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Poor man SWR Analyser

Poor man SWR Analyser

A SWR analyser for frequency range 2.9 – 16.0 MHz (Lo) and 12.0 – 39.0 MHz (Hi).
A CMOS VCO excites an RF bridge. In the bridge, the antenna under test is compared to a 50 ohms resistor. The bridge unbalance is displayed on a meter with SWR scale.

Due to the square wave used to excite the bridge, the VSWR can only be considered a rough indication. Due to the harmonics of the square wave, the indicated SWR is probably above the ‘real’ SWR when measuring antennas – especially at the low end of the band (80 meter).

The analyser has an output for a Frequency counter. The VCO potentiometer can be equipped with a scale to indicate frequency. Power source is a 9 Volt alkaline battery. Voltage is stabilized at 5 Volt for the logic circuit using an LM78L05

A VCO from the 74HCT4046 PLL integrated circuit outputs a square wave. This output is routed through a buffer (74HC00) to an output for a Frequency Counter (BNC) and a 50 Ohm RF bridge.

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