[amsat-bb] Re: receiver sensitivity conversion question

Grant Hodgson grant at ghengineering.co.uk
Thu Mar 22 01:33:12 PST 2007


Usually, an RF voltage is specified as potential difference (PD), i.e. 
the voltage when connected to a 50 ohm load.

To convert uV to dBm :-

i) work out the power in Watts :-  P=V^2/R so 25uV equates to 12.5pW or 

ii) Multiply by 1000 to give the answer in mW; i.e. 0.0000000125mW.

iii) Take the logarithm and multiply by 10 to give -79dBm.

However, I'm not sure where 12.5uV comes from - a typical VHF receiver 
needs about 0.25uV or better - that's -119dBm; if your radio really 
needs 25uV then there is something seriously wrong.


Grant  G8UBN

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