Connecting cables.
w.2.2. Test Setup
The illustration below shows the test setup. The headphones let you listen to the
receiver audio at the same time you measure the level.
Caution: Before you connect your transceiver to the signal generator, render your
transceiver unable to transmit by disconnecting the MIC and KEY. You will be irked, to
say the least, if the attenuators in your signal generator are smoked by a brief burst of
power out of your transceiver.
w.2.3. Test Methodology
If your signal generator is not synthesized or phase locked, let it warm up thoroughly.
Make the connections in the test setup shown above.
For each band you wish to measure (and each mode), repeat the following steps:
1. Set the receiver to the desired mode. Set the RF gain control to maximum.
2. Set the signal generator for a test frequency in the band and set the receiver to the desired
mode. The signal generator should be in CW mode, i.e., no modulation. Assume we start in
the 40 meter band. I set my signal generator for 7250.00 KHz. The signal generator output
level should be at approximately -100 dBm. (2 uV if your signal generator is calibrated in
microvolts) Tune the receiver to the signal generator frequency and verify that you can hear
it.
3. Tune the receiver away from the signal generator 10 or 15 KHz. You should not hear the
signal generator in your receiver; to test this, unplug the coax cable connecting the
generator to your receiver. You should see no significant change in the voltmeter and you
should hear no significant difference in audio output. (connect the cable back, of course.)
4. Keeping the receiver's RF gain at maximum adjust the AF gain to provide a low but
comfortable listening level (e.g., .01 VAC). Record the voltmeter reading.
5. Tune the receiver to the generator frequency, adjusting the receiver frequency so that the
audio output as read on the voltmeter is maximized. Do not adjust the receiver audio level!
6. If your voltmeter reads in dB, vary the signal generator's output level (should need to be
reduced if you started at the recommended -100 dBm level) until the audio level is:
10dB above the noise reading (equals 3.15x voltage)
20 dB above than the noise reading (equals 10x voltage)
7. Record the signal generator output level.
Signal to Noise Ratio (SNR) Page 55
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