Hi Gary I note that you are engaged in this topic so please to
explain to me in a few words how it relates to the subject of dual S11
S21 measurements. Isn' t this just a feature of the dual detector
architecture ,very useful in tuning a filter and such
PS I have virtually dropted out of Ham Radio but will remain
interested in VNA discussions
73 Ron
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On 2021-02-15 12:35,e Gary Johnson wrote:
On Mon, Feb 15, 2021 at 09:12 AM, Brian k wrote:
Has anyone previously implemented (using myVNA) an active loop injection
measurements as described in the above link?
Yes, during development of an audio amplifier.
The VNA output was coupled to the summing node of the differential input stage, with suitable attenuation. The method described by Ridley is effectively the same thing. The key is to maintain normal closed-loop operation especially at low frequencies where loop gain is extremely high. Some math is required to extract the open-loop transfer function. The reference for that is included on a graph on the above webpage.
Gary NA6O
