[sdiy] Equation for converting V PP to dBm?

[Veronica Merryfield]

On 2011-12-29, at 9:01 AM, Justin Owen wrote:

> Hello,
> 
> I've been researching how to convert a Peak to Peak Voltage into dB and I've come up with 4 slightly different equations which all give different answers. I've also had a few different people tell me that different ones were the 'right' one - so I thought I'd ask here.
> 
> 1) dB = 20*log_10(Vpp/0.707)
> 2) dB = 20*LOG10(Volts_peak_to_peak/SQRT(0.008*Z))
> 3) db = (20log10) (RMS ) & RMS= 0.707*P-P
> 4) dB = 20 log10 (Vout / Vin)
> 
> Recognise any of them?
> 
> What I'm trying to do is plot the response curve of the 2164 based on the data sheet spec of -33mV/dB. I figure if I can convert V PP to dB I'll also have mV to V PP.

It is more usually to quote dBu, referenced to 0.775 Vrms, for voltages in audio work.