[R-390] R-390A dB meter as as "S" meter

[DJED1 at aol.com]

<Interesting.  Which manual are you referring to?  As I  mentioned in 
another post, the manual I generally use (NAVSHIPS  0967-063-2010) 
says the carrier level meter should read at least "40" with  10 uV 
from an AN/URM-25( ) connected to the unbalanced input, and "60" +/-  
2 with 100 uV, measured at 15 MHz.>
 
I'm referring to figure 41, p75 of TM 11-856A.  The graph shows a  linear 
plot starting at 20 dB=10 uv, and extending to 100 dB.  If you  extend the 
line through 0 dB, it passes through 1 uv.  Perfectly  reasonable, except my 
radio never followed the curve to within 20 dB, and I  expect they were all 
the same.  Mine was wildly optimistic, and that's what  your NAVSHIPS 
reference says.  So that's why I think the Fig 4 graph  disappeared, never to be 
seen again. But based on the graph I think the  Army would have liked the 
radio to satisfy that scale within some degree of  accuracy. 
Having said that, I'll stand corrected that S9 should be closer to 50  dB.
I've found the SP-600 meter to be pretty accurate at high signal levels,  
given that you're trying to read a scale where 1/16 inch = 20 dB.
Ed