Re: [Discuss-gnuradio] offset at input of LF_RX

[Matt Ettus]

>
> If there is no dc-removing capacitor in the circuitry , then should I
> not expect that for a board using a single (positive) supply, that the
> signal is always above zero?
>


No, you can put a negative voltage in, as long as it doesn't go below
-3.33V.   You need to look at the schematics -- the 8132 is a
differential opamp with a common mode output set at 3.3V/2.

Basically, the differential amps will clip if you go outside the range
of -3.3V to +3.3V.  You will also damage the differential amp if you go
below -3.3V.

The ADC will clip if you go outside the range -2V to +2V when set for
minimum gain.


Back to the subject of  what your signal generator is doing, I don't
know.  If you measure the voltage on the sma connector with nothing
connected, you will see that it is 0.  If you connect a 1 V source
through a 50 ohm resistor, you will see that there is 0.5V at the
connector.  If you connect -1 V through a 50 ohm resistor, you will see
-0.5V at the connector.

Matt