[criageek]

Shielded cables in  this particular case do not have to be of particular impedance.
Impedance only matters when your transmission length becomes comparable or especially when it exceeds the wavelength at which point it is considered a resistor equal to the characteristic impedance as seen by the source; otherwise your cable acts as lumped capacitance/inductance as seen by the source, and your shield is there exactly for that - to provide shielding.

Thanks morzh!  I decided this was probably the case and bought some of this from Digi-Key:  https://www.digikey.com/product-detail/e...ND/5270188

Rich