Hermes as a VNA: Transmission

Tonight I found a short time to try out the VK6APH VNA code to use my Hermes Board/ANAN  10 as a VNA.  

As suggested in the V1.9 user manual I put a 6dB attenuator on the Hermes TX output to define the source impedance for measurements as 50 ohms

First I connected the TX output through the 6dB attenuator to the RX input and carried out the calibration routine. Just to check it had worked alright, i left the connection in place and hit the measure button, which resulted in the following result

Which is what I expected to see

Next I needed a filter to measure. The first filter that I found was my LF lowpass filter that I used in front of the SDRIQ to keep high power MW stations out of the front end while listening to 136 and 500kHz. This was connected between the TX and RX ports of Hermes still with the 6dB attenuator in circuit. The result is as follows:-

When I can find the necessary adaptor cables, the next task is to use a reflection bridge to measure return loss