At 07:45 AM 6/13/00 +0100, Ian White, G3SEK wrote:
>According to the lab reviews in the magazines, most modern receivers
>seem to be calibrated so that the difference between S9 and S9+20 is
>pretty close to 20dB. Below S9, the scale looks linear but the dB per S-
>point is not! It typically takes many more dB to get from S2 to S3 than
>it does to get from S8 to S0 - often less than 3dB per S-point at the
>top end.
>
>It doesn't have to be that way - there are engineering solutions that
>could easily deliver the full IARU specification - but when everybody on
>HF is "five nine" anyway, who cares any more?
>
>73 from Ian G3SEK
Ian and all,
I gotta put my two cents worth in for this one and even tie it back to AMPS
type topics.
As has been said before, the manufacturers correctly assume that the
majority of buyers are technical idiots. Have a S-meter that has 1 dB per
S-unit and about 5 uV for S 9 is a good marketing thing. Besides it's a lot
cheaper to build.
I would hope that anyone who actually cares about such things would take
the time to "calibrate" the meter on their store-bought radio. Since I do
this with all my radios, I would not care to pay extra for a manufacture to
make a feeble attempt at a real meter.
Using a HP8648C generator (at 14.1 MHz) this last time, I produced the
following chart for my FT1000D:
S1 = -103.5 dBm
S2 = -101.5 dBm
S3 = -98 dBm
S4 = -94 dBm
S5 = -90 dBm
S6 = -85 dBm
S7 = -80 dBm
S8 = -75 dBm
S9 = -70 dBm
+10 = -60 dBm
+20 = -51 dBm
+30 = -42 dBm
+40 = -33 dBm
+50 = -24 dBm
As you can see, it's kinda poor at the bottom end, but quickly stabilizes
at about 5 dB per S-unit. With S-9 being within 3 dB of 50 microvolts and 5
dB per S-unit, this particular FT1000D has the best S-meter out of the 10
or so radios I've checked.
With a chart like this handy, it gives you a real good idea just how good
the other guys antenna is or how much gain his amp really has. While the
guy on the other end is usually an idiot and won't believe what you tell
him, at least you will know for sure.
Since it's so easy to do this, I'm surprised there aren't more folks with
handy little charts for their radios. I know, not everyone has a room full
of good test equipment. But I bet most people on this list know someone who
does or has access to it one way or another. Give it a whirl, you might be
amazed!
73,
Larry - W7IUV
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