The VFOs are switched in the receiver for the two bands when used with the Electroluminescent Receiver. The schematic in the Flying Pigs article showed Q4 also supporting the mute function for the receiver. The output circuit with the 2 RF chokes and single ended output allows a broadband output in the HF frequency range. Schematic of CDG Low pass filters: The circuitry near the top of the schematic Q5 shown above is the shaping circuit for keying the LM and and the shaping circuit Q4 for keying the oscillator. Instructions are simple and thorough.
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This compact and inexpensive SSB transceiver presented here is based on two MC integrated circuits. MC was developed by Motorola and released to the market in In the history of semiconductors there are very few integrated circuits that are still in production after more than 40 years from their initial release.
MC is one of them. You can buy MC from here. MC provides an external Carrier Null circuit, getting better carrier rejection than other similar circuits, where the balance is done inside of the chip.
This is an option for every builder, to what voltages have available. Because the MC is a transformer-less circuit Gilbert cell , theoretically this have no limit in low frequency characteristic as ring diode mixers which use transformers , and the useful working frequency can be practically down to the DC. The signal is passed further to the receive down-conversion mixer IC1 which is based on MC To get maximum conversion gain and sensitivity the external emitter resistance on the lower differential amplifier pair has been reduced to zero short between pin 2 and 3 of MC For 20m band, when using 4.
The Crystal Ladder Filter uses four identical 4. I have made this transceiver with different intermediate frequencies using crystals at 8. For amateur test conditions I found that the 4. The Intermediate Frequency placed on 4. High-side LO injection is necessary in the receiver to move up in frequency the image frequency, making easier its rejection.
The image frequency in our case is about 23 MHz, almost 9 MHz far from the receive frequency. Notice About Ladder Crystal Filters The measured bandwidth and out-of-band rejection of ladder crystal filters have a limit of using up to 6 crystals. Increasing more than 6 the number of crystals, the performances of the filter increase insignificantly.
This is a useful attribute when one is dependent upon surplus sources for the supply of crystals. This stage is used in both modes, RX and TX. Both potentiometers TX gain and RX gain , should be placed on the front panel of the transceiver, together with the audio volume potentiometer.
Pin 6 is for audio output, and pin 12 is for TX RF output. Operating with a high carrier level input maximize the device gain and insure that any amplitude variations present on the carrier do not appear on the output sidebands. It has the disadvantage of increasing some of the spurious signals and lower carrier rejection. Another benefit of the MC working as a Product Detector is its high sensitivity.
At frequency of 4. The gain of the mixer in those conditions is about 12dB, and the audio output level is enough to drive directly the TDA audio power amplifier. The total sensitivity of the receiver is better than 0. As a result of high sensitivity of the Product Detector, the gain of the receiver from antenna connector to the detector input, is not necessary to be very high, improving in this way the overall receiver linearity and noise floor.
The adjustment of this resistor is critical for various bias currents and Vcc voltages of MC The output of the TX RF mixer pin 12 of IC2 is relative high level, and using after the mixer only three amplifier stages you can get about 15W output power at the antenna connector. In this case, the total output power will be less than 10W. Tuning of the transceiver is relative simple. May start tuning the transmitter injecting an audio signal ideally dual-tones at the microphone input, and tune the following resonant circuits for maximum output power at antenna connector: TR2, TR3, and TX BPF.
Both TR2 and TR3 resonates on 4. For adjusting the carrier rejection need an oscilloscope probe placed before the Crystal Filter, and adjust for minimum carrier leakage from the "Carrier Null" variable resistor. The symmetry of the LO signal is important to get good carrier suppression.
The BFO frequency should be about 1. In CW mode the frequency of the BFO and the CW pitch is set by a group of capacitors placed in parallel with this trimmer capacitor using a switching diode circuit D2.
The frequency of the audio tone could be adjusted varying the 3. The audio power amplifier is based on TDA , circuit which was presented in earlier schematics as a good choice for a low distortion and low noise audio amplifier.
LM1496 DATASHEET PDF
PDF LM1496 Datasheet ( Hoja de datos )