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I am building several types of radio antennas, and I would like to test which is the most effective. I am wondering: What is the best way to measure the strength of the received signal?

It is at ~151 MHz and 2 watt transmission power, and I will be testing over a distance of at least a couple of hundred feet. The results don't have to be calibrated, only correct relative to one another. Any ideas?

Thanks in advance

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For antennas, it's often interesting to know at which frequencies they work best and how far that is from the frequency you designed them for.

So, if you have a broadband or adjustable tone transmitter, you can just plug your antenna into an RTL-SDR dongle (cheap!!) and observe the received spectrum.

That'll not only give you relative reception strength at a given design frequency, but also an understanding for which bandwidths the antenna works well.

Note that passive antennas are reciprocal - i.e. what works good as receiver works just as well as a transmitter; this means you can swap the roles of transmitter and receiver, if that makes the measurement system easier.

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  • $\begingroup$ The SDR dongle is a great idea! Exactly what I have been looking for. Thanks! $\endgroup$ – Danny Feb 27 at 15:38
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You could use a receiver with an S-meter or if you are not too close to commercial RF signals you could use a field strength meter.

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Considerations when comparing the field intensities from different transmit antennas over a given terrestrial path, and assuming use of the same receive+antenna system and its siting/adjustment for all measurements:

  • Path distance from transmit antenna to receive antenna
  • Height above the reflecting plane (Earth) of the radiation center of each transmit antenna
  • Free-space radiation pattern of each transmit antenna toward the receive antenna, in the vertical plane

The graphic below shows the variations in received field vs. elevation above a level ground plane, for the configuration and conditions stated in the graphic.

The vertical axis (Z) = Height above Earth of the calculated field.

The horizontal axis (E) = Field intensity in mV/m.

enter image description here

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