[Racal] RA6790 AGC voltages

[Robert Nickels]

After fixing the most recent problem with my RA6790 (a bad MC1496 in 
A3), I did something I found myself wishing I'd done in the past, and 
recorded some typical AGC voltages.  Fig. 5.2 in the manual shows 
typical signal levels with a very strong (-20 dBm) input signal,  but it 
is useful to know how the AGC system performs all the way down to the 
base sensitivity level when troubleshooting receiver problems.

The following measurements were taken at P1 on the A3 module, in AGC - 
SHORT mode.   Pins 2-4 are the input AGC level from A4 and Pin 6 is the 
amplified AGC signal that is supplied to A2:

Antenna Input     Pin 2-4   Pin 6
1 uV                    12.8        12.4
10 uV                  12.8        12.4
25 uV                   9.9         12.1
50 uV                   9.3         12.1
100 uV                 8.7         12.0
250 uV                 7.8         11.9
500 uV                 7.0         11.9
1 mV                    6.2          11.8
10 mV                  3.2          10.1
25 mV                  1.9          8.6

Rotation of IF GAIN pot In MAN mode:
Full CCW (min)   0.66       12.9
Full CW (max)      6.4        12.4

Since a correctly operating AGC system is critical to the performance of 
the 6790, I thought it might be helpful to others to have these 
measurements for reference.

73, Bob W9RAN