[Boatanchors] Low Pass Filter Comparisons

[Peter Markavage]

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