Data transmission by frequency division multiplex methods - uses integrator circuit for trapezoidal wave shaping to avoid interference

摘要

The method and circuit are for the transmission of data over a frequency division multiplex network using a modem and avoiding problems such as increasing adjacent channel noise, beating with group pilots when the data channel is the first or sixth in the group. The square wave pulse of T/2 and width peak voltage Vi is transmitted to line in a trapezoidal form with leading edge rise time and trailing edge decay times of (t1) each which is inversely proportional to (DELTA F) and avoids pilot interference, where (DELTA F) is the carrier to pilot frequency difference. and 2 t1 + t0 = 2/DELTA F + t0 where t0 is the pulse width at peak when trapezoidal. The circuit to modify the pulse shape uses a differential amplifier (A) as a Miller-Integrator with input resistor (R1) and input/output capacitor (C1). Parallel to the capacitor (C1) are a switching diode (D1) and a switching transistor (TR1).