Hello,

Does this seem logical?

1. The signal strength (example in dBm or mW) from a transmitting
source is measured.
2. Assuming most of the attenuation is due to free space loss, the free
space loss factor is "added" back to the measured signal to get the ERP
of that specific radiation lobe (it could be main, side, or back lobe).
3. The transmitter output is a known value (example 2 Watts).
4. Using the calculated ERP for a specific lobe, I can use the
following to determine the loss / gain due to the antenna & cable:
loss/gain = 10 log (transmitter output / ERP specific lobe).
5. If I rotate the transmitting antenna to 360 degrees, then I should
be able to have a rough picture of its azimuthal radiation pattern at a
certain elevation angle.

I'm probably using the terms the wrong way because I think ERP is
synonymous to the main lobe of the antenna (right?). But I'm just
treating the ERP as specified only to a certain lobe without knowing if
its the main, side, or back lobe.

I'm really not sure if this is right. I just want a confirmation
whether my logic is wrong, and if so, why? Thanks!

I think you make the issue too complex.

ERP = P[antenna]*[antenna Gain]

Example ERP = 400 Watts = [100 watts power]*[Gain of 4]; or,

ERP = 50 dBm + 6 dB(antenna) = 56 dBm = 400 watts.

Energy in the side lobe is then 56 dBm +[sidelobe in dB(antenna)].
Where the side lobe could be -20 dB yielding 36 dBm ERP in the side lobe.

MRW wrote:

Hello,

Does this seem logical?

1. The signal strength (example in dBm or mW) from a transmitting
source is measured.
2. Assuming most of the attenuation is due to free space loss, the free
space loss factor is "added" back to the measured signal to get the ERP
of that specific radiation lobe (it could be main, side, or back lobe).
3. The transmitter output is a known value (example 2 Watts).
4. Using the calculated ERP for a specific lobe, I can use the
following to determine the loss / gain due to the antenna & cable:
loss/gain = 10 log (transmitter output / ERP specific lobe).
5. If I rotate the transmitting antenna to 360 degrees, then I should
be able to have a rough picture of its azimuthal radiation pattern at a
certain elevation angle.

I'm probably using the terms the wrong way because I think ERP is
synonymous to the main lobe of the antenna (right?). But I'm just
treating the ERP as specified only to a certain lobe without knowing if
its the main, side, or back lobe.

I'm really not sure if this is right. I just want a confirmation
whether my logic is wrong, and if so, why? Thanks!

Hello Dave, Thanks! What if the antenna gain is not known? Would the
steps I mentioned be logical?