Elecraft XG2 Manual - Manual (Page 6)

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the same time, since this will form voltage dividers with R35 and R36, lowering the AC voltage
reading.)
11. Set the receiver or transceiver for about the XG2 output frequency that you have selected.
12. Turn on the XG2 and set it for 1 microvolt output. Replace the battery if the power-on LED
does not light.
13. Locate the XG2 signal with the receiver. Peak the signal in the crystal filter passband.
NOTE: BFO settings can affect sensitivity. If the passband peak occurs at a pitch well outside the
expected range (typically 500-800 Hz), you may need to realign your BFO settings using an
appropriate method (K2: see application notes on our web site).
14. Set the AF GAIN control fully clockwise (if this results in a signal that is loud enough to
damage the speaker or cause distortion, use a reduced setting, but make sure you use the same
setting each time).
15. Note the DMM's reading: _______ Vrms (this is the S+N, or signal+noise reading). NOTE:
This value is useful for comparing overall receiver gain with that of a reference receiver.
16. Turn off the XG2 and note the new reading: _______ Vrms (this is the N or noise reading).
Signal-to-Noise And MDS Calculations
Using the results from the previous page, you can calculate the signal-to-noise to noise ratio
(S+N/N) at 1 microvolt, and estimate the MDS (minimum discernable signal) as follows:
A. Divide S+N by N; call the resulting ratio R.
B. Take the base-10 logarithm of R ("log" key on most calculators).
C. Multiply the result by 20 to obtain the S+N/N ratio at 1 microvolt, in dB.
D. If the S+N/N is greater than 10 dB, then the MDS is approximately
equal to the result from (C) subtracted from -107 dBm.
Example: DMM readings of 1.0 Vrms (XG2 on), and 0.030 Vrms (XG2 off).
A. R = 1.0/.03 = 33
B. log(33) = 1.52
C. 20 x 1.52 = about 30 dB (this meets the requirement for step D)
D. MDS = -107 dBm - 30 dB = -137 dBm
A K2 should produce a S+N (XG2 on) reading of roughly 0.4-0.8 Vrms, and more importantly,
an MDS of about -135 dB or better. With an audio filter installed, the S+N and N readings may
be higher, especially if you've modified the gain settings, but the MDS should be about the same.