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Re: Am I in the right track ?
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Putting your hand near the antenna (or, really, anything) will also "load" it with a lossy medium, improving the match.
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As noted before, though, most people do this by using a tool to design it (e.g. HFSS), build it, check the performance in a "radiated field strength" way, and call it done. If you need to verify the design - you simulate the entire thing (fixture, connector, etc.) and then compare. Getting rid of the feedline effects is more art than science. Absorber around the feedline (be it ferrite beads, absorbing tape, or whatever) also is putting absorber in the near field of the antenna. For what it's worth, there's some interesting tape from Laird that is basically a flexible sticky material loaded with ferrite of some kind or another. We use it for emi suppression at work on equipment that's sensitive. -----Original Message-----
From: <[email protected]> Sent: Feb 24, 2025 9:40 AM To: <[email protected]> Subject: Re: [nanovna-users] Am I in the right track ? Yes, you're on the right track. However, I'd strongly recomment you place several appropriate clamp-on ferrites on your feedline right where it exits the assembly. Also place a few at the VNA, itself. As a test, with the assembly laying on your wooden structure, run your hand up and down your feedline between the assembly and the VNA. If you note changes on the VNA while doing so, you require more decoupling - ferrites. And while grabbing the assembly: when grabbed and the VNA traces change, something requires decoupling. Certainly it's an indication your hand and arm are becoming part of the radiating structure - not desirable. A free-space full wavelength at 902 MHz is 13-inches (33-cm). That PCB is nowhere near even a 1/4-wavelength. Therefore, a good portion of a "real antenna" is missing with the assembly. In your first and third photos, I note what appears to be a metalized membrane laying below and to the right of your wooden structure. It has a circle of what appears to be a conductive circle. When the assembly is put completely together, that may serve as part of the radiating structure? And remember, SWR isn't a sole indicator of a good antenna!!!. Rely on the Smith Chart or the complex reflection coefficient, not just SWR. Those two parameters will tell you a WHOLE BUNCH MORE than just SWR. Besides, we're not attempting to protect any final amplifier that "requires" a low SWR to survive. It's such low power that even an infinite SWR likely would not damage anything. Dave - WØLEV Virus-free.www.avg.com On Mon, Feb 24, 2025 at 2:36?AM Nico via groups.io wrote: Once again,-- *Dave - WØLEV* -- Dave - WØLEV |
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