[Hallicrafters] ? Unusual filter in SR-400

[Walt Cates]

I am
looking for information on vintage FILTECH xtal filters used in the SR-400. All
of the Filtech filters in the 400’s have the Filtech logo and the Hallicrafters
part # stamped on them. 

I am in
the process of upgrading a level 1 Cyclone 400 to a level 7 Cyclone II. This
400 is one of the first built, the 11th one to get a serial #. While
checking my work I noticed that the input and output of the xtal filter read
zero ohms to gnd. I checked my other three 400’s and they are all open to gnd. 

I pulled
the filter in question and found first that it was marked different than all
the others. Along with the H part # and the Filtech logo there were the
following markings.

          CRYSTAL FILTER

            FILTECH
P/N 3121065

            C.F.
1650KC USB

Then I
put the filter on the test fixture and it tests perfect.

Passband
= 500 to 2800Hz ( 1650.500 to 1652.800KHz )

Insertion
loss = 2.3db.

So
the filter works perfectly but this filter is a much different animal from all I
have seen before. The rig works and quite well but this is puzzling.

 

Best Regards, Walt Cates, WD0GOF
 
 GOD put you here because there is something no one else can accomplish.