[OFARC] FW: Band Pass Filter project

[Dominic Mazoch]

 This shows why live training is a good thing.  Dominic Mazoch

---------- Original Message ----------
From: ralph phillips <ke5hdf at sbcglobal.net>
To: MLandress via OFARC <ofarc at mailman.qth.net>
Subject: [OFARC] FW: Band Pass Filter project
Date: Sat, 6 Nov 2021 12:50:55 -0500


 
During the weekly net last Tuesday, the idea of band pass filters was raised.
I have the files and parts for the project we did a few years ago.
 
The note below briefly describes the band pass filter project we did.  These filters have 0.5dB (or less) insertion loss and VERY steep cut off.  
 
Basically, you wind coils on PVC forms and mount them in a metal enclosure.  We took the guts out of old computer power supplies and used the boxes.  Capacitors are then added per the schematic.
Also, I have attached the design files for a 20m filter and a spreadsheet of capacitors that  work well.  (the first set I used has too much internal resistance and got VERY hot. These worked much better)
 
If someone wants a different band, I have designs for 10m, 40m, 80m and 160m.
 
Let me know if there are questions.
 
Ralph
KE5HDF
 
From: ofarc-bounces at mailman.qth.net [mailto:ofarc-bounces at mailman.qth.net] On Behalf Of Ralph (home)
Sent: Thursday, August 10, 2017 10:09
To: OFARC <ofarc at mailman.qth.net>
Subject: [OFARC] FW: Filter project
 
Again &hellip;. Band pass filters block radio frequencies above and below the band you want.
So &hellip;.  The 20m band extends from 14.0 mhz to 14.35 mhz.  The filters we built last time block everything higher frequency than about 15mhz and lower than 13.5 mhz.
That eliminates the 7 mhz harmonics from 40m and the 28 mhz harmonics of 10m.
 
The filters we built before are simple &hellip;. Some coils and capacitors.
We found them on the web listed as the NVARC &ldquo;Ugly filter project&rdquo;
Here is the web page&hellip;.   https://www.n1nc.org/Filters/
All details for several bands are included on the pages.
 
The capacitors they list are  no longer available, but the technicians at Mouser.com (electronics parts) helped me find some replacements.
 
There seems to be a consensus to build the 20m and 40m band pass filters.
I have decided to just use the same part numbers we had before&hellip;. Go for quality
The cost of capacitors is $16+shipping for each 20m or 40m filter.
 
We will make the coils ourselves from wire wrapped on pvc pipe.
 
Other parts needed &hellip;..a metal box , 2 coax connectors, solid copper wire, pvc pipe, misc. screws and nuts.
 
I expect the total cost to be $35-$40 per filter (assuming my previous source of boxes is still  open)
We can take a head count at the next club meeting and order parts
I will bring a filter and explain the fabrication techniques I used.
 
Ralph
KE5HDF &hellip;
 
P.S.     If anyone wants a filter for a different band, I can help them find suitable parts at Mouser.com
 
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