There are quite a few coaxial switches around – I figured that I need two transfer switches to accomplish the task of “through” calibration, and reflection/insertion loss measurement.
Any unused ports should be automatically terminated with 50 Ohms, when switched out.
Looking around, I found that the HP/Agilent/Keysight (will call it HPAK from now on, and add further letters, with next name change of this wonderful company) HPAK 8763B transfer switch, offers really good data, especially on repeatability. 0.03 dB – for millions of cycles.
Determining this switching reproducibility will be the first task for the attenuation calibrator!
They go for USD 813 each (August 2014), but you can find them much cheaper elsewhere. Preferably, get a unit that doesn’t have 10 million+ cycles yet!
These are of latching type – so we will have to device some drive circuitry to switch them, 24 V positive supply. Won’t be too difficult.
Interconnections will all be rigid coax, and precision SMA to N test cables to connect to source/receiver.
Note the Sage 0.5-18 GHz coupler, left of the switches. This will be used to get a sample of the SG-811 signal – stay tuned.
For this coupler – this item was found on xbay, quite reasonably prices for its bandwidth. However, the coupled port has a little damage of the SMA connector – rendering it non-usable for its original destiny, but will now be very handy for this project.
To the outside world, the interface is a pair of HPAK SMA (3.5 mm) to precision N panelmount transitions. These are the best and most reliable know to me to date.