An experimental fast acting AGC circuit

Conventional backward-acting A GC circuits acting fast enough to counteract rapid fading will, if stable, suppress neighboring voice frequencies. However, forward-acting AGC is inherently stable, so it can be made very fast by inserting a sharp cut-off filter in the control path. This permits the suppression of 200 cps. fading with negligible effect on the 300–3,000 cps. voice band. Analysis and tests show that fading modulation products are suppressed by about 20 db.