Your picture tells a lot.? My guess is that the cans on the same side of the duplexer are over coupled because of improper coax length between the cans. In other words, with the proper 1/4 wavelength , a short on one end creates very high impedance on the other end which gives the most isolation or decoupling between cans on the same side of the duplexer. It may only be off less than 1 inch length at UHF.
Since the best return loss perfectly aligns with least insertion loss, the length of coax between the antenna T and the opposite side cans is the proper length, so that is good.
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John
On 04/26/2025 6:51 AM EDT Part 15 Engineer via groups.io <kc8gpd@...> wrote:
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Ok, I'm tuning the pd526 on the nvna. I can't seek to get everything to line up on both reject and pass simultaneously. It seems to be one or the other. I have attached pic of my latest plot. This is the best I got it so far. I did tune cavities individually then hook them together. And I got multiple peaks and valleys on the plot instead on one nice peak on the pass and valley on the reject. Does anyone have a link to the plot for the pd526 and what it should look?like?
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Thanks
I think I finally got the pd526 tuned. It has 1db difference in sensitivity between direct input and going through duplexer and very little tx power loss coming out of duplexer. Probably only a few watts of loss. Tomorrow I will do some field testing to see if it gets put as far as the txrx 28-70-15h duplexer I was using. I'm not seeing any signs of desense yet.
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It will have the opposite effect.? To get more dynamic range you would really need an amplifier or a way to drive in more signal.? The pads are just to match the impedance as the output/input terminals may not be the nominal 50 ohms.? That is just for the notches.? If tuning the pass with a RLB do not use a pad as this will give a false match/very low RL .
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Ralph ku4pt
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On Thursday, April 24, 2025 at 11:28:09 AM EDT, Part 15 Engineer via <kc8gpd=
[email protected]> wrote:
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Will a pad give the nanovna more of a dynamic range to see? the notch depth? Iirc the dynamic range of a standard nvna is about 60 to 80db. So if I put a 10 or 15db pad that should help with tuning the notches?
Pads can be helpful on the generate side of a VNA providing a good resistive match to the device under test. Many years ago working at Hughes Aircraft we always terminated our generate cables with a 6dB pad.?
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