Note
The AF-406 and 606 are visually identical, and nearly identical in functionality. The big difference is that the AF-606 includes a phase locked loop function. Except for the PLL, the following discussion applies to both models.
The basic modes of operation are:
NOTCH : A 20dB notch, with a bandwidth adjustable (rear panel preset) from 50–600 Hz tunable over the range 0.3- 3.0 kHz.
SSB : Bottom limit set by a high-pass filter with a 500 Hz –6dB point and 12 dB per octave roll-off. Upper limit selectable from 2.5 kHz, 2.0 kHz and 1.5 kHz (–10 dB) with roll-off of 12 , 24 and 36 dB per octave respectively.
CW : The piece-de-resistance, a phase-locked loop filter with an input range tunable from 0.5 to 1.2 kHz , and a lock range of 70 Hz. When the tone frequency of the received CW signal and the free-running frequency of the PLL tone decoder are the same, a locked signal output is generated which flashes the LOCK LED and keys an audio oscillator to reproduce the CW signal free of interference caused by noise or fading.
All controls mentioned (except for notch bandwidth) are on the front panel, along with the ON / OFF switch, which bypasses the unit for audio in the OFF position, and a phone jack.
Other items on the rear panel are PLL audio oscillator pitch and volume controls, plus the DC supply jack and phono sockets for audio input and external 8 ohm speaker (an internal speaker is included). with a maximum output level of 1.7 watts. The audio input level required is a nominal 2 volts (0.5W into 8 ohms) with a minimum of 1 volt for reliable PLL operation, and a maximum of 4 volts.
The unit uses a total of seven ICs (three of them quad op amps) and one transistor.
Power: 12–15 VDC at 200 mA.
