"Serge Auckland" wrote in message
...


"Keith G" wrote


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


Probably not, asitappens:

http://en.wikipedia.org/wiki/Atto-



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


OK, disregarding the 'SI prefix' confusion, there's summat not too clear
here but the tuner's been retired pro temps in favour of the....

.....wait for it....

....DAB tuner...!!

As Swim picked it consistently over the FM tuner last night (or the the
night before) as she thought the FM was comparatively boomy and that
there was a feint hiss with a signal strength of about 55 dBf, so your
figure of '80 dBf' for *completely* clean audio might not be too wide of
the mark?

(No good asking me - the FM sounds as 'good as CD' to me!! :-)