Some further comments on my post:
- The attenuator method may be required in cases where the output of the NanoVNA is too high for the device being tested and will either damage or overload it. This is the case when testing pre-amplifiers or the input of radio receivers. With NanoVNA's the lowest output possible is about -10 to -13 dBm with 2 ma. of Si5351 drive current which is quite high for many DUT's.
- In this example only CH0 is being used. An antenna would normally not be tested with this method. But I used an antenna for this example only because it shows a wide range of complex impedance (R and X) and SWR.
- If the gain versus frequency of an amplifier is being measured then 2 attenuators may be required. One on CH0 with enough attenuation to not overload the amplifier input and another on the input of CH1 so that the maximum level is kept below 0 dBm. For example if the NanoVNA output is 0 dBm; the amplifier has a gain of 30 dB, and the maximum amplifier input is -20 dBm you would need a 20 db attenuator on CH0 and a 10 dB one on CH1. You would do the SOL, Isolation and Through with both in place.
Roger
Roger Need