[Boatanchors] Low Pass Filter Comparisons

[Glen Zook]

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.