Re: [amsat-bb] DB'S per s-units on 847

["Edward R. Cole" <al7eb@xxxxxxxxxxxxx>]

>From: "Luc Leblanc (VE2DWE)" <luclebla@sorel-tracy.qc.ca>
>Anyone knows how many DB'S per S-UNITS the 847 meter has been factory
calibrated under S9 mark?
>
>Thank's
>
>Luc Leblanc VE2DWE (AMSAT 33583)

Luc,

Back in June I asked myself the same question and so calibrated my FT-847
with an IFR-500 service monitor thru a 23 dB attenuator from S-1 to S-9:

FT-847 state: internal preamp-ON, DSP-OFF, USB-mode, AGC-slow
-153.0 dBm produced a trace on AO40.RCV and I consider the MDS*
-114.5 S-1
-113.0 S-2
-111.0 S-3
-109.0 S-3.5
-108.0 S-4
-107.0 S-4.5
-103.0 S-5
-101.0 S-6
-98.0  S-7
-88.0 S-9

As you can see it is a very inconsistent and non-linear curve.  I plan to
repeat this for both internal preamp-ON/OFF.  Also I can take the radio to
work and repeat this using an IFR-120 which has better resolution of output
signal [0.1 dB vs. 0.5 dB].  I could also compare this with an external
step attenuator, but they have only 1 dB steps.  {but in truth it is hard
to resolve less than a half s-unit on the FT-847 s-meter}

I generalize and say that the meter runs about 3dB/s-unit.  Obviously that
is a gross oversimplification.  

*From memory, the internal preamp adds approx. 15 to 20 dB gain, so MDS
without the preamp on is loosly about -133 dBm {Yaesu claims sensitivity
-122 dBm}.  In fact my ears need another ten dB so I guess they agree with
Yaesu {but probably means personally I need an S/N of 10 dB to hear a signal}.

Not a lab quality test, but that's what I found.
Ed

Ed

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