On Thu, 28 Apr 2005 00:40:11 -0700, Richard Clark
wrote:

On Thu, 28 Apr 2005 00:11:44 -0700, Roy Lewallen
wrote:

Think I'm likely to find "S-Unit" if I look hard enough?

Yep.



Hi Roy,

One could see stars in the middle of the day if they squint their eyes
hard enough. Seems to me Collins literature covered S Units
adequately and they were certainly the Cadillac of the pro's.
Hammerlund is another probable source. National another. RCA as
early as 1941.

On the other hand, I certainly wouldn't waste my eyes scanning the
shelves of the engineering library.

Scanning my library I spy:

"Fundamentals of Single Side Band", 2nd Edition, Sept 1959, Collins
Radio Company, Cedar Rapids, Iowa.

On page 13-7, in describing the circuitry of the 75S-1 it says in
part:

"The S-meter is calibrated in S-units and dB. The S-unit scale is
standard up to midscale (S-9). The db scale reads relative signal
strength above the avc threshold which is approximately 1 microvolt.
Thus 40 dB on the meter is 100 microvolts of signal (which also
corresponds to S-9 on the S-unit scale). To read dB over S-9 on the
S-unit scale, subtract 40 from the corresponding dB reading. For
instance, a 60-dB reading would be 20 dB over S-9 (100 uv) or 10,000
uv of signal at the antenna. This reading is then 60 dB over the dB
scale reference of one microvolt and 20 dB over the S-9 reference of
100 uv"

Whew.

Next to it I find:

"Amateur Single Sideband", 1st Edition, 1962, Collins Radio Company,
Cedar Rapids, Iowa.

Its only reference to S-meters is on page 111 where, in a section on
distortion tests with a receiver, it states in part:

"Variations and nonlinearities in S-meter calibration can introduce
considerable error in the measurement of signal levels by means of a
receiver. The commonly used figure of 6 dB per S-unit is appreciably
higher than the actual response of many amateur receivers. The meter
in the S-Line receivers, for instance, is calibrated to read
approximately S-9 with and input signal of 100 microvolts. The agc
threshold is set nominally to 1.5 microvolts, and varies slightly from
band to band. Therefore, the total range from S-zero to S-9 under
normal conditions can represent 30 to 40 dB or from approximately 3.3
to slightly over 4 dB per S-unit."