Preamplifier for RF Sweep Generator
Preamplifier for RF Sweep Generator Circuit diagram. The RF sweep frequency generator (‘wobbu-lator’) published in the October 2008 issue of Elektor has a receiver option that allows the instrument to be used as a direct conversion receiver. This receiver does however have a noise floor of only –80 dBm, which really should have been –-107 dBm to obtain a sensitivity of 1 µV. So, for a good receiver sommore gain is required. A wideband amplifie however, generates a lot of additional noisas well and as a consequence will not resuin much of an improvement. As an experiment, the author developed a selective receiver with a bandwidth of about 4 MHz. Because a gain of at least 35 dB is required, the preamplifier consists of two amplifying elements. The input amplifier is designed around a dual gate MOSFET, type BF982. This component produces relatively little noise but pro-vides a lot of gain. The output stage uses a BFR91A for some additional gain. Preamplifiers where both the ga...