Table 1 (Continued)
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 the main frequency slightly, since
PEAK and NOTCH may not track perfectly. For two whistles, or CW, or teletype QRM, use
both main and Aux Notch.
Weak CW
An AC voltmeter, or scope, across the filter output is a big help in peaking weak CW.
Strong Signal
A flat response is approximated with the Aux Notch at 11,000 and main filter as follows:
PEAK: Freq. = 12 o clock; Sel.= Min.
NOTCH: Freq. = 2500; Sel. = Max.
LOWPASS: Freq. = 2500; Sel. = Min.
HIGHPASS: Freq. = 250; Sel. = 2 o clock
Note: Even with these settings the filter contains additional fixed rolloffs below 250 Hz and
above 2500 Hz, so is not intended for Hi-Fi applications, only communications.
TTY, SSTV
and Misc.
For TTY, SSTV, etc. reject low frequencies using HIGHPASS: Sel. and Freq. about 10-12
clock (experiment). Or use notches to reject CW, etc.
You will no doubt discover other settings for voice, CW, etc. not in this table, but useful under
some conditions, or with your own ear preferences. There is a conceivable use for almost all of
the infinite number of settings under some conditions, and with some signals.
Line Noise,
Ignition, or
Other Static
The QF-1A will produce some improvement due to narrower bandwidth, especially on CW, but
nothing dramatic on voice. The only really good solutions are a good IF NOISE BLANKER in
your receiver, or a beam antenna. Even IF blankers are generally ineffective except on car
ignition noise -- and may help a little on line noise. Audio NOISE LIMITERS (not to be
confused with IF BLANKERS) can be built for the cost of two 5-cent diodes (see Radio
Amateur s Handbook), but we found them to cause distortion and be virtually worthless for
noise, so they are not included, despite their negligible cost.
NOTE 1: AUX NOTCH SETTING. It s usually best to leave the Aux Notch at 11,000 until the main filter is
adjusted for best results. Set it at about 9 o clock for voice, where it rejects a wide band of hiss and high-
frequency whistles. Set it to reject any loud whistle or CW at other frequencies.
