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 50Ù 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.
http://pe2er.nl/PoorMansSWRanalyser/index.htm
