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G0HZU_JMR · 8th Mar 2021, 6:59 pm

To test the input 50R termination of the directional filter I'd be tempted to just use a DMM to measure the resistance across the input SMA connector at the internal soldered post (PCB) side of the SMA connector. I wouldn't recommend touching any part of the directional filter itself with the probe tips. Then ground the other end of the DMM to the metal body of the SMA connector. Hopefully it will show 50 ohms. If not then there is almost certainly a broken connection somewhere.

Do you have a 6GHz HP8753D VNA? Looking at your colour plots I guess it is the full 2 port 8753D. This is a very nice full 2 port VNA. It really is worth trying to set yourself up with a fully corrected SMA cal kit if it is a full 2 port 8753D.

This needn't cost much. My first SMA cal kit (for a full 2 port VNA) cost very little because I made it from salvaged SMA connectors but even if you bought new SMA connectors it would only cost about $50 including some test fixture SMA connections that would get used for some PCB dev work.

8th Mar 2021, 6:59 pm	#87
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: Spectrum Analyser TR4172 To test the input 50R termination of the directional filter I'd be tempted to just use a DMM to measure the resistance across the input SMA connector at the internal soldered post (PCB) side of the SMA connector. I wouldn't recommend touching any part of the directional filter itself with the probe tips. Then ground the other end of the DMM to the metal body of the SMA connector. Hopefully it will show 50 ohms. If not then there is almost certainly a broken connection somewhere. Do you have a 6GHz HP8753D VNA? Looking at your colour plots I guess it is the full 2 port 8753D. This is a very nice full 2 port VNA. It really is worth trying to set yourself up with a fully corrected SMA cal kit if it is a full 2 port 8753D. This needn't cost much. My first SMA cal kit (for a full 2 port VNA) cost very little because I made it from salvaged SMA connectors but even if you bought new SMA connectors it would only cost about $50 including some test fixture SMA connections that would get used for some PCB dev work. __________________ Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 8th Mar 2021 at 7:04 pm.