| 摘要 |
A direct modulation FM data receiver of the offset type in which the local oscillator frequency is located between the two signalling frequencies, deliberately folding the transmitted spectrum about d.c. in order to counter the effects of drift in the local oscillator, the receiver comprises a simple but effective AFC system wherein over the relevant frequency range, it has a non-linear discriminator transfer function and in use produces a voltage having a sign to adjust the local oscillator frequency in the correct direction. |
