Elecraft XG3 RF - Manual (Page 15)

15
Receiver Testing
You will need a way to connect your XG3 to the receiver to be tested. Most receivers have either a BNC or
SO239 (UHF) antenna jack. A male-to-male BNC adapter is available to connect the XG3 directly to a
BNC jack on the receiver (order BNC-MM from the Elecraft web site).
Measuring Receiver Sensitivity
This procedure measures absolute receiver sensitivity, allowing you to confirm that your receiver is
operating as expected or for comparing receivers. If you make these measurements in advance, you can
easily check to see if your receiver performance has degraded over time, especially after exposure to
lightning or other traumatic events.
You will need a DMM capable of measuring the AC audio output level of your receiver at the speaker or
headphones jack. A true RMS meter is ideal, but a common DMM will result in only a small error of about
1 dB. (If you have an Elecraft K3, a true RMS audio voltmeter is built in. See VFO B Alternate Displays in
your K3 Owner’s Manual.) Also, you’ll need to do some logarithmic calculations. You can use any
calculator with a “log” function key including the scientific calculator built into most Windows operating
systems under “Accessories” (after opening the basic calculator you may have to select “View/Scientific”).
The procedure is done in two parts. First you’ll collect data from the receiver using your XG3. Secondly
you’ll calculate the Signal-to-Noise plus Noise (S+N/N ratio) with a standard 1 µV test signal and estimate
the Minimum Discernable Signal (MDS).
Collect the data as follows:
1. If working with a transceiver that has a built-in antenna tuner (ATU), put it in bypass so it
is no longer in the circuit.
2. Connect the XG3 to the receiver’s antenna jack and turn the receiver on.
3. Set the receiver controls as follows:
AGC Off If possible.
RF Gain Maximum (if adjustable).
Attenuator Off If present.
Preamp On If present.
CW Mode
I.F. Bandwidth 500 Hz, if adjustable. This is the standard for lab receiver tests.
Audio Filter If present, set for widest possible audio bandwidth.
4. Connect your DMM across the loudspeaker terminals or, if necessary, across the headphones jack.
If you use the headphones jack, do not plug headphones in at the same time to avoid reducing the
available audio voltage.
5. Turn on the DMM and set it to read AC voltage on a low range (probably 2 to3 VAC maximum).