Calculating "Total" Power for attenuation needed... A few of us needs to know this and I need to know if I'm on the right track. I'll use my set-up for an example.
What I have and want to test:
P4 controller - .303W
Sunhan booster - 3W
Maxxrange antenna - 14db or .025W (?)
Total watts = 3.328 or 35.22dBm (actual attenuation needed)
So, 40dB worth of attenuation would suffice? Am I on the right track? If not, could you explain as simple as possible? I understand now it's all Log scale and not linear, but wanted to check with you guys about adding controller and antenna being used to the equation.
Thanks in Advance.
JB
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There is a bit more to it. It's more involved than a direct measurement of RF power....
ERP, or effective radiated power, is a more relevant measurement of system output power. Example: a bare light bulb radiates evenly in all directions (I know, it doesn't radiate where the electrical connection is made). Put a reflector behind the bulb and the reflector concentrates the light in a single direction. If you wanted to measure the light output of a flashlight you wouldn't be particularly interested in how bright the bulb is. You would be more interested in how bright the flashlight is in the direction it's pointed in.
It's the same thing with RF. Transmitter power is a single component of RF measurement. ERP is a combination of transmitter power, and how the antenna concentrates radiated energy in the intended direction. This how an antenna system can have gain.
Example: an antenna with, say, 5dB of gain gets that gain by concentrating RF power in the intended direction(s). The ERP will be a combination of RF power output at the transmitter, and the gain the antenna system concentrates in the intended direction. Other factors come into play, such as antenna HAAT (Height Above Average Terrain), but for most of us, HAAT doesn't factor in.
The reflector of a flashlight concentrates light in the direction the flashlight is pointed. The bulb only gets so bright, there is only so much radiated light to work with, so the flashlight concentrates light in a single direction at the expense reduced light emitted at the rear of the flashlight. It works exactly the same with RF power measurements.
My P4 RC has a pair of antennas. Assuming that both antennas radiate energy (which makes sense) and if the spacing between antennas is correct, an unmodified RC will radiate more energy in the forward direction, and in the direction behind me. Because of this, if both antennas are radiating, the resulting antenna array will have some gain. I'll assume this is the rationale for DJI using a pair of antennas.
For all I know, only a single antenna radiates. The other antenna may be there just for show.
I could be wrong about this, but I doubt that one antenna is used for transmission, and the other antenna is used for reception, as I have heard out here. It's because transmission and reception don't occur at the same time. Instructions go from the RC to the bird, then it's the bird's time to transmit. It's a back-and-forth type of communication.
The most honest way to measure ERP is either by use of a field strength meter, or by implementation of some truly gnarly math. Me, I'll use the field strength meter...
So there, that's my $.02
Cheers