[sdiy] Equation for converting V PP to dBm?

[Andre Majorel]

On 2011-12-31 13:33 +0000, Tom Wiltshire wrote:
> On 31 Dec 2011, at 13:04, Justin Owen wrote:
> 
> > ...and this: http://www.sdiy.org/juz/2164_comp_CV_DB_01.jpg
> > - which shows CV against DB.
> > 
> > Interestingly, as Andre mentioned - my measurements start to
> > fall off below approx. -40dB / 0.05 V PP - but I'm pretty
> > sure I can work on that.
> 
> I had a discussion with George Hearn about this at SDIY UK
> 2010. He'd been studying the SSM2164, and noted that the VCA
> drops off sharply to zero at the far end. He didn't consider
> it a problem since it closes the VCA completely, which is
> probably what you want. Although I don't remember him saying
> that he'd see the effect from -40dB onwards, more like -80dB.
> 
> But he had spotted the same pattern, so you're seeing a chip
> characteristic, not a measurement effect, I reckon.

If Justin's DMM had the same error as mine, he'd see the
opposite effect : curve asymptotically approaching -60 dB.

-- 
André Majorel http://www.teaser.fr/~amajorel/