Inheriting from ZNB to support other R&S VNAs

[abargerbos]

Hello! In

Qcodes/src/qcodes/instrument_drivers/rohde_schwarz/ZNB.py

Line 1057 in d4e1e15

m_frequency = {

, would it be possible to move

m_frequency = {
"ZNB4": (9e3, 4.5e9),
"ZNB8": (9e3, 8.5e9),
"ZNB20": (100e3, 20e9),
"ZNB40": (10e6, 40e9),
}

outside of the init so that it becomes a class attribute that we can override, and then in the init just do

if model not in self.m_frequency.keys():
raise RuntimeError(f"Unsupported ZNB model {model}")

The same question would hold for

        self._model_min_source_power = {
            "ZNB4": -80,
            "ZNB8": -80,
            "ZNB20": -60,
            "ZNB40": -60,
        }

in https://github.com/microsoft/Qcodes/blob/d4e1e15de07c4d3a4cd94445dd614637d96aec31/src/qcodes/instrument_drivers/rohde_schwarz/ZNB.py#L440C1-L445C10

If this were the case, we could inherit from these classes and add support (in our local codebase, not asking you to support them explicitly!) for other R&S VNA's, such as the ZNL and the ZNLE. These VNA's follow the exact same programming as the ZNB but have different ranges for their frequencies and powers, for which right now we have to copy & paste most of the ZNB driver and adjust these few lines.

[jenshnielsen]

@abargerbos That sounds file, please feel free to make the changes and submit a pr.