Re: [TowerTalk] coax stubs /bandpass filter

[k2qmf@juno.com]

Dave,

Can you design a lumped element filter that
can handle 1.5 KW????

73,
Ted
 
On Tue, 30 Mar 2010 10:35:54 -0700 "Dave - AB7E"
<xdavid@cis-broadband.com> writes:
> 
> I also don't understand the seemingly single-minded fascination with 
> coax stubs.  It takes more than one stub to get the same attenuation 
> that a properly designed lumped element filter can provide, the 
> optimum location for the stubs is not typically convenient, and 
> stubs for the low bands use a LOT of coax (which is both expensive 
> and bulky).  And depending upon the application, the ability of a 
> lumped element filter to be either low pass or high pass instead of 
> just bandpass can be useful (such as for buffering a low band 
> antenna from a single-feedline tribander).  With a little thought, 
> you can pretty much design a lumped element filter (or combination 
> thereof) for any passband you want.
> 
> Software to design such filters is available free to hams.  Lots of 
> folks use ELSIE, but I also find the free program AADE 
> (http://www.aade.com/filter.htm) to be pretty nice.
> 
> 73,
> Dave   AB7E
> 
> 
> 
> 
> ------Original Mail------
> From: "Richard (Rick) Karlquist" <richard@karlquist.com>
> To: "Tower and HF antenna construction topics." 
> <towertalk@contesting.com>
> Sent: Tue, 30 Mar 2010 08:36:08 -0800
> Subject: Re: [TowerTalk] coax stubs /bandpass filter
> 
> I've given up trying to make the lumped element argument to hams.
> Too hard to change belief systems.
> Coax stub filters are firmly entrenched ham radio folklore,
> regardless of whether they make engineering sense.
> They are seldom if ever used for filtering in commercial HF radio 
> systems.
> 
> BTW, the argument about the Q being "too high" goes away
> with the realization of the difference between loaded and unloaded
> Q.  The harmonics property is only useful if you need to pass
> the frequencies between the harmonics, which is not necessary
> for ham use.
> 
> Rick N6RK
> 
> 
> 
> jimlux wrote:
> > Along a similar note..
> > 
> > The stub is just a moderate Q resonator that's easy to fabricate.  
> Why 
> > not put a lumped LC shunt trap across the feedline?
> > 
> > Too hard to get the Q low enough?
> > Doesn't have the nice harmonics property? (a coax stub for 40 is 
> also a 
> > stub for 15)
> > 
> > _______________________________________________
> > 
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> > 
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