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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>
>
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