Measuring rf power around 300 MHz

Discussion in 'General Electronics Chat' started by mj3, Apr 19, 2016.

  1. mj3

    Thread Starter New Member

    Apr 19, 2016
    Hi all,
    I'm trying to measure the power of an rf signal that frequency ramps over 200-400 MHz. My signal strength as measured on a spectrum analyser is around 0 dBm (into 50 Ohms) post-amplification (expects 50 Ohm load), but I'd like to know the total power in this band without requiring the analyser. Ideally I'd be able to measure Vrms or an associated quantity.

    Naively I considered rectifying the signal and charging a capacitor, but given the high frequency and (relatively) low amplitude of the signal I'm not sure this would work. Is there any "obvious" solution to this besides purchasing test equipment?

  2. Papabravo


    Feb 24, 2006
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    If you can measure then get rms value with either a scope or a high impedance volt meter you will get a very close approximation of power levels
    Most of the error between theory and practice will be due to inefficiency of antenna matching. High SWR is a real Watt killer.
  4. mj3

    Thread Starter New Member

    Apr 19, 2016
    Unfortunately I don't have a scope with high enough bandwidth to directly see the rf, which is why I'd like to convert it to a power measurement. I'll check out the Wattmeter, but would something like the AD8361 or MAX2014 be a cheap solution?
  5. MikeLogix

    New Member

    Mar 1, 2016
    I don't think a Bird watt meter can measure the small amplitude signal (0 dBm) as stated by mj3. The Bird meter requires at least 100mW.
  6. dannyf

    Well-Known Member

    Sep 13, 2015
    Try logarithmic amplifiers. Analog has a few of them. 8307 for example.