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The NE602 is an fantastic integrated circuit, complete one chip radio!
The NE602/SA602/NE612/SA612 family, all have inside, an oscillator and double-balanced mixer.
It can be used too as the 2nd mixer in a dual conversion receiver, and as a balanced modulator.
With addition of the TA7642, increased simplicity of the circuit, contributing with IF high gain, selectivity and demodulation for AM signals.
With the schematic below, this single conversion radio, was possible to achieve 12dB of SINAD with RF signal of 5uV at 14.000 MHz!
With addtional tuned cascode preamplifier ( not showed ) with two MPF102, was possible obtain 11dB of SINAD with 1.24uV !
After the implementation of an good match at input circuit with wideband core T50-52, the sensitivity go to 1.0uV with SINAD of 12dB!
Teste with the loopstick antena can be done in two band, MW and SW.
To achieve great performance, was used the cascode preamplifier.
The above loopstick antenna and oscillator coil was removed.
With the schematic below, the T50-52 core ( broadband tranformer) was used in the input cascode preamplifier and T50-2 for the oscilator.
The RF sensitivity was increased, to obtain best performance.
The 455 kHz ceramic filter insertion loss, contribute to reduce the SINAD.
This filter was selected to the best low insertion loss.
Another fact, the TA7642 bias is important to maintain the gain and lower the SINAD.
Near fluorescent lamp with electronic reactor, computer and switching mode power supply, introduce noise and reduce drastically the performance performance test!
For guarantee, all this devices near the radio must be in off, during the test and operation too!
Thank you to visit!
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