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I am an engineering co-op tasked with measuring the output power of an avionics WiFi unit. I want to measure the maximum conducted power at the coax port to then calculate max EIRP.

The challenge is measuring the WiFi signal itself. I am using a Tektronix RSA306B and SignalVu (Not the full subscription, so I don't have the WLAN measurement tools).

I decided to go with the MAX value shown on the Amplitude-vs-time measurement as it was the closest to the datasheet for the WLAN chip that is in the unit. Is this right?

For clarification the mode(s) measured are 802.11b/g.

On another Avionics unit, I tried measuring the integrated power as I read somewhere that that's the power you want to measure, but I kept getting outrageous values that exceed the WLAN chips datasheet values.

I obviously have no idea what I am doing here, so any help with pointing out the best way to measure the maximum conducted power of a WiFi signal would be fantastic. Additionally, if possible, I would like to know what exactly the Amplitude-vs-time measurement is measuring if the peak of the spread spectrum signal is at -20dBm and the A-vs-T measurement is measuring 13.33dBm.

The measurements I made on Avionics Unit A (one screenshot of many similar shots): SignalVu Screenshot WLAN Measurement

The measurements I made on Avionics Unit B (one screenshot of many similar shots): enter image description here

Edit1:

  • I am aware of the two different RBW values.
  • Unit A and Unit B have two different WLAN chips.
  • The setup was calibrated and cable loss is accounted for.
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  • \$\begingroup\$ 1st, calibrate your setup. Use an RF signal generator, with a known attenuator and measure it. 2nd, use the same RBW across all measurements. One of your measurements uses 10KHz, the other 5KHz. It can affect the amplitude measurement. \$\endgroup\$
    – Lior Bilia
    Nov 21, 2023 at 18:23
  • \$\begingroup\$ @LiorBilia The setup was calibrated and cable loss was accounted (should probably mention that, thanks!). I am aware of the change in amplitude based on RBW, the two units have different WLAN chips in them. But you are right, RBW is one issue here. There is a bit more to my question then that unfortunately. \$\endgroup\$
    – Pxl
    Nov 21, 2023 at 18:27

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I have asked some knowledgeable co-workers, and the answer they provided is as follows:

  • Amplitude vs. time is fine for measuring the peak conducted output power.
  • Integrated power (or channel power) will be greater than your peak as the total power is spread across the signal (channel bandwidth).
  • Amplitude vs. frequency will give power over the spectrum.
  • The RSA is an FFT device, amplitude vs. time will sum all the spectral components in the time domain, which is the same as a Zero Span measurement over the spectrum analyzers set capture bandwidth.

So for those wondering, to make a Zero Span measurement on the Tektronix RSA306B and SignalVu software, make an Amplitude vs. time measurement and set the Span (capture bandwidth) as your desired signal bandwidth.

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