[1000mp] S Meter in MP

Thu, 27 Dec 2001 17:15:33 -0600

I think I will try the same experiment that you did Tom when I get back to
Idaho where the MP is. Here in Minnesota I currently have a TS-870 and by
coincidence had run essentially the same experiment on it as you ran on the
MP.

Interestingly, my results were somewhat like yours in that the meter was
very non-linear below S8 and the S9 level was approximately -73 dBm.

On the low readings remember that this is a test on the bench and the signal
to noise ratio is quite good!

Readings made at 3787 kHz, CW mode, 600 Hz bandwidth, 50 ohm load. WaveTek
3000 Generator

(-137 dBm)0.03   microvolt  = detectable signal
(-133 dBm)0.07   microvolt  = (S7 signal for 160 meter DX !)
(-123 dBm)0.24   microvolt  = quite audible, but no S-meter reading
(-113 dBm)0.70   microvolt  = very audible, but no S-Meter reading
(-109 dBm)0.84   microvolt  = 1 bar on the S-meter (signal loud)
(-102 dBm)= S1   (3 dB to get to S3)
( -99 dBm)= S3   (4 dB to get to S5)
( -95 dBm)= S5   (8 dB to get to S7)
( -87 dBm)= S7   (10 dB to get to S9)
( -77 dBm)= S9
( -61 dBm)= S9+20
( -43 dBm)= S9+40
( -23 dBm)= S9+60

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Tom (xmission)
Sent: Thursday, December 27, 2001 11:52 AM
To: [email protected]
Subject: [1000mp] S Meter in MP

I was interested to read this thread about the S-meter in the MP.  For any
of you who are interested, I thought I would pass along the results of some
testing I did on my MP's S-meter recently.  I have always suspected that my
S-meter is quite generous.  So I brought home a Hewlett Packard HP E4432B
calibrated RF signal generator from work to check it out.

>From what I understand, the traditionally accepted definition of S9 is a 50
microvolt rms signal at the 50 ohm antenna input to the radio.  A little
algebra shows this to be the same as a signal level of -73 dBm.  And for the
size of an S-unit, I used the common 6dB-per-S-unit assumption.  So, in my
calculations, S8 = -79dBm, S7 = -85dBm, 10dB over S9 = -63 dBm, etc.

My goal was to create a simple graph showing the indicated S-meter reading
on one axis, and the correct S-meter reading on the other axis.  I was a
little disappointed to find that there are lots of things that make huge
differences in the indicated versus true S-meter readings.  The curve was
very different for each band I tested (80, 40, 20, 15, 10), and it was
different depending on whether the preamp (menu setting 8-4) was set to
"tuned" or "flat."  So I ended up with a family of curves on my graph.
Fortunately it didn't change much with the IF bandwidth setting, or that
would have made it even worse.

I would also like to thank the author of the nice little program "S-Meter
Lite" which was very helpful in capturing the S-meter readings for each
condition.  For example, I started out with a signal level of -33dBm (40
over S9), and then decreased in 5 dB steps until I got to S9.  Then I kept
going down, but in 6dB steps to hit S8, S7, etc.  The S-Meter Lite program
captured a little graph of the S-meter setting as I let it pause on each
reading for a few seconds.  Then I entered all the data into an Excel
spreadsheet and made some calculations, and finally the graph, from these
recorded values.

Just for a teaser, here's what I got for a power input of -73dBm (which
should have indicated S9 on all bands, I would assume).

Condition                Indicated on MP

80M Flat                 S9+14dB
80M Tuned             S8.2                 (the best--actually quite good
for indicated levels above S9)
40M Flat                 S9+10dB
40 Tuned                 S9+2.5dB
20M Flat                 S9+15dB
20M Tuned             (same as 20M flat)
15M Flat                 S9+12dB
15M Tuned             (same as 15M flat)
10M Flat                 S9+15dB
10M Tuned              S9+26dB       (the worst--WOW, very generous indeed!)

I also found that the slope of the S-meter curves was not too bad for
signals above about S8 or S9.  What I mean by that is that a 5 dB change in
the input signal level produces about the right amount of change on the
S-meter, etc.  In this upper region, the S-meter is just reading too hot by
so-many dB, as the table above hints.  But at about S7 or S8 the indicated
S-meter readings drop like a rock with modest reductions in input power.
Going from indicated S6 to S2 is only about 6 dB change in input signal
level, but it should be 24 dB to cover 4 S-units.  So the bottom half of the
S-meter is pretty useless, if you ask me.

If anyone would like a copy of the jpg image of the graph, I'd be happy to
email it to you ([email protected]).

You know, I was kind of disappointed that the good folks at Yaesu didn't do
a better job on the S-meter in such an expensive radio, and otherwise
fabulous radio.  Obviously the AGC-derived S-meter signal is digitized,
since it can be read via the CAT port by the program S-Meter Lite.  So it
would have been a simple matter to run the digitized S-meter word through a
lookup table and correct it for the various mode settings, so that it
produced a more accurate result.  I don't think it would have cost them a
penny in recurring cost--just a little additional software (OK, maybe a few
bytes of extra ROM) between the segments on the front panel, and the
digitized S-meter value.  But alas...

Does anyone have any different experience?  I only have one radio to
test--mine.  Perhaps yours is different.

Best of 73,
Tom / W7GT

----- Original Message -----
From: "Arie Kleingeld en Marian van Boheemen" <[email protected]>
To: <[email protected]>
Sent: Saturday, December 15, 2001 7:52 AM
Subject: Re: [1000mp] Main versus Sub Receivers

> Byron,
>
> Yes, this makes sense!
> I noticed a small difference is  the s-meter readings also, but only under
> s8 or so.
> The s-meter of  the main receiver is not to be trusted, try listening to
an
> s8 signal and then swith in the attenuator. Ever 6 dB the s-meter should
> drop 1 s-point. Well, it drops, but never one s-point....... try this! My
> s-meter drops at least 2 or 3 s-points. So dont worry about those
s-meters.
> By setting the if gain to 13, the agc kicks in with weaker sigs, so the
> s-meter will come up on those weaker sigs. When the sigs are above s9,
> difference of a few dBs is not noticable on any of the two meters.
>
> About the pre-amp: the flat amp gives more gain on 40 than the tuned amp.
On
> 40 I can swith off the tuned amp (IPO) and see barely any difference
(maybe
> one or two dB, not more). Can anybody tell me why it is there?
>
> Happy new year everybody.
>
> Arie, PA3AAM
>
>
> _______________________________________________
> 1000mp mailing list
> [email protected]
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>

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