[Boatanchors] Low Pass Filter Comparisons

[Carl]

I believe it was QST who did a comparative test on several LPF's several 
years ago.

Memory says that the Drake had the sharpest cut off frequency and the 
B&W the best ultimate rejection. The others were within their advertised 
specs and did the job in most cases.

Class C rigs of course are the worse offenders. Ive also used a pair of 
LPF's in the old days, especially for 6 M Class C rigs starting off with 
8 mc xtals using the smaller Drake 6M filter. When I went QRO I used the 
B&W 6M KW filter on the amp; I think thats still available but I use ICE 
filters these days for 6M

If CH2 was a problem the big Drake was the best at the 100W level but it 
suffered more loss than what I would tolerate.

Carl
KM1H


----- 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
>
>
> --- On Tue, 11/11/08, Peter Markavage <manualman at juno.com> wrote:
>
> From: Peter Markavage <manualman at juno.com>
>
> Way, way back in the late 50's and 60's, I used the TV-1000-LP's on 
> several rigs, and I guess they worked, since I don't recall any 
> neighbor complaints when TV's were very susceptible to TVI. Discarded 
> them some time in the 70's and haven't used a low pass filter since. 
> Still don't have any TVI complaints.
>
>
>
> _______________________________________________
>