LF: Fieldstrength and radiated power

[Markus Vester <markusvester@aol.com>]

Dear LF,

 

to support estimates of radiated power, I have added a fieldstrength readout on my LF grabber

 

 http://www.alice-dsl.net/df6nm/grabber/Grabber.htm

 

It simply displays the peak frequency and amplitude within the QRSS subband at the time of the capture (ie. every five minutes). Due to different calibration issues, the readout will be accurate only to within about 3 dB. There may also be considerable day-to-day variation, for example from switching between different receive antennas.

 

In the region of groundwave dominance (up to 400 km daytime, 200 km in darkness), radiated power in dBm or milliwatts can be roughly estimated based on distance R using

 

 EMRP[dBm] = 20 log E[uV/m] + 20 log R[km] + 0.02 R[km] - 49.5

 EMRP[mW] = 10^(EMRP[dBm]/10)

 

To convert to halfwave-dipole ERP or EIRP, you would have to apply the usual factor of 1.83 or 3.

 

Hope this may be useful...

 

Best 73,
Markus (DF6NM)