[SECC] CW filters

[Gary Breed]

Hi guys,

Just a note about a recent project:  I put 300 Hz CW filters in my
ICOM 765s -- Rockwell-Collins mechanical filters, not the FL-53A.

With the stock 500 Hz filters, the '765 has end-to-end selectivity
of about 400 Hz. With the new filter, the bandwidth is 260 Hz. I can 
not detect any ringing or other effects beyond what a typical narrow
crystal filter would have. 

The doubly-good news:

1.  It's cheaper than ICOM or INRAD!  For a quantity of two, the
filters were $88 each, tax and shipping included.  And the price
goes down some more with larger quantities. Sure beats $135 or $150+
each.

2.  It's easy! The impedance of the mechanical filters is identical
to the FL-53A, so no matching or other electronic work was needed.
I think most 455 kHz crystal filters for other radios will be about 
the same -- 1500-2000 ohms impedance. These things are tiny, about
1-5/8 x 5/8 x 1/4 inch plus pins. I made an adapter with a scrap of
PC board to plug into the filter socket. Couldn't be easier.

For more info, you can check out their Web site:
http://www.collins.rockwell.com/otherbusinesses/collins-filters/
Click on "low cost series" for details on the type I used.

Ordering is direct from Rockwell, prepaid with a bank check. I will
be happy to coordinate a group purchase if there is any interest
(there's already one on the list). Let me know.

73, Gary
K9AY



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