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Technical Topics => The RF Workbench => Topic started by: N9QIW on December 05, 2020, 0433 UTC

Title: 22 meter low pass filter design
Post by: N9QIW on December 05, 2020, 0433 UTC

Does anyone have a design schematic for a 13.56 mhz a simple low-pass filter? I can always look at the various online calculators,  but just curious if anyone has a schematic that they like to use/has proven history.  Thanks in advance.   I'm in the process of building/programming/testing a 22 meter WSPR transmitter.

Title: Re: 22 meter low pass filter design
Post by: ThaDood on December 05, 2020, 0715 UTC

Well, yeah!!!! Just copy the one that I made for this 13.560MHz milliwatt TX,     http://boomerthedog.net/13560.html   Scroll down to the bottom for the two page .PDF schematic, then check-out the Chebychev Filter that's at the end of Q3, and between TP3 and TP4, on the LPF Board. All built from salvaged parts as well. Good luck!!!

Title: Re: 22 meter low pass filter design
Post by: NJQA on December 05, 2020, 1445 UTC

I would think that any 20 meter LPF kit would work.  There are a number of them designed for QRP from places like qrp-labs.com and qrpkits.com that are very inexpensive.  I would expect that the second harmonic from 22 meters would be as well supressed as would that from 20 meter signal.

Title: Re: 22 meter low pass filter design
Post by: N9QIW on December 06, 2020, 0626 UTC

Thanks ThaDood and NJQA for the advice.  I absolutely enjoyed reading the hand-drawn schematic you made ThaDood-lots of work involved and good job getting the thought process down on paper.  NJQA- Great minds think alike.  The 20m LPF crossed my mind as well.   Both of you thanks again for your advice and input. 

Title: Re: 22 meter low pass filter design
Post by: Stretchyman on December 07, 2020, 2213 UTC

https://rf-tools.com/lc-filter/

Simples..

I'd get used to LSPICE too..

Str.