"MRW" wrote in news:1172850043.053869.294430@
30g2000cwc.googlegroups.com:

Good morning!

I would like to request some additional info regarding the following
matter.

Is there a way to approximate the antenna factor loss (in dB/m) for an

The word loss does not belong in there.

x-length (in inches ... maybe 26 inches) regular telescoping, monopole
antenna that will be subjected to frequencies between 88-108MHz (FM
band) at a height between 2ft to 15ft from the ground?

Simple formulas to determine AF depend on the monopole being short (and
yours isn't) and on a perfect ground plane (you haven't stated).


Here's the scenario. A 50-ohm receiver will be used. A cable with an
insertion loss of 1.5dB will also be used. The receiver has
sensitivity levels as low as -5 dBuV. The lowest received signal that
we want to measure is 100uV/m.

You would be best served by converting your minimum Field Strength to
received power for a nominal antenna system, then determining the minimum
antenna system gain that will achieve your target S/N ratio (not stated
in your data, sort of implied in your sensitivity spec, but check /
adjust it).

With a antenna *system* gain of 0dBi, at 108MHz with FS 100uV/m
(40dBuV/m), the 50 ohm receiver voltage is 29.1 dBuV. The receiver
voltage will 30.9 dBuV for the same situation at 88MHz.

From the above, the Antenna Factor for a 0dBi gain at 108MHz is 40-29.1=
10.9dB/m, and yes, it is frequency dependent.

Antennas aren't often specified by Antenna Factor, gain is more common.

Antenna system means all components upstream of the receiver.

Owen