Table 1. USEFUL ADJUSTMENTS
Your QF-A can imitate the response of virtually any filter with fixed responses, at any price, and give an infinite
number of other useful responses as well! Truly, if the QF-1A can t pull the signal out, no other filter can either!
However, the QF-1A s flexibility means that even experienced operators will need some time to learn how to best
use all the controls. The following table will aid you. IMPORTANT: Don t give up on a setting because it doesn t
seem to help. Tomorrow, with different conditions, this setting may turn out to be just what s needed.
Condition
Useful Adjustments (See Note 1 for Aux Notch setting)
PEAK. Casually listen with 7 to 10 o clock selectivity, yielding a relatively wide 80 to 120 Hz
bandwidth. Adjust frequency for desired CW note. Gradually increase selectivity and touch-up
frequency to match conditions. There is much confusion among hams about ringing of a CW
filter, mainly caused by mfrs. of filters without the narrow ultimate selectivity of the QF-1A.
Basically, here is the truth: ALL filters will produce audible ringing at bandwidths below 80-120
Hz (and many poorly designed filters will ring even at wider bandwidths). So the only way to
eliminate ringing is to use wide bandwidth (low selectivity on the QF-1A). On the other hand, a
CW signal has a bandwidth less than 10-20 Hz, so a very narrow filter can pass the entire CW
signal and greatly reduce interference -- but at the expense of ringing. The QF-1A gives you
your choice (at considerable increase in manufacturing complexity). High selectivity will be
found to be invaluable in very heavy QRM or pileups, allowing you to hear signals inaudible at
wider bandwidths, but high selectivity is not as useful in thermal noise. Note that gain at the
peak increases at high selectivity, while blasting when the desired signal comes through the
narrow slot .
Desired CW
Signal
LOWPASS. Produces an effect similar to PEAK at high selectivity. Ignore LOWPASS Sel.
panel markings for CW reception. If you listen to CW at a low note (more than 12 o clock freq.
rotation), you may find that you prefer LOWPASS. But LOWPASS is wider, and gain varies
more.
Voice Signal
with Splatter
LOWPASS. Adjust selectivity as on panel: rotate frequency for best compromise between
rejection of splatter and rejection of desired signal. Frequency rotation beyond 8-10 o clock
rejects desired signal heavily, making it sound bassy. The idea is to find the best cutoff
frequency, to maximize copy. If splatter completely covers the desired signal, or if two signals
are on the same frequency, the situation is impossible, and no known method of signal
processing will work.
PEAK. This position, at moderate selectivity of 7-9 o clock, and frequency adjusted for best
copy, can sometimes clean up signals and give more presence .
Voice Signal
(Moderate
Interference)
HIGHPASS. Full frequency rotation (250 Hz) and 3-5 o clock selectivity, along with AUX
NOTCH at 9 o clock, can give greater presence under some conditions. To reject lows or
hum, set frequency as little as 11 o clock, with selectivity rotated about 2/3 of frequency.
