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Sensitivity and selectivity are the major concerns of a short wave enthusiast when he looks up for a receiver. Commercial communications models with superhet circuitry surely satisfy his requirements, but these are expensive. He would rather go for a homebrewed radio, being a regenerative receiver an affordable choice. I'm also a short wave listener and for some time I used my family's MW and SW tube radio, Philips brand. Then I switched to a Sony ICF-7600 with ceramic filters in the IF stages. High selectivity was attained with this radio receiver.

This circuit is for a QRP (low power) antenna tuner, a.k.a. a transmatch, for use in the short wave amateur radio bands from 3-30 Mhz. It allows a wide variety of antennas to be connected to a low power transmitter. When the circuit is properly tuned, the maximum transmitter power will be delivered to the antenna. It is used in conjunction with a standing wave ratio (SWR) meter. This is a fairly generic antenna tuner circuit.

SWR can be adjusted by adjusting the connection point L3 figher or lower.

A much better type of antenna then a simple quatre wave and that has more gain is the 1/2 wavelength vertical. We know that the impedance of the 1/2 dipole is 70 Ohms when we attach the coax in the middle, but what if we were to attach our coax directly to the end? The impedance at this point is high, very high, so we must make a matching device to match the antennas impedance to the 50 Ohm coax. What would happen if we did not use this matching device? Well...you would know that this would result in a very very high SWR.

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1. Full 5 watt output using a power MOSFET final that is resistant to high SWR and thermal runaway. This final is very efficient and runs much cooler than traditional bipolar designs. 2. Highly sensitive and selective superhetrodyne receiver with plenty of audio to drive a speaker. About 100 Khz of tuning range is provided through a varactor diode along with a switchable RIT control. 3. Full break-in keying with a unique T/R switching system. Work is continuing on a printed circuit board and this circuit is expected to be available as a complete kit including all electronic parts, PCB and instruction manual at a future date. My prototype was built on Radio Shack universal boards.

The antenna tunning circuit can accommodate 1/2 wave length antennas or higher, for input resistances of 50 Ohms which make it suitable for CB (Citizen Band) transceivers. C1 is for fine tunning and C2 is just for tunning. Turning C3 with the help of C2 you can set the SWR to 1:1. The Coil L is made of 11 turns of insulated copper wire with diameter of 1mm.

This circuit is for a QRP (low power) antenna tuner, a.k.a. a transmatch, for use in the short wave amateur radio bands from 3-30 Mhz. It allows a wide variety of antennas to be connected to a low power transmitter. When the circuit is properly tuned, the maximum transmitter power will be delivered to the antenna. It is used in conjunction with a standing wave ratio (SWR) meter. This is a fairly generic antenna tuner circuit.

This ultra-bright white LED lamp works on 230V AC with minimal power consumption. It can be used to illuminate VU meters, SWR meters, etc. Ultra-bright LEDs available in the market cost Rs 8 to 15. These LEDs emit a 1000-6000mCd bright white light like welding arc and work on 3 volts, 10 mA. Their maximum voltage is 3.6 volts and the current is 25 mA. Anti-static precautions should be taken when handling the LEDs. The LEDs in water-clear plastic package emit spotlight, while diffused type LEDs have a wide-angle radiation pattern. This circuit (Fig. 1) employs capacitive reactance for limiting the current flow through the LEDs on application of mains voltage to the circuit.

The circuit in Figure 1 uses an LM3914 LED driver to directly display standing-wave ratio (SWR) in a low-cost, rugged instrument. The SWR-sensing head is derived from the ARRL Antenna Handbookin an article that describes the tandem match. The forward voltage and reflected voltage (VF+VR ) signal drives Pin 6 (RHI ), and the VF–VR signal drives the normal signal input at Pin 5. You can use this basic arrangement to display the ratio of two voltages in other applications. The internal circuit of the LM3914 comprises 10 voltage comparators that compare the input voltage at Pin 5 to an internal, 10-step, linear-voltage-divider string between Pin 6 (RHI ) and Pin 4 (RLO ).

This is a successor of the PIC16C71 4-digit LED f-counter & V-meter. Some hard to find parts used in the previous version, which are out of production for some time, has been omitted. A rather early PIC16C71 has also been replaced by 28-pin device PIC16F876. The later is capable of driving 4 digit LED display in multiplexed mode while measuring frequency, power supply voltage as well as handle two analog inputs to display SWR/PWR signal strength in a bargraph manner. There is no need for external LED display driver chip as well as external data EEPROM since it is already implemented in PIC16F876.

This PCB VSWR bridge may be built on a length of double-sided PCB material (or two single-side boards sandwiched). One side of the PCB is not etched and the other side contains the RF directional couplers. All components are mounted flat on the board. The whole assembly can be built with a thickness of less than 5-mm. A good indication can be obtained from 1-watt at 144-MHz and 10-watts in the HF band. I do not know the maximum safe power, but it should certainly take 100-watts or more.

This is a successor of the PIC16C71 4-digit LED f-counter & V-meter. Some hard to find parts used in the previous version, which are out of production for some time, has been omitted. A rather early PIC16C71 has also been replaced by 28-pin device PIC16F876. The later is capable of driving 4 digit LED display in multiplexed mode while measuring frequency, power supply voltage as well as handle two analog inputs to display SWR/PWR signal strength in a bargraph manner.