[TowerTalk] Test Fixture for Common Mode Chokes

[Steve Harrison]

On 1/23/2026 11:20 AM, David Gilbert wrote:
>
> Any thoughts on this text fixture?
>
> https://www.youtube.com/watch?v=AyURuo0UEdE

Having designed and built my own S- and Y-parameter test jigs back when 
I worked professionally in the field, I would have two concerns:

1. Those little slide switches likely have very limited lifetime, such 
as only 100 or 200 activations before they might become flaky. Thus, I 
would activate them as sparingly as possible. In fact, I would probly 
seek and stock a set of replacements now, just in case they become flaky 
later.

2. Test jigs such as these (especially at higher frequencies) only 
provide repeatable data when they are always placed in exactly the same 
configuration, each and every time, including the device under 
measurement. Handling and moving the jig, particularly while under 
measurement, is a strict no-no and must be minimized. In fact, I would 
be inclined to mount the jig to the nanoVNA using semirigid coax so that 
at least the relative positions of those two test items is always 
maintained the same every time. However, these precautions are really 
only needed if you wish to be able to repeat prior measurements easily; 
for rough "go/no-go" measurements (especially at lower frequencies), 
such rigidity isn't totally necessary.

Steve, K0XP