This - get some 4 leg SMA jacks and solder two of the legs to the copper clad at the edge of the board. Cut the upper two legs off. That will give you a nice transition.
Depending on where you are, you can probably get jacks mail order in a day.
10 of them for $8
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-----Original Message-----
From: <
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Sent: Mar 12, 2025 11:54 PM
To: <
[email protected]>
Subject: Re: [nanovna-users] Help with LPF Measurement
Mitch,
Try making the ground connection to your filter very short, say 5mm or so. Also, try multiple ground wires. The currents to ground from all the capacitors in the filter flow through that ground connection, and if it has much inductance it will have a voltage drop that limits the rejection of the filter.
If you have the connectors available, a better connection method is to solder an SMA connector shell directly to your ground plane at the input and another directly to the ground plane at the filter output. Then connect the center pins of the connectors to the input and output and connect your cables.
If you just have some SMA pigtails (or can make a couple by cutting an SMA cable in half), you can connect the shield of a pigtail to your ground and the center wire to your input and similarly connect an output pigtail. Then connect those pigtail connectors to the NanoVNA.
As others have mentioned, making all the component leads as short as you can will help, but the grounding is probably the bigger factor at this point.
--John Gord
