Column: Circuit drill
Power supplies for optimum continuous- wave filter performance
By Dr. Sulaiman Algharbi Alsayed, Managing Director, Smart PCB Solutions
modulation, where a carrier wave is turned on and off to convey information. Tis communication is commonly associated with the Morse code, where short and long intervals of the carrier wave represent dots and dashes, respectively. A CW filter is specifically designed to
A
isolate and enhance RF signals, oſten used in radio receivers to improve selectivity and isolate the desired signal from noise and interference. Tis filter’s primary purpose is to pass signals within a
continuous wave (CW) filter is one of the important circuits in the design of radio communication systems. CW is a type of
narrow frequency range around the carrier frequency of the desired signal whilst attenuating signals outside that range. Tis helps improve the received signal’s signal-to- noise ratio, with reduced interference from other signals.
A typical CW filter circuit A typical CW filter consists of four filtration stages using two dual op-amp circuits; see Figure 1. Te filter has two power supplies, V3 and V2, with V2 powering all four op- amps, and V3 is a boosting power supply, 6-8Vdc. My question is: What’s the optimum voltage for both V2 and V3 to obtain the highest output signal? Figure 2 shows the frequency
performance of the CW filter of Figure 1.
It has a very narrow bandpass range, to allow the received carrier frequency and suppress other frequencies; the bandpass is set at 20MHz.
Experiment methodology For the experiment I took into consideration the operating voltage of the op-amp, UA747, which is 5-18Vdc. Te circuit was fed this DC voltage range at 1Vdc increments. For simplicity and to make sure I cover a wide practical range, the V2 power supply was set at 1-18Vdc, with incremental voltages of 1Vdc. Te maximum output signals were logged
at each V2 and V3 voltage level. A function generator supplied sweeping input signals with frequencies starting from 1MHz to
Figure 1: A typical CW filter circuit
08 June 2024
www.electronicsworld.co.uk
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