A Ham Elmer wrote:
Someone asked:


I hear Hams exchanging numbers -- what do they mean?


During a contest, Hams exchange a combined signal report and a number - like
5906 -- the 59 is a signal strength and readability number URL:
http://www.cebik.com/rst.html

The basis for the S-unit is presumed to be as follows:

S9 corresponds to 100 microvolts "open-circuit"
from a 50 ohm generator. This corresponds to a 50
microvolt reading on the signal generator meter
scale. It also corresponds to -73 dBm in terms of
an "available power" level. The signal generator
scale markings coincide with this. Everyone seems
to agree about this much.

However, this does not mean that the actual signal
level into the receiver is 50 microvolts, because
we very seldom know the actual input impedance of
the receiver. Using "available" and "open-circuit"
we do not need to know the input impedance of the
receiver. The receiver is designed to operate from
a 50 ohm generator and that knowledge is sufficient.

The number of dB in an S-unit below the S9 level
is not, as many believe, guaranteed to be 6 dB per
S-unit. Different manufacturers have used numbers
as low as an "average" of 4 dB (Collins for
example). In vacuum tube receivers especially,
some latitude has always been necessary.

In my homebrew solid-state receiver (2003 design)
I use 5 dB because that correlates with the
"intuitive" evaluations that I have developed over
the years (that is my option for my personal
receiver). My S-meter, using precision circuitry,
is closely calibrated and marked based on accurate
sig gen readings. Also, my receiver gain does not
vary more than 1 dB across any ham band and 2 dB
from the 160 to 10 meter bands because of the way
the receiver is designed. This calibration is
quite stable and reliable. I check it frequently.

A picture of my homebrew receiver is on
QRZ.COM(W0IYH). Note the large high-quality analog
S-meter.

Bill W0IYH