) writes:
On Fri, 23 Apr 2004 03:29:53 GMT, "Paul_Morphy"
wrote:

There's a good article about building ladder filters in QRP Power. Designing
and Building High-Performance Crystal Ladder Filters by Mahkinson, N6NWP.
Was originally in QEX for Jan 1995. QRP Power also reprints an article by
W7ZOI, Refinements in Crystal Ladder Filter Design, from June 1995 QEX.

snipped for brevity
"The usef ful upper frequency limit is determined by the influence of stray
capacitances at frequencies above 10 MHz and by the limitations imposed on
the VFO circuit for multiband HF operation. Consequently, the recommended
frequency range for an HF SSB crystal filter is between 6 and 12 MHz.: The
remaining criteria for the crystal frequency selection are the crystal Q and
the price."

Don't tell Elecraft their 4.9152mhz filters can't work.

We've seen so much about measuring the crystals and then doing calculations
in recent years, that it's easy to forget that hams started using crystal
ladder filters about thirty years ago. Make that a quarter century ago.
The fifth edition of Pat Hawker's "Amateur Radio Techniques" (copyright
1978) and references a number of articles in the France and the UK from 1976
on.

Memory tells me that when such filters started showing up in US publications,
namely QST, it referenced at least some of those articles, but then with
time the key articles have become the later onesin QST.

The synopsis in ART shows some standard designs, and you are supposed
to scale the components for your choice of crystal frequency. And no
mention there (though perhaps it was in the original articles) of
matching crystals. This is rule of thumb work.

Michael VE2BVW