VHF mixer circuit with band dependent switching

Details VHF mixer circuit with band dependent switching VHF mixer circuit with band dependent switching

1985-09-20

1988-03-15

Griffin, Robert L.

Telecommunications

Receiver or analog modulated signal frequency converter

Frequency modifying or conversion

455323, 329101, 329103, H04B 128

Patent

active

047318767

ABSTRACT:
A mixer circuit with a conventional very high frequency circuit for the reception of color television bands I and III, which is connected dependent on the band and which is provided with an NPN transistor. The NPN transistor operates via a collector resistor onto a two circuit band filter. Moire interferences in the band I region expanded for CATV are avoided by having the mixer current used to 0.3 to 0.6 mA via a counter coupling resistor disposed between base and hot end of the resistor 4. Thus the self-interference in band I is reduced by a value of about 60 dB. In case of band III operation the corresponding switching voltage is fed via a series connection of a diode 6 and a resistor 5 to the base and thus the base level is lifted up to higher mixing current, since in band III self-interferences cannot occur in the case of the presence of signals.

REFERENCES:
patent: 2996680 (1961-08-01), Barry et al.
patent: 3064197 (1962-11-01), Ek
patent: 3458819 (1969-07-01), Cafarella et al.
patent: 4412353 (1983-10-01), Itoh

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