[TowerTalk] RE: 6db per s-unit?

[Marijan Miletic]

Ron, KU7Y provides accurate reference for S9 at HF, ie. 50uV.  VHF uses 5uV
only as they live in quieter world and can't generate as much power as we do
on HF but admitedly, they have better and lighter antennas.
Once we calibrate S meter to show S9 on one band with 50uV input, we find a
lot of variations accross 1,8 - 29,7 MHz range and this data is usually shown
in all the equipment reviews.  Detailed reports are in graphic form schetcing
the deviation of real S meter reading from the straight line with 6db per S
unit.  HF RX have over 100dB dynamic range which is less than 120dB of human
ear but we are protected by AGC (automatic gain control) which keeps audio
output at constant level while supplying control voltage to S voltmeter.
Why 6db per S unit?  Matter of convinience of measurement as we simply half
the input antenna voltage and get quarter of power known as 6dB ratio...
How good are the S-meters on modern rig?  Trust them in the range S5 to S9
plus 20dB for comparissons.  They are usually overoptimistic on the low signal
levels and conservative with high levels while trying to prevent smoke :-)
73 de Mario, S56A, N1YU.

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