[Icom] S-Meter Units

[Floyd Sense]

While working on another project where I had my signal generator connected
to the 765's SO-239, I decided to see how the S-meter's S-Units actually
measured. You might find the results interesting. As you'll see in the
following, an S-unit equates to the commonly stated 5-6dB only over a very
narrow range. The scale is VERY non-linear, particularly at the bottom end.
The generator I used is an old commercial Boonton 103F, which is similar to
the 103D, and it includes a calibrated attenuator. In the following, the
change in signal strength required to raise the S-meter reading to the next
unit appears between the two units.  It's possible that a 1 dB anomaly as
seen between S1 and S2 was caused by having to switch attenuator ranges on
the generator and readjusting the output.  I don't know what the claimed
accuracy of the attenuator is.

S0

  2.5 dB

S1

  1.5 dB

S2

  2.5 dB

S3

  3 dB

S4

  5 dB

S5

  5 dB

S6

  9 dB

S7

  8 dB

S8

  10 dB

S9

  8 dB

+10

  11.5 dB

+20

  11.5 dB

+30

  15 dB

+40

  11.5 dB

+50

  6.5 dB

+60



As you can see, "a couple of s-units" on the 765 could be anywhere from 4 dB
to 18 dB - quite a difference!

73, Floyd - K8AC