This is a 5.2 MHz crystal filter. I used the G3UUR method for determining the crystal's motional parameters. I then used Dishal and AADE software to design a 10 pole Cohn Min-Loss filter. I tested the bandwidth with an Antuino Scalar Network analyzer (thanks Farhan!) and a NanoVNA. I found the passband to be a bit tight for SSB, so I replaced the capacitors with caps of a slightly lower value -- this broadened the passband. It is still a bit tight, but the SSB audio -- while not enhanced or Hi-Fi -- sounds fine.
Passband filter shape as seen in the Antuino and in the NanoVNA. The -20 db line in the Antuino actually corresponds to no loss.
The schematic provided by the AADE software. Dishal software may have come up with better, more correct values for the capacitors.
The passband as predicted by AADE. Skirts so nearly vertical as to strike fear in the hearts of SDR owners!
Filter under construction -- waiting for the caps from Mouser.
First scan with the NanoVNA. Insertion loss looks very high but that is only because I am terminating the filter with resistors -- I just wanted to see the passband shape.
Nice work and illustration, OM!
ReplyDeleteVery nice, Bill. Thanks for the explanation of Wes Hayward's termination insensitive amplifier. Very helpful.
ReplyDeleteDoesn't a certain left coast gentleman have a collection of rude words for "Dishal" :-)
ReplyDeleteI found it interesting and useful to compare the AADE and Dishal values for the shunt caps, and then compare results with the actual build. I think Dishal did a better job at prescribing cap values that would yield the desired passband. 73 Bill
DeleteGood work Bill, very inspiring!!
ReplyDelete