External receiver calibrators are available as Elecraft kits XG1 and
XG2. They provide an output of either 50uV or 1uV into a 50-ohm
resistive load. These levels correspond to S9 and S3 1/3 per the IARU
Region 1 recommended standard. But how many receivers provide a 50-ohm
resistive input (without an input attenuator switched in)?
The actual applied voltage depends also on the output impedance of the
test oscillator, but that should be very close to 50 ohms resistive
because the output attenuator of the XG1 is 23 dB for the 50uV output,
and another 34 dB for the 1uV output. The XG1 was reviewed in April
2005 QST. The review includes some discussion of receiver S-meter
performance.
73, Tony W1OT
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