[Boatanchors] Low Pass Filter Comparisons

[EP Swynar]

Hi Peter,

I believe it was written-up in QST way before 2002 --- probably sometime in
the early 80's, because after I read the piece, I went out & bought a B&W
filter for a linear amplifier project that I was working on at the time...

As I recall, the piece even showed 'scope photos of the actual cut-off
characteristics of each filter. It was a very good read.

~73~ Eddy VE3CUI - VE3XZ


****************************************

----- Original Message ----- 
From: "Peter Markavage" <manualman at juno.com>
To: <boatanchors at mailman.qth.net>
Sent: Wednesday, November 12, 2008 1:33 PM
Subject: Re: [Boatanchors] Low Pass Filter Comparisons


> I just checked the QST/QEX/Ham Radio archives, and the only write-up on
> various kinds of low-pass filters was done in August QST 2002, page 62.
> B&W and Drake weren't covered. There were lots of homebrew articles on
> developing low-pass filters. I did not check the 73 or CQ magazine
> archives.
>
> Pete, wa2cwa
>
>
> On Wed, 12 Nov 2008 11:25:07 -0500 "EP Swynar" <gswynar at durham.net>
> writes:
> > Hi Glen,
> >
> > The old Barker & Williamson low pass filters were supposed to be one
> > of the
> > best made, too...
> >
> > Indeed, some years ago there was a very detailed writeup in QST
> > comparing
> > many different brands of LP filters, & B&W ranked right up there, as
> > I
> > recall.
> >
> > ~73~ Eddy VE3CUI - VE3XZ
> >
> >
> > ************************************
> >
> > ----- Original Message ----- 
> > From: "Glen Zook" <gzook at yahoo.com>
> > To: <boatanchors at mailman.qth.net>; "Peter Markavage"
> > <manualman at juno.com>
> > Sent: Wednesday, November 12, 2008 10:08 AM
> > Subject: Re: [Boatanchors] Low Pass Filter Comparisons
> >
> >
> > > One thing that has definitely helped with the TVI complaints is
> > the
> > widespread use of cable television these days.
> > >
> > > My main linear is a Tempo 2001 (pair of 8874 tubes) that,
> > unfortunately,
> > was poorly designed, at least in terms of physical layout.  I was
> > traded my
> > 2001 brand new back in the 1970s and immediately found out that it
> > had
> > problems.  Things like the final tank coil is right next to the
> > power
> > transformer with NO shielding between, almost no bypass capacitors,
> > etc.
> > The only shielding was the cabinet cover and that did not make
> > physical
> > contact to the chassis because of heavy paint.  Now the TVI problems
> > were
> > before cable television, but I leave the filters in place because
> > there are
> > still a couple of my neighbors that don't have cable even though it
> > has been
> > available for almost 30 years!
> > >
> > > It took a lot of work but I was finally able to completely
> > eliminate TVI
> > from the Tempo 2001.  But, it took 2 of the Drake filters (in
> > series) to get
> > rid of the last of the TVI.  I do have one on the output of my Heath
> > HA-10
> > Warrior, on my Heath Apache, Heath DX-100, and a spare, or two.  All
> > of
> > those transmitters are "clean" with the Drake filters in place but
> > do cause
> > slight TVI on my television sets without them.
> > >
> > > I tried the Yaesu filter on the Tempo linear and although it does
> > help
> > some, it is no where near as good as a single Drake.  Now I have
> > not
> > actually made any "real" measurements of the harmonic reduction.
> > But, the
> > fact that TVI has been completely eliminated with the Drake filters
> > is a
> > fairly good indication that they are doing the job.
> > >
> > > Glen, K9STH
> > >
> > > Website:  http://k9sth.com
> _______________________________________________