On Wed, Apr 23, 2025 at 06:31 PM, Clyde Spencer wrote:
This can be improved by adding a small Common Mode Choke at the VNA end to
help isolate the coax from the case of the device.
Clyde, in HTs used for their purpose, which is portable communications, the body of the HT, and even the body of the operator are all part of the antenna. If you mount a rubber duckie directly on a NanoVNA, possibly on a metal bracket, and hold it in your hand, you emulate this situation, and get values close to the real thing. But if you isolate the rubber duckie from the instrument by means of a common mode choke, you will create a very different situation, and totally mess up the measurement!
A rubber duckie at the end of a coax cable will behave totally different than when mounted on an HT.
Manfred
