Tag Archives: insertion loss repeatability

HPAK 8763B switch test

The 8763B is a very useful device, a 4-port coaxial switch, and has been sold for many years by HP, Agilent, and still sold by Keysight today.
It is single-ended terminated, and has two latching switches.

8763b switch

Two of these will give a nice transfer switch, for auto-calibration (through-connection vs. DUT) of the attenuator test setup.

These switches are specified up to 18 GHz, and have a “max. 0.03 dB insertion loss repeatability”. Now, the big question is, what is the actual repeatability. Knowing the manufacturer, it can be 10 or 100 times better, but you never know. This is fairly critical, because a combined uncertainty of 0.06 dB, for the two 8763B forming the full transfer switch would be not acceptable for the purpose of calibrating attenuators to better than 0.1 dB precision/linearity.

So, quickly hooked this up to the not yet auto-calibrating setup, and recorded power traces, 40 points each, 1 measurement per second, and switching the 8763B in and out every 10 seconds (vertical lines).

This was done at 4, 8, 12, and 18 GHz, and for all ports of the switch.

The setup
8763b test setup
(green item on the right hand side is the feed line directional coupler, connected to the Micro-Tel SG-811 source; light blue test cable on the left is going to the Micro-Tel 1295 receiver).

The results (two examples; same finding at all frequencies) are not very difficult to interpret:

8763b test 1

8763b test 2

– There is not really any switching visible, and one can only judge that the repeatability is actually +-0.002 to +-0.004 – the noise of the measurement.

It seems the only way to get more accuarate data will be to measure the repeatability with the two switches in series, in the final setup. Even though I’m using high quality microwave test cables, 0.002 dB amplitude stability, at 18 GHz is a challenge.
Will need to let the source and receiver fully warm up and stabilize, and use long integration times, like several minutes per switching event, to get data of 0.001-0.002 dB resolution. For now, it seems the switches will add much less uncertainty to the setup as initally thought.