User manual
Table 1 USEFUL ADJUSTMENTS
Your QF-1A can “imitate” the response of virtually any filter with fixed response, 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 flexibility
means that ever 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 manufacturers 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 to 120 Hz, (and many poorly designed filters will ring even at wider bandwidths.) So the only
way to eliminate ringing is to use a wide bandwidth (low selectivity on the QF-1A.) On the other hand, a CW signal
has a bandwidth less then 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 background noise is reduced. So keep receiver audio gain low at
high selectivity to avoid blasting when desired signal comes through the narrow “slot.”
Desired
CW
Signal
LOWPASS: Produces an effect similar to peak at high selectivity. Ignore LP sel. Panel markings for CW reception. If you listen
to CW at low note (more than 12 o’clock freq. Rotation), you may find that you prefer LOWPASS. But LP 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 rotations 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 desired
signal, or if tow signals are on 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 adjust 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.
Multiple
Whistles
or CW
Normally, AUX NOTCH is used. But the MAIN NOTCH is deeper (to 70 dB), and can be made narrower (at high
selectivity). Use notch sel. Shown on panel. The notch is not as deep at high selectivity, so use minimum sel.
Rotation consistent with least rejection of desired signal. Note: To help find the notch frequency, momentarily
switch to PEAK at high sel., peak the whistle, then switch back to notch at moderate selectivity. Touchup whistles,
or CW, or teletype QRM, use both main and Aux. notch