[Kenwood] Re: [TS870] S Meter

[Alan Wolke]

Jim,

I made a couple of measurements on my TS-870S tonight to see how the
S-meter reponds.  This was done on 20m, USB (AIP off, i.e. no AIP
indicator), no attenuation.  I used a RF signal generator and a step
attenuator with 1dB resolution.  I started out by adjusting the signal
generator output to give S9 reading with the attenuator set to 0dB.
Then, I recorded the attenuation level required to light-up / turn-off
each segment of the meter.  Here are the results.  The SEG column is the
number of segments illuminated, and dB is the attenuation level, and Sx
is the S-meter level:

SEG    dB    Sx
15        0     S9
14        6
13        9
12       13     S7
11        16
10       18
9         20    S5
8         21
7         23
6         24    S3
5         25
4         26
3         27    S1
2         29
1          31

What you can see from these measurements is that the S-meter is NOT
linear in dB over this range.  It is close to 6dB / S-unit at the S9 end
of the meter, and 1-2dB per S-unit at the S1 end of the scale.  At the
top end of the scale, it is about 4dB/segment.  This holds fairly
constant above S9 also, since there is about 5 segments per 20dB above
S9, and some additional measurements that I made basically confirmed
that the "red" end of the meter is pretty close to being accurate (20dB
change indicated is basically equal to a real 20dB change).  Since there
are 15 red segments from S9 to S9+60dB, this means that it is pretty
close to 4dB per segment in this range.

I hope you find this interesting/helpful.

73,
Alan W2AEW


Jim Balls wrote:

>
>
> Hi all,
>
> Anyone know what the rough DB is for one light on the S meter?
> Trying to do some F/B tests on my beam and it's difficult to know
> without
> some idea of the S Meter calibration
>
> Regards,
>
> Jim M0CKE
>