Neil Smith G4DBN
If the noise blanker is enabled in SW2, or if the bandwidths in SW2 and on the DUO are not exactly the same, you will see differences. Also the time constant on the DUO is long, but short on SW2, so getting a steady reading on noise is hard. Much easier on a solid tone of course. The calibration is within a dB or so of my HP signal generator all the way through the range on single tones. Superhet S meters measure AGC voltage rather than the actual signal power, and things get very tricky with roofing filter IFs being in the AGC loop.
Can't say I ever use S meter readings though, they are pretty meaningless. Signal to noise ratio or relative signal levels are much more useful. The advanced marker measurement is very useful for that.
If Rob Sherwood says it is "close to perfect", that is pretty much case closed.
Check the bandwidths and frequecies are identical and that notches and noise reduction and noise blankers are off. Check if the readings are different on a very strong pure tone and on band noise and a STANAG signal that is fairly constant level and see if there is anywhere the readings do match up.
On 18/03/2020 23:15, Chris Moore wrote:
-- Neil http://g4dbn.uk