[R-390] Measuring Sensitivity

[Bob Camp]

Hi

The way sensitivity is defined it's the output level that the  
generator *would* put out into 50 ohms that matters. The actual  
voltage into the receiver is never measured. If you have a high input  
impedance radio, it gets to use 2 uV when the generator is set to  
1uV. If you go back far enough generators used to have external pads  
to get the output impedance to 50 ohms to make this all work.

Strange but true ...

Bob
KB8TQ


On Mar 10, 2007, at 2:48 AM, John Kolb wrote:

>
> If the signal generator is outputing 1 microvolt across the 1/2 ohm  
> resistor, the receiver
> will see 1 microvolt at it's input with any reasonable receiver  
> input impedance. The exact
> value of 1/2 ohm in parallel with 50 ohms is very, very close to  
> the value of 1/2 ohm
> in parallel with 700 ohms.
>
> I believe that 50 ohm output signal generators are calibrated so  
> that the output reads
> correctly when the generator is loaded with 50 ohms.  So the  
> receiver would see 1 uV
> at frequencies where it's input was 50 ohm, but almost 2 uV at  
> freqs where it's input impedance
> is 700 ohms.
>
> John
> KK6IL
>
> At 11:38 AM 3/9/2007, you wrote: