STAR LO Buffer Amplifier

The PICASTAR uses a single transistor stage to buffer the DDS Reconstruction Filter and feed the required signal level to the 'Magic Roundabout' (MR).

In this section will eventually be an analysis of the amplifier, particularly with a view to achieving an input impedance much greater than the original 20R or so, to determine whether it is possible to reach a reliable figure of 200R for more directly terminating the original reconstruction filter and avoiding the signal loss in the original terminating and matching resistor.

If successful, this could be an alternative to the reduction to 50R of the filter impedance. However, the original filter characteristic, with reducing attenuation of DDS image frequencies, would not change. Since those who are likely to be in a position to re-work LO components can just as easily change the filter impedance, they may as well build the 50R filter and kill two birds with one filter.

The PICASTAR buffer amplifier is a clone of the design which originally appeared in QST of November 1981, Hayward & Lawson's "Progressive Communications Receiver", with identical topology and component values.

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