[sdiy] Equation for converting V PP to dBm?

[Neil Johnson]

Hi Justin,

> That's interesting. When I said "I can work on that" - I was  
> referring to being able to get better quality measurements at below  
> -40dB. For the 'actual' 2164 measurements I used the multimeter on  
> my scope rather than a dedicated AC multimeter because it's  
> convenient and it gives V PP - but below about 0.5 V PP - it's not  
> hugely accurate.

You'd probably get better results taking readings from the scope  
screen.  Assuming the vertical (Y) amplifiers can go to 5mV/div you  
should be able to measure with a reasonable degree of precision down  
to around 1mV or so (assuming your scope's Y-amps are reasonably in cal)

> Using a multimeter will mean I'm working in RMS - but I think I can  
> deal with that now.

Only if you have a true RMS reading multimeter, like a decent Fluke  
or Agilent.  Your typical DMM is average-reading.

> Still - using the 2164 as a benchmark and knowing that it  
> potentially has a sharp drop-off below -80dB makes me happier about  
> using a CV of 0 to  2.5V which should get me down to about -75dB,  
> which, for now - is fine (and very convenient)... I think.

To get down to a reliable -100dB attenuation is not trivial.  You're  
down to a few microvolts floating around here and there.

Cheers,
Neil
--
http://www.njohnson.co.uk