HELP: 9 MHZ roofing filter

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HELP: 9 MHZ roofing filter

Postby G7LQY » Sat Jan 21, 2012 7:26 pm

Hi all
thinking of place a 9mhz roofing filter after the first mixer (SBL-1)in the rcvr.
but it will have to have a BW of about 16khz!, to allow for FM BW
i was thinking of designing a 9 MHZ roofing filter with a BW of 16khz, with 9mhz crystals
can anyone help with such a design ?
Posts: 42
Joined: Wed Apr 29, 2009 4:21 pm
Location: Bury, Lancs UK - IO83UO

Re: HELP: 9 MHZ roofing filter

Postby iw3sgg » Fri Mar 30, 2012 2:26 am

I'm building severals filters last year.
I suggest to you:
1)download the program Dishal on the web
2)Buy 20-30 crystals on ebay.
3)Test the crystals with G3UUR method
4)Select 10 crystals after test
5)Start with program Dishal with QER filter (more simple) that ladder type.

Test set do you need:
1)Good LC meter (more accurate)
2)Spectrum analyser with tracking generator to test the filter or VNA
3)A lot of self control.

Build a good filter is not simple,the program help you but after build it you must test and correct it for a good result.
Same images of one filter that I build.
To measure the crystals I use the G3UUR mode,I built an oscillator for
crystals ad with program dishal I select the crystals.
Sorry for bad English!!!!
For information or same images we could write to iw3sgg@ir3arp.net

73 de iw3sgg Noris.
Whith mini VNA the response of filter after one night of modify.
(26.7 KiB) Downloaded 367 times
Crystal filter QER type 7 pole.
QER7P.png (5.1 KiB) Viewed 4857 times
Board of crystal filter
QER7PBoard.png (15.16 KiB) Viewed 4857 times
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