Marshall Amplification Field Marshall 100 Owner's Manual page 19

Distance Technique #1: Let's assume you are receiv-
ing a strong signal with the Range Switch on Far. Now
flip the switch from Far to Medium. If the signal remains
strong, it means you are fairly close to the transmitter.
With a strong signal, here are typical ranges to a trans-
mitter near the ground:
Near ............................Less than 200 feet
Medium........................About 1/2 mile
Far...............................Over 1/2 mile
The above table is only an example; you won't get the
same results. It depends on your transmitter, the ter-
rain, and many other factors. But over time you'll get a
feel for the distance these Range settings represent
with your transmitter and terrain.
Distance Technique #2: Just take a reading on the S-
Meter and then proceed in the direction of the transmit-
ter until the meter reads twice as much. You will have
covered approximately half the distance to your target.
This only works with direct line-of-sight signals of the
same polarization and gives only an approximation.
Still, it could save you from driving miles out of your
way. Adjust the Volume Knob during the first reading so
the meter reads about a third of full scale (where it is
likely to be the most linear.)
Ow ner's Manual
Page 19