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I own several spectrum analyzers and build various RF boards at all kinds of frequencies.

I was looking over a BLE FCC test report for emissions, and I saw this lab uses a RF power meter to measure the output of the system.

Why would you not use a spectrum analyzer for this?

Why does an RF Power meter even exist? Is it simply because it is cheaper than the spectrum analyzer?

Can anyone weigh on the rationale for an RF power meter?

I'm looking at this very expensive looking RF power meter, and it seems like just a spectrum analyzer that sweeps over frequenicies:

4500C Peak Power Analyzer

I understand the smaller handheld RF power meters probably just take average readings of power without the frequency sweeping?

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  • \$\begingroup\$ They exist because it wasn't always possible to build an inexpensive spectrum analyzer. And, a lot of times, all you really need is the power of a band rather than at some particular frequency. \$\endgroup\$ – JRE Jul 28 '18 at 15:46
  • \$\begingroup\$ Also, spectrum analyzers are calibrated against power meters in the factory. \$\endgroup\$ – Simon Richter Jul 28 '18 at 17:24
  • \$\begingroup\$ You have it the wrong way around. A spectrum analyzer is (or was) a power meter with a tuner in front that sweeps over frequencies. \$\endgroup\$ – The Photon Jul 28 '18 at 21:12
  • \$\begingroup\$ @The Photon, I know this is kind of your space. Is there any reason why you would buy a power meter with current spectrum analyzers? I can see from an EMI lab, having one to open up more timing in the shielded chamber for compliance testing. Any other reason? (Speaking of cheap spectrum analyzers, I have a 7GHz project coming in and really am thinking of trying one of those sketchy Chinese USB spectrum analyzers. A legit 7GHz spectrum analyzer is not cheap...). \$\endgroup\$ – Leroy105 Jul 29 '18 at 14:26
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    \$\begingroup\$ Also, power meters generally measure the average power over their full measurement bandwidth, no conventional spectrum analyser can do this as they effectively sweep a narrow (RBW) filter across the band at a fairly low rate. A good thermocouple power head will have a fairly flat response from maybe 10MHz to 4GHz and will have maybe 70db or so of average power dynamic range, with maximum 1us short term performance maybe 20dB higher then the average. Different tools for very different jobs. \$\endgroup\$ – Dan Mills Jul 30 '18 at 16:21

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