There is a filter spurious on the high side of the skirt. This shows up as a spike on the VNA display. There is none on the low side skirt, despite what appears to be a spurious on the VNA display. I put together a 4 pole 77 MHz crystal filter and its swept response on the nanoVNA as well on another analyzer are in excellent agreement. This filter has a reasonable transition BW compared to its center frequency; 1800 Hz at 77 MHz. At this point I would say there is no issue. I will capture its response and post. Alan
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From:
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Sent: Thursday, July 11, 2019 6:19 PM
To:
[email protected]Subject: Re: [nanovna-users] Narrow band filters and LO phase noise/jitter?
This 500 Hz bandwidth filter is problematic. Upon further measurements with another instrument there are issues.
I will find another baseline network and report findings again.
Alan
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From:
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Sent: Thursday, July 11, 2019 4:09 PM
To:
[email protected]Subject: Re: [nanovna-users] Narrow band filters and LO phase noise/jitter?
In crystal factories crystals are measured in a 50Ohm system with a pi-network on both sides as per enclosed picture.
Don't know if the resistance values are readable in the compressed picture so here the are:
Input R1=159 ohms to ground, R2=66,2 ohms in series and R3=14,2 ohms to ground. On the outputside the network is mirrored.
Please do not ask me where this strange resistor values come from.
