Elecraft XG2 Manual - Manual (Page 7)

7
Many factors can affect the S+N and N readings, including whether a KSB2 or KNB2 is installed,
which band is selected, how the band-pass filters and BFOs are aligned, how L34 is adjusted, and
whether the 2nd XFIL modification has been made (already present in K2s with S/N 3000 and
higher). If the estimated MDS value is lower than expected, make sure that you have the preamp
on, AGC off, ATU in bypass mode, and RF GAIN set fully clockwise.
A K1 should produce a S+N (XG2 on) reading of roughly 0.1-0.2 Vrms, and an MDS of about -
130 dB.
S-Meter Calibration (Using 50 µV Signal)
50 microvolts is widely used as the standard for an S-meter reading of "S-9". The manufacturer of
your receiver or transceiver may prefer a different level; consult its manual. Also note that S-
meter readings are relative. On some transceivers, including the Elecraft K2, turning the preamp
off or the attenuator on will drop the indicated value. (The K1 adds one bar to the reading if the
attenuator is turned on.)
To align your S-meter at 50 microvolts:
1. Set up the receiver or transceiver as indicated in steps 1-13 on the previous page. In this case,
there's no need to turn AF GAIN to maximum.
2. Turn the AGC on (K2, hold PRE+AGC switches. K1, use AGC menu entry).
3. Switch the XG2 to its 50-microvolt setting.
4. Adjust the S-meter "scale" value such that the S-meter indicates S-9. (K2, use CAL S HI
function. K1, use SIG menu entry, "H" parameter. The K1 does not have a labeled S-meter scale;
use 4 bars for S-9.)
5. Turn the XG2 off. The S-meter reading should now drop to approximately zero (1 bar may be
flickering on/off). If not, adjust the S-meter's "zero" value. (K2, use CAL S LO. K1, use SIG, "L"
parameter.) Repeat steps 4 and 5 if necessary.
Circuit Description
The XG2 produces a signal at with very accurate amplitude. Unlike most signal generators
capable of accurate 1-µV output, the XG2 requires no shielding. This is due to the extremely low
power level of the crystal oscillator, as well as careful PC board layout and component selection.
The output of the oscillator (-50 dBm or 10 nanowatts into 50 ohms) is attenuated by 23 dB to
obtain the 50-µV test signal. An additional 34 dB attenuator stage is placed in series with the
signal path by switch S2 when an output level of 1 µV is needed. Output accuracy is determined
by the precision voltage regulator and 1% resistors.