30m Band CW-Transceiver

Posted on May 19, 2012

This simple QRP transceiver for the 30 m band did not result from a detailed requirement profile. I simply had some NE592 broadband amplifiers in my junk box, waiting for an application. After performing some tests, that application was quickly found: The amps should become part of a superhet transceiver. There is need for amplification in several places in such a rig, starting from the IF, over to the AF, and up to the RF for driving a push-pull final. The high crystal frequency of 14318 kHz allows a pulling range of 20 kHz without special tricks. You can tune the reception range from 10100 kHz to 10120 kHz using the coil L2. Some tests with the number of turns of the coil are recommended here, such tests are commonplace when setting up a VXO.

30m Band CW-Transceiver
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The oscillator signal is coupled into the transmitter mixer through a small link winding on L2, so the Tx mixer can be driven symmetrically. I first tried a capacitive connection, for example 10 pF at pin 7 of IC 1, but found that too much of the rig's own radiated RF got picked up that way. The Rx mixer is followed by a IF stage featuring an NE592. The mixer's balanced output is directly connected to the amplifier's differential input, minimizing component count at this point. I got a sufficiently narrow bandpass action for the selection of the intermediate frequency using a single 4194 kHz crystal as the only Z element. Product detector and AF amplifier The second mixer operates as a product detector. It is followed by a NE592-based selective audio amplifier. The RF portion of the mixer's output signal is surpressed by the two capacitors C10/C11. The remaining AF signal is directly fed into the differential input of the NE592. The AF stage's frequency response is determined by the series resonant circuit DR1/C12. The stage has a gain of 42 dB at a measured center frequency 660 Hz. The volume adjustment takes place with the RF attenuator P1 close to the antenna input. Headphones with an impedance of at least 1 kOhm are mandatory here, due to the relatively high output impedance of the NE592. A LM386 is actually the preferential component for driving headphones, or a 8 ohms loudspeaker. But I wanted to try...

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