"William E. Sabin" wrote in message
...

"Avery Fineman" wrote in message
...
Is there a standard RF input level per "S" Unit?

If so, please post the location. Thanks.


My homebrew solid state receiver (see QRZ.COM) uses 5 dB per S-unit. S9
corresponds to -73 dBm available power, which is 100 microvolts
open-circuit from a 50 ohm sig gen, or 50 microvolts into a 50 ohm load.
Available power and open-circuit voltage are used because the input
inpedance of the receiver is not guaranteed to be 50 ohms. I use 5 dB per
S unit because it compresses the scale a little and it also agrees more
closely with the intuitive listening test measure that I have used for
many years. The upper end of the scale is 30 dB above S9, which is -43
dBm, a very strong signal. Signals stronger than S9+30 dB I don't bother
to measure. At S1 the signal level is -73 - 40 = -113 dBm. Signals weaker
than that S1 I don't try to quantify.

My receiver has a low noise RF preamp with 8 dB of gain that I use on the
12 and 10 meter bands, when those bands are quiet. This makes the S meter
less accurate but I don't worry about that. To get an S meter reading I
turn off the preamp briefly.

My receiver has a custom made, computer printed scale using a calibrated
sig gen, and there are two trimpot adjustments, one for the low end and
one for the high end. This circuit uses voltage regulated opamps. The S
meter dynamics are adjusted using RC time constants.

My S meter is accurate within +/- 2 dB from 160 M to 10 M, because the
receiver is designed for this accuracy. Because of the IF and RF circuit
design, the scale calibration is fairly correct and reliable, as I
mentioned.

Bill W0IYH


My receiver also has a 20 dB antenna input attenuator that can be switched
in from the front panel. This extends the upper signal range to S9 + 50 dB.
I use it very rarely.

Bill W0IYH