Perhaps a silly question from a retired doctor.......

On the output port, according to Gabriel’s circuit diagram on the bottom left hand corner, is a pi attenuator with 75ohm parralell resistors and 120ohm series.

This gives 14db attenuation of the output signal. I appreciate that its main function is to stabilise the output impedance seen by the DUT.

However I am more intersted in dynamic range rather than small imbalances to the connected devices. Would a reduction to 4db attenuation give a 10db increase of dynamic range? If I needed greater stablity of output impedance, an addition of an external 10 db attenuator would restore the original specification.

Steve L. G7PSZ

Perhaps a silly question from a retired doctor.......

On the output port, according to Gabriel’s circuit diagram on the bottom left hand corner, is a pi attenuator with 75ohm parralell resistors and 120ohm series.

This gives 14db attenuation of the output signal. I appreciate that its main function is to stabilise the output impedance seen by the DUT.

However I am more intersted in dynamic range rather than small imbalances to the connected devices. Would a reduction to 4db attenuation give a 10db increase of dynamic range? If I needed greater stablity of output impedance, an addition of an external 10 db attenuator would restore the original specification.

Steve L. G7PSZ

Yes you can reduce the attenuation to improve the dynamic range, but the
receiver might saturate with a thru cable connected so you may need to
calibrate THRU with an external attenuator connected.

On 12/08/2020 18:00, Stephen Laurence wrote:

> Perhaps a silly question from a retired doctor.......
>
> On the output port, according to Gabriel’s circuit diagram on the bottom left hand corner, is a pi attenuator with 75ohm parralell resistors and 120ohm series.
>
> This gives 14db attenuation of the output signal. I appreciate that its main function is to stabilise the output impedance seen by the DUT.
>
> However I am more intersted in dynamic range rather than small imbalances to the connected devices. Would a reduction to 4db attenuation give a 10db increase of dynamic range? If I needed greater stablity of output impedance, an addition of an external 10 db attenuator would restore the original specification.
>
> Steve L. G7PSZ
>
>
>

Thankyou.

So if I did change the input resistors to give 4db rather than 14db attenuation, I woud need a 10 db external attenuator to attach when required.

I was just about to add to my previous question by asking if a broadband low noise preamp of 10 or 20db in front of the receiver port would also improve dynamic range, but you have effectively answered my question. A preamp would also add a significant physical path/ time delay and presumably a 180 degree phase shift, both of which I suppose could be calibrated out.

The 4 inch screen version would however possibly have enough empty space to put it somewhere.

On a related subject, what is the input 1db (or .5db or .1db, depending on ones personal threshold) compression point of the v2 input? ( sorry if I have overlooked it in the wiki specs)?

Steve L