locked Re: Measuring and matching 10.7 MHz ceramic filters


newaag
 

On Mon, May 4, 2020 at 10:27 PM, Radu Bogdan Dicher wrote:
Bob, David - does this look better? Readings largely OK? More filters data would likely make it more reliable to vet the setup, but this is what I got this far.
It still looks slightly off, but better. What filter are you using? It looks like a defective filter from your displays.

Can you try another 2 or 3 filters, both 280's and 150's? You should have some of those I believe. If no change - calibrate the nanoVNA centered at 10.7 MHz, and save it. Most come with factory cal, but it may not be spot on, or was corrupted...
You can do it on the nanoVNA unit without PC and save it into the last of 5 registers. But restrict the bandwidth first to 800 kHz centered at 10.7 MHz. And do it at the end of the SMA cables. PS - use a chopstick or or stylus to tap the screen if you have big fingers like me. Wait until the selection goes green before releasing. 
The filter should look symmetric on both sides on the bottom. 
You can also cal from nanosaver, and save it there on the PC.
For a decent filter, the group delay should be mostly symmetric on both sides, with mostly equal side saddles. But not every filter is decent. 
Bob
 

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