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Band Pass Filter Fever – The Tangled Web – Part 1

Amended 3/25/2012: Again – re-Fixed broken links, added new links for VK4EMM and KG4JJH reference material

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On occasion I’ve noticed I have a tendency to get wrapped up in an idea I can’t shake. Obsessed might be a close description despite the negative connotations. It’s not quite an obsessive mania, nor is it complete fixation. Perhaps fascination is closer to the truth. A “passionate fascination” sure sounds better than “obsession”. Not much difference semantically, but there it is.

Oddly enough, the most recent subject of interest is band pass filters for HF. (Reeks of geek, no?) Conjured by both this year’s(2008) Field Day and the IOTA operations, it is something I became interested in out of need. Commercial filters are available. It also seems that it is still possible to home brew decent band pass filters for relatively low costs. There are several designs widely available. Using coaxial stubs is also an option.

Homebrew is more fun, and in this case, possibly even less expensive. The difficult part of the problem for me is a simple method for tuning the filters. I don’t have access to a lot of test equipment. Also, some of the designs are easier to build than others. Selecting appropriate parts is also a bit of a problem in some cases.

Ideally, a good band pass filter will have a low insertion loss over the pass band, and a high level of rejection outside the pass band. I’m no Werner Von Einsteeen electronics whiz, but there are going to clearly be some trade-offs there somewhere. So knowing your application can guide you to deciding which trade-offs are appropriate.

A look at commercial filters is also helpful. It i$ certainly ea$ier to buy off the $helf filter$. Filters are available from Dunestar, I.C.E., and the W3NQN filters from Array Solutions. I’ve also run across a set of high power filters, but can’t find the link. EU I think. 4O3A also has a version of high power filters.

In an article by Peter Pfann, DL2BNU (German language only)of the Bavarian Contest Club, there is a chart of test results as conducted by DL2BNU. Peter’s chart, page 3, shows the measured insertion loss for most of the filters on each band, lacking only measurements for the I.C.E. filters on 80m or 160m. His chart highlights some of the trade-offs. The Dunestars have better attenuation outside the pass band, but at the cost of higher insertion losses. The I.C.E. filters are least expensive and have low insertion losses in the pass band, but generally show slightly less useful attenuation in the adjacent bands.

I expect to need two sets of filters. I’d like to have them for exploring SO2R as well as for use at Field Day and IOTA. All of that operating is at low power. So – a low pass band insertion loss is desirable.The other significant considerations include total cost, availability of suitable components and materials, and ease of assembly. Finally – they need to add value by !FILTERING! That’s the whole point, right?

Proceed to Part 2 -Band Pass Filter Fever – Untangling The Web, or follow some of these additional references below.



Primary web references:

The Nashoba Valley Amateur Radio Club, the NVARC “Ugly” filter project, by W1FP and KD1LE.


Article by Peter Pfann, DL2BNU of the Bavarian Contest Club, a construction project write up on building the W3NQN filters.

RF Filters, ARRL Technical Information service page with filter definitions and article references

Band-Pass Filters for HF Transceivers by Lou Gordon K4VX QST September 1988

W3LPL Receive Only Band Pass filters via K1TTT technical references site.

K2TR Coax Stub Filters via K1TTT technical references site.

K3NA Coaxial stubs via the K1TTT technical reference site

Clean Up Your Signal with Band-Pass Filters, By Ed Wetherhold, W3NQN 1998 ,[ARRL Members only] 2 parts [ –Part 1– , –Part 2– ].

Additional references:

Excellent advice from KG4JJH about building and tuning W3NQN filters.  (added 2012/03/03)

Band Pass Filters for Contesting by Brian Bartlett, VK4UM and John Loftus, VK4EMM

QST Product Review of Dunestar commercial filters Dunestar Model 600 Multiband Bandpass Filter, QST March 1995

Dunestar bandpass filters

Array Solutions commercial filters based on W3NQN QST article June 1998

Industrial Communication Engineers LTD, ICE commercial bandpass

Inexpensive Interference Filters by Alan Bloom N1AL, QST June 1994 (ARRL members only)

Narrow Bandpass Filter [ARRL Members only] article in QEX by William E Sabin W0IYH

Band Reject Filters by AF4Z

amended, 9/15/2008(tnx K9ZW!) :

“Managing Interstation Interference – Coaxial Stubs and Filters” by George Cutsogeorge, W2VJN, available in hardcopy from International Radio for only $15 USD.

amended, 3/31/2010:

K9YC, Some Q&A About Coax and Stubs for your HF Station. Good stuff.

Amended 9/30/2010: Fixed links broken by ARRL website re-design

Circular Link-amended, 7/06/2009:

This excursion into filters turned into a series of musings, so there is more on the process andmethods of discovery as I re-invented the wheel. It is a circular link because it also takes you back here. Oh No!


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