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Re: RE: Another interesting preamp story

> If you cannot find a 1 inch square (brass or copper) I suggest to cut
> two copper sheet 1/16-inch thick  6" long and 2" wide and bend it at
> 90 degrees in a vise after that you can solder both angulars all the
> way long to form a 1" x 1" square tube 6" long and if you use copper
> you don't want to silver plate the filter.
> Have fun and 73" de
> i8CVS Domenico

Hi all,

 I constructed few days before this filter as Domenico, i8CVS suggested to
me and
it works perfect, is excellent!

 But as above mentioned the 1'' square tubular brass (or copper)  is
unavailable also here.

I found a similar to Domenico's method in order to make the filter, at my
opinion more practical,  because there is no necessity to bend the copper
by 90° as mentioned above.
This method needs definitely a good bend-tool.

So, I bought a brass corner-piece with 3cm in height per each side (thick =
1mm or 1/25'' ).
3cm = 1.18''  but larger corner-side is also welcome as does no have any
importance (read below why). This brass-corner I found it easily in a local
General store.

 I cut 2 corner-pieces 6'' long each one which is the overall length of
filter. The first one
corner-piece (only this one) was cut in order each side (in height, wide)
becomes equal to 1'' by using a snips. Thus, by soldering this smaller (in
height of each side=1'') into the other piece with bigger sides, is possible
to make a square tubular with internal diameter = 1'' (or any other diameter
you wish).

  This method helps also in BNCs, trimmer and diodes arrangement when the
two corner-pieces
are separated,  in contrast with inflexible (monocoque) square-tubular where
this work is very difficult.

Thus, after the soldering of connectors, central conductor (L/2) etc is
possible to
open a hole  in order to pass the Hi-Q trimmer through the 2nd corner-piece
and we can measure carefully the various placement alignments, in order to
joint all components in the right place, as the 2 corner-pieces are still
"open" (unsoldered), so the internal-world of filter is viewed.

When all the components and materials have been placed in the right points,
solder permanently the two opposite corner-pieces between each other from
the begining up to the end of each opposite corner-side with a hi-power
solder iron. This work can be done from the exterior side, easily, without

Finally, I uncoditionally suggest a 2nd identical filter in the output of
your LNA.
Personally,  I have.... destroyed several times my GasFet preamp during
experiments and the protection of my preamp it was an unsolved problem for
me against to faulty PTTs, for a long-long time.
Now, I push my PTT with 25 Watts (my max.power) direct to my preamp's output
and the preamp still... working  perfect !  Incredible !
No problem, no more destroyed GasFets ! I'm very happy! Expept the Low-Loss
filter into the Input of preamp its also a pretty magic filter  for
protection due to fault PTTs, if connected a second one into the output of

 So, I would like to say A MILLION THANKS to Domenico, i8CVS for QSP !
Great help !

73, Mak SV1BSX


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