[TowerTalk] coax stubs /bandpass filter

[Dave - AB7E]

Certainly.  Why would you think otherwise?  You just need low loss components.  Air wound coils would handle high power easily, but it's a bit trickier to find capacitors that handle high RF current.  I bought some high power strip line RF capacitors for a couple of filters that I have yet to assemble, but there are other ways to do it.  If you don't think it can be done, check out the filters sold by Array Solutions.

And of course not all filters need to be high power.  Those that protect a receiver from out-of-band damage can have much less power capability ... a couple hundred watts even if it needs to handle the outgoing power of a transceiver.

Dave   AB7E




------Original Mail------
From: <k2qmf at juno.com>
To: <towertalk at contesting.com>,
    <towertalk at contesting.com>
Sent: Tue, 30 Mar 2010 13:52:07 -0400
Subject: Re: [TowerTalk] coax stubs /bandpass filter

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 at 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 at karlquist.com>
> To: "Tower and HF antenna construction topics." 
> <towertalk at 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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