Math Check..

[DoWhat (Premo)]

Originally Posted by DoWhat

What is the wattage of the transmitter?

Frequency and receiver sensitivity are also a factor.

[itsbob]

Originally Posted by DoWhat

Frequency and receiver sensitivity are also a factor.

To get TO the range of 200 miles that is true.. BUT in this case I was looking for the minimum altitude where you could possibly pick up a target, or receive a signal independent of the signal strength.

We have more than enough power to go well beyond 200 miles, if the aircrew can keep the receiver working.

[SoMDGirl42]

Originally Posted by slotpuppy

Dont feel bad WR, your not alone.

I don't know math, but I do know the difference between your and you're. 180 degrees

[Railroad (Premo)]

Thank you, Wikipedia:

How much POWER do the GPS Satellites output on the 1575mhz L1 frequency?

One of our anonomous newgroup readers gave this correct answer..
In the frequency allocation filing the L1 C/A power is listed as 25.6 Watts. The Antenna gain is listed at 13 dBi. Thus, based on the frequency allocation filing, the power would be about 500 Watts (27 dBW).
Now, the free space path loss from 21000 km is about 182 dB. Take the 500 Watts (27 dBW) and subtract the free space path loss (27 - 182) and you get -155 dBW. The end of life spec is -160 dBW, which leaves a 5 dB margin.
And if you really get into it, you'll discover ALL of the following represent the same approximate signal strength for GPS on the face of the earth (m stands for milliwatts and m2 stands for meters squared):
-160 dBW, -130 dBm, -135 dBW/m2, -105 dBm/m2, -223 dBW/Hz, -163 dBW/MHz, -193 dBm/Hz, -198 dBW/m2/Hz, -138 dBW/m2/MHz Once you figure out why they're all the same, you're well on your way to understanding power, power density, and power flux density as it relates to GPS. For those that wish to quibble, I am assuming an even distribution of
power density over a 2 MHz C/A bandwidth.

[itsbob]

Originally Posted by Railroad

Thank you, Wikipedia:

How much POWER do the GPS Satellites output on the 1575mhz L1 frequency?

One of our anonomous newgroup readers gave this correct answer..
In the frequency allocation filing the L1 C/A power is listed as 25.6 Watts. The Antenna gain is listed at 13 dBi. Thus, based on the frequency allocation filing, the power would be about 500 Watts (27 dBW).
Now, the free space path loss from 21000 km is about 182 dB. Take the 500 Watts (27 dBW) and subtract the free space path loss (27 - 182) and you get -155 dBW. The end of life spec is -160 dBW, which leaves a 5 dB margin.
And if you really get into it, you'll discover ALL of the following represent the same approximate signal strength for GPS on the face of the earth (m stands for milliwatts and m2 stands for meters squared):
-160 dBW, -130 dBm, -135 dBW/m2, -105 dBm/m2, -223 dBW/Hz, -163 dBW/MHz, -193 dBm/Hz, -198 dBW/m2/Hz, -138 dBW/m2/MHz Once you figure out why they're all the same, you're well on your way to understanding power, power density, and power flux density as it relates to GPS. For those that wish to quibble, I am assuming an even distribution of

power density over a 2 MHz C/A bandwidth.

I've done the math before, not doing it right now, but if I remember right it was like 1.8x10^-13, or about two billionth of a watt.

[Railroad (Premo)]

Originally Posted by itsbob

I've done the math before, not doing it right now, but if I remember right it was like 1.8x10^-13, or about two billionth of a watt.

Really quite incredible, when you think about it. Lots of people don't realize how tenuous their hold is on a "reliable" navigation system.