[R-390] Y. Receiver Sensitivity Test

[Flowertime01 at wmconnect.com]

Y. Receiver Sensitivity Test

There may be an occasion when its appropriate to measure and record 
receiver sensitivity in real terms using an accepted standard. For radio receivers, 
real term sensitivity is expressed as the value of a modulated RF voltage 
applied to the antenna input necessary to provide a 10db S/N + N figure. This 
means, what input voltage is required to raise audio output 10 db over the 
receiver noise floor. Some prefer to do the test with a band width of 2 Khz. 
Others prefer to do the test at 4 or 8 Khz. If you are comparing the R390 
to another receiver you would like to use the same band width. At 2 Khz you 
expect the receiver to have a 20db S/N + N figure. This test is preferred as 
a minimum signal test. How small of a signal on the antenna can still be 
copied? An alternative test is, for a fixed signal level, how far is it above 
the noise floor. We see this in the If deck where we expect 150 micro volts 
to provide 30 DB of signal above the noise floor. In the RF deck or end to 
end test we expect 3 micro volts to provide 20 DB of signal above the noise 
floor. Measuring the receiver sensitivity in the R390A is an easy, straight 
forward procedure. The receiver Line Level meter can even be used to help with 
the measurement.

Here is the procedure for sensitivity:

___ 01 Turn the receiver and allow it to warm up for 1 hour
___ 02 Turn the signal generator and allow it to warm up for 1 hour
___ 03 Set the receiver and generator to the same frequency of choice
___ 04 Adjust the Kilocycle Change to peak the generator in the band pass
___ 05 Set the initial generator output to 1uv
___ 06 Set the initial generator modulation level to 400 Hz or 1kc at 30%
___ 07 Set the R390 or R390A Function switch to "MGC
___ 08 Set the R390 or R390A Bandwidth to 4kc
___ 09 Set the R390 or R390A RF gain full CW (Clock Wise)
___ 10 Set the R390 or R390A AF line gain full CW
___ 11 Set the R390 or R390A AF local gain full CW
___ 12 Set the R390 or R390A BFO off
___ 13 Disconnect the signal generator from the receiver
___ 14 Set the Line Meter range switch to -10
___ 15 Adjust the Line Gain for a -10db indication on the Line Level meter
___ 16 Use the Ant Trim to peak the receiver noise alone
___ 16 Readjust the Line Gain for a -10db on the Line Level meter
___ 17 This is the relative receiver noise floor level
___ 18 Connect the generator to the receiver's balanced antenna input
___ 19 Reduce the RF output level of the generator.
___ 20 For a R390 Line Level meter value of 0
___ 21 Record the frequency and the output of the generator in micro volts
___ 22 This value is the 10db S/N + N receiver sensitivity at this frequency
___ 23 It should be less than .5uv 
___ 24 The official specifications of the receiver call for 3 micro volts
___ 25 Work alone the range of the VFO and conduct this test at each MHz
___ 26 .900, 1,900, 2,800, 3,700, 4,600, 5,500, 6,400, 7,300 
___ 27 8,200, 9,100, 10,000
___ 28 To get a value for each Mhz crystal and the range of the VFO.
___ 29 Check the SN + N at the alignment points
___ 30 550, 950, 1,100, 1,250, 1,900, 2,200, 3,800, 4,400,
___ 31 7,250, 7,600, 8,800, 15,200, 17,600 30,400
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