC0QNB

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Without referencing the antenna gain to a dipole or isotropic radiator, the end result is just a relative number.
prcguy
Hey I just read the chart, I tried to find the actual formula for the calculation, but no luck yet, one site I found a calculator on also references the frequency as a factor.
 

kb2vxa

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Let's not muddy the water by bring isotropic into it when it's completely irrelevant, dBd has been the standard of the industry all along. They're not fooled by dBi that came along to trick CBers into thinking a Super Starduster is like putting a 100W "leenyar" on a ground plane.

There is much more to the equation than previously stated including height above average terrain; for example 10KW ERP at street level becomes 50KW 1,250 feet atop Empire in New York. Er, an engineer for ABC told me that. (;->)
 

zz0468

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There is much more to the equation than previously stated including height above average terrain; for example 10KW ERP at street level becomes 50KW 1,250 feet atop Empire in New York. Er, an engineer for ABC told me that. (;->)
The ERP would stay the same, regardless of the elevation above ground. What changes is the service contour. And I think you may have that backwards. A 50kw ERP transmitter at ground level would have a contour more like 10kw at 1250 feet agl.
 

n2mdk

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Let's not muddy the water by bring isotropic into it when it's completely irrelevant, dBd has been the standard of the industry all along. They're not fooled by dBi that came along to trick CBers into thinking a Super Starduster is like putting a 100W "leenyar" on a ground plane.

There is much more to the equation than previously stated including height above average terrain; for example 10KW ERP at street level becomes 50KW 1,250 feet atop Empire in New York. Er, an engineer for ABC told me that. (;->)
That wouldn't have been Steve "the sky is falling" Mendelsohn w2ml would it.
 

prcguy

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I work with satellite and terrestrial microwave link budgets with the FCC and EIRP is the standard. All gain figures for antennas on FCC licenses are listed in dBi. All applications for new terrestrial microwave licenses (in certain bands) within 75mi of my work pass through my desk and its all EIRP and dBi. Were not foold by an old CBer who doesn't know the relevance and importance of gain referenced to an isotropic radiator, its a standard just like dBD.
Height affects propagation in a terrestrial link but I have not seen it compensated for in FCC licenses. The affect is caused by ground reflections where the direct and reflected wave arrive at the antenna out of phase and cause some cancellation which can range from about 6dB to as much as 20dB. Having one of the antennas at a high point increases the angle of reflection and can reduce the cancellation. This is why you cannot use free space loss calculators for VHF/UHF or HF radio links without estimating phase cancellation losses. With lower frequency antennas (VHF/UHF/HF) you also have ground effects pushing the pattern upward and raising the antenna can pull the main lobe down where it fills in at the horizon. When people put up a very large yagi say for 6m and only have it 20ft off the ground, that fat 10dB of gain it has is being wasted at a high angle and never reaches the horizon, it needs to be up 80 or 100ft to get the lobe back down.
prcguy
Let's not muddy the water by bring isotropic into it when it's completely irrelevant, dBd has been the standard of the industry all along. They're not fooled by dBi that came along to trick CBers into thinking a Super Starduster is like putting a 100W "leenyar" on a ground plane.

There is much more to the equation than previously stated including height above average terrain; for example 10KW ERP at street level becomes 50KW 1,250 feet atop Empire in New York. Er, an engineer for ABC told me that. (;->)
 

key2_altfire

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Without referencing the antenna gain to a dipole or isotropic radiator, the end result is just a relative number.
Isn't the "i" in "dBi" for "isotropic"?

(Just for those who don't know:)

dBm = dB referenced to "m"illiwatt. 0 dBm = 1 mW
dBW = dB referenced to "W"att. 0 dBW = 1 W
dBc = dB referenced to "c"arrier. 60 dBc = 60 dB BELOW carrier (so this is actually a number to indicate negative gain)
 
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