[TowerTalk] Test Fixture for Common Mode Chokes

[Gary Johnson]

The N2PK is fully capable of 12-term calibration and many owners like me built S-parameter test sets. It can be used with the DG8SAQ application that also supports the VNWA, with all its sophisticated processing capabilities. BTW, within its frequency range of 60 MHz, the N2PK has a fairly astounding dynamic range, in excess of 120 dB.

For routine choke measurements, I use my VNWA and do a 12-term cal to the end of my test cables, then add very short (1 inch) SMA clip leads that connect to the DUT in S21 configuration. Up to 50 MHz it’s completely adequate and verifies well with resistors to 10k or higher. The VNWA holds calibration with the fixed test cables very well; I leave it powered all the time. This setup is really handy and easy to use. 

Gary Johnson NA6O  
gwj at me.com

> On Jan 23, 2026, at 6:19 PM, towertalk-request at contesting.com wrote:
> 
> AC0C said:
> 
> "Brian, would you consider the N2PK VNA in the "fancy" category rearding
> your calibration comment?"
> 
> Jeff, I don't think the N2PK measures all four S-Parameters nor does it
> do a 12-term calibration. I was thinking of the HP 8753C and 8753D,
> which are sophisticated VNAs that a surprising number of hams have.