I am running a software radio application. I need to measure the power of transmitted ofdm signal. The issue is that FCC has regulations of -50dBM/Hz. So I understand that if i need to send a signal at a bandwidth of 1Mhz, the the maximum allowed power -50dBM*10^6 which is 0.01W or 1mw.So i am trying to measure the power at output of my USRP transmitter. I just brought an oscilloscope and measured the sinusoidal signal peak to peak voltage in the oscilloscope. It was 7.2 v peak to peak. I was unsure how to use v^2/R because i don't know the resistance. when i assumed resistance to be 1, I got the power output to be 39dBM. I then checked online and found that you need to measure power spectrum. So that means I need to know power at frequency of transmission. I need a RF power analyser for the same. How is the power at frequency spectrum related to analog power measured by oscilloscope at the output of antenna? What should i measure and reduce if i need to keep it within desired FCC regulations? Is the power of the frequency spectrum constant?
- A RF anechoic chamber (wedges on the walls, floor and ceiling to prevent any reflections)
- A test device with an antenna and physical setup (construction, mounting, form, shape etc.) that's very close to what you want to ship
- A calibrated measurement setup, that's typically multiple receive antennas in the chamber or a full 3D setup (vertically movable antenna plus a horizontal turn table)
- Very good understanding of the polar pattern of your transmit antenna
- A good calibrated spectrum analyzer
- Time & patience
This is not an easy measurement to make, so most companies farm that out to certified test houses, who have the equipment, facilities and experience to do this.