[TenTec] Orion, NRD-545, DSP, filters etc

[Dr. Gerald N. Johnson, electrical engineer]

In my experience, most crystal lattice filters ring adversely when hit
by pulses, such as noise or fast CW. Tentec uses ladder filters that
have a less square frequency response and as a consequence have a more
linear phase response and thus ring much less.

My audio DSP, a Timewave DSP-59+, has a far superior selectivity without
rapid changes in phase response, and with noticeable detectable ringing
on 35 wpm CW at bandwidths above 50 Hz.

The DSP filter can be built to have very good selectivity at the same
time it has linear phase response and that is what it takes to make a
filter not ring. Its easy in a DSP filter to have many poles, while in
an analog filter having many poles can result in excessive insertion
loss and cost. Most analog filters have to trade off selectivity and
skirt steepness for ringing. Most amateur radio filters (crystal lattice
and mechanical) choose steep skirts sacrificing ringing. Tentec crystal
filters sacrifice some corner sharpness in trade for much less ringing.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.