On Sun, Feb 11, 2024, 4:29?AM John Zbrozek <jdzbrozek@...> wrote:
Matt,
The input impedance of a VNA is 50 ohms.
The input impedance of a Tayloe detector is quite complicated: very high at the clock frequency, falling away to very low at frequencies far removed from the clock frequency.?
In QDX, signals are received at 12 KHz from the clock frequency, so the input impedance presented by the Tayloe circuit is somewhere between the extremes.
I expect that the difference in filter terminating conditions is contributing to your observations. Also, when you ran the internal sweeps, did you have a 50 ohm dummy load at the antenna port?
I am a bit disappointed that nobody picked up on the results from my previous post... what do people think about this? Are the differences between the two measurements normal? If so, what are they attributed to? It kind of looks like the internal RF sweep feature shows extra loss below the passband that is missing from the external measurement...
