[Icom] S-Meter Units

[Tim Duffy K3LR]

Here is my S meter experience with the 781 and 765. I always set S9 for -73 dBm
(50 uV) without the pre amp on. The S meter is very well calibrated above S9
when aligned this way. So every 10 dB increase in signal tracks perfect up to
+60 which is -13 dBm. The only other data set point I use is the signal strength
required for the meter to come off the left hand peg (S0) which is anywhere
between -95 and -102 dBm depending upon the radio and the overall gain settings.

S0 to S9 is the land of uncalibrated.

73!
Tim K3LR

Floyd Sense wrote:

> 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
>
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