"Keith G" wrote in message
...

"Serge Auckland" wrote in message
news


"Keith G" wrote

http://www.apah69.dsl.pipex.com/show/Signal.JPG


Is reckoned to be 'good' (or 'good enough')...???

(Certainly sounds OK!!)
Keith:-

If I haven't pressed any wrong tits on my calculator,

55dBf means 55dB above 1 femtowatt, or 10^12 watts
55dB is a power ratio of 3.16 x 10^5
so 55dBf is a power level of 0.316 microwatts.

Assuming a standard 75 ohm antenna, that translates to 4.87 mV, so I'd
say that was a pretty good signal.


Hi Serge - I found this in the manual a little earlier:

http://www.apah69.dsl.pipex.com/show/Voltages.JPG

(RTFM was never my strong suit!! ;-)

How does it sit with your figuring? There's a bit of a discrepancy - is it
easily explained?

(Just out of interest and FYI only - no bother whatsoever to me! :-)


No, not easily explained.
Take the example of 50dBf = 86.5uV 75 ohm
86.5 uV into 75 ohms is a power level of 99.76 femtowatts, call it 100
femtowatts.
That would be 20dBf in my book *if* dBf means dBs relative to 1 femtowatt.

1 femtowatt is 10^-12 AFAIAC

Consequently, their dBf is not relative to 1 femtowatt, or their femtowatt
is not mine.

According to their figures, you would need a signal strength of better than
80 to get completely (audibly) noise-free audio.

Working back, 86.5uV /75 ohm is 50dB relative to 1 attowatt or 10^-15 watt

S.

--
http://audiopages.googlepages.com