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Electro Mavin Filters at 2235/2304...



Hey, for all of you guys out there who bought Electro-Mavin 2.415 GHz
filters to play with... I said I'd try snowflaking the units down
to see if I could get them to work at 2304...  It failed miserably...
but then I thought "dielectric"... That worked...

I used a 3-ring notebook divider (the curvy type at the beginning and
end of a binder) that is made of Polystyrene (Recycle code 6/PS)..
I cut a piece to fit snugly (press fit) into the box firmly (and evenly: 
important) against the teflon circuit board.  (If the L-bracket is taken 
off, the screws that held the L-bracket go into the case a little, and the 
polystyrene will be held in this way).  Form the plastic to get the "curvys" 
out of it first, and press in firmly with your thumb.

What this did for me (according to the same HP network analyzer as I 
measured the units with before) is shift the 2.4-2.5 GHz filter down to 
about 2.25-2.35 GHz.  This is useful for 2256 MHz LO filters, and *heaven 
help us* 2304 MHz terrestrial work.  I imagine that any (American anyway) 
polystyrene divider would be close enough to still have the same effect, 
given the thickness is the same.  (I'll get the calipers out tonight- but 
I'd guess about 1mm or so..)

Other ideas may be to use 15 mil teflon pc board with all the copper off, 
etc.. but this seems cheap and possibly repeatable.

The filter shape and the loss were almost exactly the same as before, just 
transposed down.  Oh, and it is easily reversible... pop out the dielectric 
insert.

Fun, fun fun...

Fred W0FMS

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