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7 MHz SSB Transceiver

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MC1496
Double Balanced Modulator

mixer

A mixer is a nonlinear element that combines two signals. A mixer has three ports: F1 receives low level signal; F2 is high level signal (local oscillator) and F3 is the resultant mixer product.

The output of the mixer contains number of different frequencies that obey the relationship   Where m and n are integers 0, 1, 2, 3,...

There are three types of mixers: single-ended, single balanced and double balanced. Double Balanced Mixer (DBM) suppresses F1 and F2 components of the output signal leaving only the sum and difference frequencies. Double Balanced Mixer provides superior suppression of the local oscillator and RF signals in the output leaving only the sum and difference frequencies. This is known as port to port isolation

MC1496 is an active double balanced mixer made from bipolar silicon transistors formed into Gilbert transconductance cell. The internal circuitry of MC1496 DBM is given below.

Internal Circuit of Double Balanced Mixer MC1496

MC1496 is available in 14-pin DIP package. Brief descriptions of various pins are given below.

MC1496

Pin 1 and pin 4 are balanced low-level inputs. Pin 8 and pin 10 are balanced high-level inputs. Pin 6 and pin 12 are outputs. Pin 5 is bias usually connected to Vcc through a resistor (normally 10k). Pin 2 and pin 3 determines gain of the mixer. The gain will be maximum when pin 2 and pin 3 are shorted. Gain can be adjusted by connecting some resistance between pin 2 and pin 3. Pin 7, pin 9, pin 11 and pin 13 are not used.

DC Voltage measured at various pins of MC1496 given below. There may be slight variation in these voltages due to accuracy of measuring equipment or components used.

PIN VOLTAGE PIN VOLTAGE
1 3.58V 8 6.51V
2 2.96V 9 NC
3 2.91V 10 6.51V
4 3.58V 11 NC
5 1.25V 12 11.8V
6 11.81V 13 NC
7 NC 14 0V [GND]



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