The IF signal is amplified by a single transistor stage and audio is recovered using a biased shotkey diode and JFET buffer transistor. The LM audio amp is used to drive a small 2. The circuit contains four LC tuned circuits, all of which need to be fine tuned to obtain good results. An oscilloscope and RF signal generator are useful, but the circuit can also be setup using local radio stations and an additional portable AM radio.
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Pin configurations of the mixer Here are the pin configurations of the mixer in figure 1 below. IN b Pin 2 The other half of the balanced input. Ground Pin 3 Output high is about 1. Oscillator base Pin 6 This is the input to the base of the oscillator transistor. See data sheet for comprehensive explanation. Oscillator emitter Pin 7 This is the input to the emitter of the oscillator transistor.
Note comments about effective supply filtering and bypassing this pin below under "General considerations with using a mixer". Block diagram of the mixer Figure 2 - block diagram of the mixer General considerations with using a mixer Vcc should lie between 4. Input signal frequency is typically up to about Mhz, while typically the oscillator will work beyond Mhz.
At 45 Mhz signal input the noise figure is quoted as 5. The output impedance of the mixer pins 4 and 5 is 1K5 1, ohms and the mixer needs to see that impedance.
The SAA is designed for optimum low power performance. The RF inputs Pins 1 and 2 are biased internally. They are symmetrical. The equivalent AC input impedance is approximately 1. Pins 1 and 2 can be used interchangeably, but they should not be DC biased externally. This is NOT an exhaustive list of all possible configurations. From transformer theory we know this is going to be the square of the turns ratio we decide to use. Of interest to people constructing DC Receivers is the schematic in fig 3-d.
Here is a balanced output of audio frequency which we would feed to a suitable audio amplifier such as the LM series of devices. This way you get all the needed information. Pay by PayPal or check! This includes both fixed and variable oscillators as well as fixed and variable crystal oscillators - all in the HF region. Note that up in the VHF region it is almost impractical to design variable oscillators, the drift will kill you. Google Custom Search Got a question on this topic?
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NE602 or NE612 DOUBLE BALANCED MIXER