Radiated power measurements

Thread Starter


Joined Apr 22, 2008
I have a HF transceiver transmitting at roughly 9MHz and 20dBm into a active monopole antenna. i would like to try and measure the radiated power from the antenna. Traditionally i would subsitute the DUT for a known source and measure the air gap losses. would this still work even though im measuring in the near field? how is ERP normally measured? i would also like to do the reverse and try and measure radiated receiver sensitivity.


Joined Feb 29, 2020
This sounds straight forward but is really complicated in so many ways. ERP is measured on a range at some distance and includes the transmitter antenna gain- a low power transmitter with a lot of antenna gain could have an appreciable ERP. The antenna also has a specified pattern, high gain antennas usually have a lot of narrow lobes and discontinuities in the near field. ERP is generally not meaningful in the near field- the field isn't a plane wave in the near field. Real ERP measurements like these are generally done at far field- maybe 100 lambda- which would be something like 3 kilometers at 9 Mhz. You might consider something like the reverse beacon network that hams use to watch propagation. They receive signals and post them to the internet with signal strength. I probably need to know a bit more about your application. I worked on a tracking project in the HF spectrum to track birds worldwide with low power HF transmitters. Its a tough problem. I really don't understand your receiver sensitivity question but its a similar issue with antenna patterns getting convolved into the mix. Luckily most of this stuff is reciprocal and things work similarly whether you're transmitting or receiving at least from a Friis equation level- what I think you're calling "airgap".