PA100-D Input SWR

[KV4TT]

Hello Group,

I am really liking my PA100-D built about 1 year ago. I recently updated the firmware and like it even better now.

One situation I have had since I completed construction is the input SWR is 2 or more on all bands into a good dummy load, when using the G4 attenuator position.

I am interested to find what other builders have found the Input SWR to be, and hear any suggestions for troubleshooting or adjustments if the SWR of my build seems high.

Thank you for any input

73 - KV4TT - Mike

[5B4AIY]

Hi, Mike,
I am posting some swept SWR plots I took of my amplifier. It is perfectly normal for the SWR to be higher when the gain is set to G4. Bear in mind that the presence of an input attenuator will mask SWR problems, and indeed is a common microwave technique for 'improving' the SWR. Provided the driving source can tolerate the increased SWR there is no problem. The increase in the SWR is because the input impedance of the transistors is non-linear.
73, Adrian, 5B4AIY

[KV4TT]

Hi again Adrian,

I just tested each band again and I find that my results are comparing well to your sweeps at each of the 4 attenuator settings

This gives me peace of mind that my hardware is in specification.

I am currently driving the PA100-D with my Elad FDM-DUO, it seems fine with the 1:2 SWR.

Thank you again for your great help!

73 de KV4TT - Mike