RF-AMP Documentation

Posted on Feb 7, 2014

The amplifier can be used in a number of projects to buffer and amplify outputs from devices such as Direct Digital Synthesizer (DDS) chips. The board was initially produced to amplify the output of the 9833 DDS chip. The board was also intended for Amateur Radio applications (e. g. , a buffer amplifier for a VFO). Photo 1 shows the bare board and a

RF-AMP Documentation
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board populated with all components except the optional output filter network. The board shown uses a bifilar wound 4:1 output transformer (as shown on the schematic and mentioned below). Schematic 1 shows the RF-Amp circuitry and a typical configuration of the optional output network. Note: with the given filter network, frequencies above 10 MHz are greatly attenuated. The schematic shows the board`s component layout, circuitry and connection points. The amplifier provides a voltage gain of approximately 16 to 18 dB. Photo 2 shows a gain vs. frequency plot of the basic amplifier board with an output optimized for the 3-10 MHz range (2000 Ohm load). Shown on this plot are the results for three different transformer windings, as follows: Photo 3 shows a gain vs. load plot of the basic amplifier board for the three windings given above. These plots show that the output impedance of the amplifier is approximately 220 Ohms without the 4:1 winding. With the impedance transformer, the output impedance is reduced to approximately 150 Ohms. The reduction over the 12 turn transformer is not 4:1 probably because the differences between the collector impedances for the two different transformers; the collector loading for the two transformers is comparable, but not exact. With the 4:1 transformer, a 2000 Ohm load and a frequency of 6 MHz, the voltage ratio between the collector and secondary of the transformer was (4220 mV rms)/(2210...

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