[Elecraft] S-Meter Sensitivity

[k6se@juno.com]

Don, KD5NDB wrote:

"I have a Tektronix 191 leveled RF signal generator and a HP step
attenuator that goes down to 100 db. I set the RF level to 0.5 Volts and
the attenuator to 40 db giving 50 UV. With this connected to the K2 I
adjust the Cal S HI so the meter reads S9. This will usually come out
+or- a little from the manual set point."
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It sounds like Don was using the power ratio for dB, where a reduction of
10 dB is a reduction in power to 1/10, therefore a reduction of 40 dB is
a reduction in power of 1/10000.  However, it takes 20 dB of attenuation
to reduce the voltage by a factor of 10, therefore to reduce 500,000 uV
to 50 uV would require 80 dB of attenuation.  His 40 dB only reduced the
signal into the receiver to 5000 uV.

Someone else commented that the Tek 191 is calibrated in peak-to-peak
voltage, while S-meter sensitivity measurments are in RMS voltage.

So I guess Don should redo his S-meter calibration by setting his Tek 191
output to 14,142.27125 uV P-P (which is 5,000 uV RMS).  Then 40 dB of
attenuation would reduce the signal generator output to 50 uV.

If it took 5000 uV to make his S-meter read S9, his S-meter is stingier
than mine was, by far.

73, de Earl, K6SE
66 countries on K2 #2622 and counting.....