Does this scope have a real separate 50Ohm input?

I'm surprised at the low noise it has comparing other models....

What exactly do you want to know?

The SDS6000 is still a general purpose MSO with universal BNC inputs that can be switched from high-Z to 50 ohms.

The relevant question would be: what is the input return loss in 50 ohms mode?

The answer is: VSWR < 1.2 up to 1.2 GHz, VSWR < 1.4 up to 2 GHz (typical)

Regarding the noise, there is little difference between high-Z and 50 ohms inputs. Yet the 1 meg inputs are a bit more quiet, which shouldn’t be too much of a surprise because of the nice lowpass filter created by the input capacitance of the high-Z architecture.

According to the datasheet, the SDS6000 is limited to 1 GHz at input gain settings below 2.3 mV/div. Yet the actual gain difference is less than 3 dB at 2.5 GHz, so the noise bandwidth is almost the same. In any case, this is the reason why I provide measurements not only for the highest sensitivity of 500 µV/div, but also for 2.3 mV/div.

Input 1 meg, gain = 2.30 mV/div, BW = 2 GHz: 116 µVrms noise

Input 50 ohms, gain = 2.3 mV/div, BW = 2 GHz: 142 µVrms noise

Input 1 meg, gain = 500 µV/div, BW = 1 GHz: 116 µVrms noise

Input 50 ohms, gain = 500 µV/div, BW = 1 GHz: 128 µVrms noise

See corresponding screenshots

SDS6204_Noise_FFT_1M_2.3mV_2GHz

SDS6204_Noise_FFT_1M_500uV_1GHz

SDS6204_Noise_FFT_50_2.3mV_2GHz

SDS6204_Noise_FFT_50_500uV_1GHz