LA1235

No.873-11/12

Cain distribution of application circuit

If IC anone is operated without front end, the tuning meter deflects toward plus side at the time of no input. This

phenomenon is caused by the fact that the noise component to be applied to the quadrature multiplication circuit is not

syummetric with respect to 10.7MHz but is shifted toward lower frequency side because the frequency characteristic of

IF amplifier attenuates at high frequencies and the phase shift circuit is of low-pass type. If the formt end is attached and

the noise which passes through the narrowband filter of IF stage and spreads symmetrically with respect to 10.7MHz is

stronger than the noise generated inside the IC, the tuning meter reads 0.As the gain of the front end is decreased, input

limiting sensitivity and usable sensitivity worsen abruptly. This phenomenon is caused by the fact that since the tuning

meter is set to 0 at the time of no input the tuning point of the quadrature circuit must be shifted toward lower frequency

side than 10.7MHz and the demodulation output waveform is deformed asymmetrically at an input in the vicinity of

usable sensitivity. However, if the gain of the front end is too increased, the signal meter poiter does not return to zero

point at the time of no signal.

Sample Application Circuit

Unit (resistance :

Ω, capacitance : F)