On 23 jun, 05:22, "George" wrote:
What's the easiest/fastest way to calculate received power out of a very
short non-resonant antenna? Frequencies are in the HF and VHF ranges, TX
powers in the kilowatt range, and distance from transmitting antenna a few
miles. Thanks for any help.

George K6GW

Hello George,

I think this question relates to a previous posting regarding power
extraction?

First step is to find path attenuation.

Second step is to convert the Fieldstrength to EMF out of your
antenna.

Third step, converting EMF into power.


You may use ITU propagation curves for frequency planning or use two-
ray propagation formula as a ballpark.

EMF out of your antenna (optimal orientation) will be about
0.5*Efield*length.

The capacitance of your whip will be about some pF. This limits the
available power (non resonant).

Example:

A broadcast transmitter (100 MHz) with ERP = 10kW produces about 30mV/
m at 3 miles and h=5 ft.

This would produce about 4.5mV out of your whip.

When we assume that the capacitance with respect to the ground plane
is about 5 pF (-j320 Ohm), you may extract about 32nW of AC power
(without resonance).

When the antenna has no descent "counterpoise" and / or is not
oriented optimal, the output will be significantly less. Terrain
features will also affect output power.

Hope this will help you a bit,

Wim
PA3DJS
www.tetech.nl