Date: Fri, 23 Jul 1999 01:29:27 -0400
From: "Dave Sergeant" <sergeantd@compuserve.com>
Subject: LF: S-meters and DCF39
To: "rsgb_lf_group" <rsgb_lf_group@blacksheep.org>
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>From Dave G3YMC

I have calibrated my receive set up against a quality signal generator,
calibrated in dBm into 50 ohms.  I won't bore you with the actual figures,
but they show that the use of S meter figures is totally meaningless.  The
s-meter for my FT101ZD is designed to measure the signal at its own
receiver input - this is meaningless when there is a receive converter at
the front end with its own gain, which in my case is appreciable.  I also
do not know the input impedance of my receiver - the figures are for a
nominal 50ohms but would be double for an infinite input impedance.

The important figures are:

DCF39 (875km)     14uV into 50 ohms (-94dBm)
Noise level (typical) 0.1uV into 50 ohms (-126dBm)

S9   0.45uV  (burst of laughter)
1 S point is typically around 2dB, although surprisingly S9 to S9+10
measures as 10dB.

point taken, S meters are meaningless.

Unlike some I get very little variation in the strength of DCF39 - it is
always S9+18 on my meter with a variation of no more than 1dB or so.  I
never ever see the 20 to 30 dB variations some mention.  Reception is
normally on my transmit loop.

Thanks to Geri DK8KW for his dB conversion chart.  However I would request
that he changes the colours on his page.  White text on a black background
looks fine on a monitor, but most of us would like to print it out.  I had
to edit the page before printing so that I could see the white ink on my
white paper....

73s Dave G3YMC
sergeantd@compuserve.com