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
[email protected]
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