[TenTec] QA - Filters:

[Dr. Gerald N. Johnson, electrical engineer]

I have, on several occasions. You might check the archives or ask again
tomorrow. Its too late tonight to type all my opinions. There are
crystal lattice filters and ladder filters (Tentec uses ladder filters)
with inherently different frequency and time response curves that have a
great deal of effect that I've seen over the past 40 years.

Ceramic can be good or poor, the tolerances are wide and the resonator
quality relatively low compared to good quartz crystals. Ceramic filters
are made with fairly sharp amplitude response shapes or with good data
passing responses. Sharp corners and data are mutually exclusive.
Crystal lattice and Collins mechanical filters tend to be designed to
similar Tchebychev amplitude response curves which incur rapid phase
response change at the pass band edges that lead to distortion of
digital data and ringing when hit by impulses, such as ignition noise,
the short spikes (at 360 Hz rep rate for three phase) of power line
noise, and the static from local or distant lightning. Ladder filters as
used by Tentec tend to have rounded shoulders and hence (based only on
the amplitude response which I believe to be short sighted) to have a
"poorer" shape factor than lattice or mechanical filters. My next radio
will have more rounded corners for even better prevention of ringing
from line noise and ignition noise. Thunderstorm static may not be as
much a problem for its 144 MHz operating range.

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