True enough about S-meters historically being a relative indication. There
was a time in late 50's and early 60's when the "S-meter wars" started
between the manufacturers, mostly Hallicrafters and Hammerlund. On each
successive model, they boosted the sensitivity so that if you did a
side-by-side comparison, the radio showing the highest reading would be
thought to be superior. The strategy worked for a while, until everybody got
wise!
I think that was about the time that the S-9 = uV, and 6 dB per S-unit
standard got popular, and Collins stuck to it pretty rigorously. They are
still known as having "Scotch" (as in 'tight-fisted') meters.
Obviously readings are relative since a receiver hooked to a dipole at 10'
will read far less than one connected to a 6 over 6 over 6 array on a 180'
tower. The benefit of accurately calibrated meters are to help in antenna
comparisons, getting a "ball-park" on F/B ratios, relative conditions
between stations that talk on a regular basis (I do that on 75 all the
time), comparing two stations in nearby locations, etc. Both my KWM-380 and
my TS-870 have S-meters that are remarkably accurate, although I determined
that the '380 uses a 5-dB/S-unit standard instead of 6. The 870 has a
menu-selectable option that automatically changes the S-meter reading to
compensate for the preamp.
It would be nice to have readings that correlate to a known standard in the
Orion.
Ron
N6AHA
----- Original Message -----
From: "Lin Davis" <linbdavis@earthlink.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Saturday, February 18, 2006 11:16 AM
Subject: Re: [TenTec] Orion (original) S-meter
Just a note about S-Meters. From what I've read it was only
ever intended as a relative signal strength indication,
meaning that from one receiver type to the next, there is no
correlation. It looks like rig vendors are at least starting
to calibrate them at one point, S9/50uV. Traditionally, the
actual measurement was of the AGC voltage. How this voltage
tracks signal input level is completely dependent on the
gain control characteristics of the rf/if amplifiers
involved, so it is highly variable. So I don't believe it
makes sense to say that +10 over S9 means 10dB over S9, etc.
But now that we have software running our s-meters, it is
possible to display a calibrated signal level measurement,
taking preamps and attenuation into account, with the scale
in dBm or dBuV, rather than S units. Unfortunately, I don't
think this would be an easy thing for manufactures to
do. Each rig would need to be calibrated independently,
given the component variations from unit to unit.
... ramblings from this engineer :)
73,
Lin
WB1AIW
-----------------------------------------------------------
Ron Castro wrote:
> Whoops...I didn't mean for it to come out like that! Lets try this...
>
Reformatted:
Orion II S-Meter Readings from Ron Castro, N6AHA
from E-mail rcvd February 18, 2006
Standard Standard Orion II Pre off Orion II Pre on
S-Units uV dBm pre off Descrep Pre on Descrep
S-5 3.16 -97 S-2 -12 dB S-6 6 dB
S-7 12.57 -85 S-5 -12 dB S-9 12 dB
S-9 50 -73 +5 5 dB +30 30 dB
+10 158 -63 +25 15 dB +42 32 dB
+20 500 -53 +40 20 dB +55 35 dB
+30 1583 -43 +52 22 dB +60 30 dB
+40 5006 -33 +62 22 dB Off Scale N/A
+50 15830 -23 Off Scale N/A Off Scale N/A
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