Autek Research QF-1A Active Audio Filter User Manual
Each filter is thoroughly tested twice before shipment. Please read the instructions carefully for best results, and save them for future reference. If you require adaptors or other parts not supplied, please obtain these locally as we do not stock them. This switch and the Selectivity/Frequency controls adjust the response of the main filter (all but the Aux Notch). PEAK (band-pass) passes a narrow band of frequencies, and rejects others -- just the opposite of NOTCH.
C. USEFUL ADJUSTMENTS PICKUP OF YOUR TRANSMITTED SIGNAL See Tables 1 and 2. This should be extremely rare with the QF-1A, as layout and RF bypass caps are excellent, and show no sign of RF at 2 KW with the antenna 20 feet away and the cover off, in our tests. However, some shacks, especially using end-fed antennas in the shack, and/or extreme RF on the 115 VAC AC line may possibly interfere with any audio gear. Solutions in this case are: 1) Plug the filter into an outlet away from the transmitter.
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.
Table 1 (continued) Weak CW An AC voltmeter, or scope, across the filter output is a big help in peaking weak CW signals. A “flat” response is approximated with aux. Notch at 11,000 and main filter as follows: Strong Signal 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.
Table 2 (Condensed Version of Table 1): Condition CW Voice Splatter Voice Voice Whistle or other QRM Two Whistles RTTY, SSTV Function PEAK or LP LOWPASS PEAK HP To Reject NOTCH HP Selectivity 8 o’clock or more As on panel 7 to 9 o’clock 3 to 5 o’clock / 11 up N/A As on panel 10 to 12 o’clock Main Frequency For best copy 7-11 o’clock For best clarity 250 Hz / 11 up (use aux. notch to reject whistle) (use aux. notch to reject whistle) Same as sel.
E. WARRANTY AND RETURNS G. ALIGNMENT We back our products better than most companies -not just 90 days, but one full year. The circuit has two alignments. Neither should require adjustment unless disturbed, especially the Main filter tracking alignment, which is quite non-critical. The Aux Notch Depth alignment is more critical and sensitive.
H. LATE NOTES K. CREDITS If you wish the QF-1A to drive a speaker in “bypass” you must obviously connect the QF-1A input to a rig output which is capable of driving a speaker. (Some headphone outputs, but not all, can drive a speaker). When the filter is “on” virtually any high-level rig output can drive it. Original documentation provided by Autek Research.
Inside View of Autek QF-1A (Component Placement) Illustration shown includes after market modifications: DC power input jack connected to ON/OFF switch, LED power “ON” indicator, and audio input jack. Illustration intended for standard component placement in reference to schematic diagram.
Bottom View of Autek QF-1A PC Board As illustrated: Top-Right control = R4 (Aux Notch) and Bottom-Left 14-pin IC = U3
