User manual
Table 1 (continued)
Weak CW
An AC voltmeter, or scope, across the filter output is a big help in peaking weak CW signals.
Strong Signal
A “flat” response is approximated with 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.
RTTY, SSTV
and Misc.
For RTTY, SSTV, etc. reject low frequencies using HIGHPASS sel. And freq. About 10-12 o’clock (experiment.)
Or use notches to reject CW, etc.
You will doubt discover other settings for voice, CW, etc. not in this table, but useful under some conditions or with
you 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 I.F. Noise Blanker in your receiver, or a beam antenna. Even I.F.
blankers are generally ineffective except car ignition noise – and may help a little on line noise. Audio Noise
Limiters (not to be confused with I.F. Blankers) can be built with two diodes (See Radio Amateurs Handbook), but
we found them to cause distortion and 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 or hiss and high-frequency whistles. Set it to reject any loud whistle or
CW at other frequencies.