Kenwood TS-890S, Подробное руководство

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RECEPTION CIRCUIT 02
First Mixer
For the first mixer, the “H-mode mixer” with less distortion is refined and diverted from the one adapted in the TS-990S
main receiver, and the conversion loss has been reduced and matching of the frequency characteristics of the mixer
input port by the wide bandwidth is enabled.
Fig. 3 First Mixer Circuit
Roofing Filters
What is a Roofing Filter?
This section describes the roofing filter, which is the most important in the receiver. The roofing filter is a filter placed
at the ceiling, or the “roof” of the intermediate frequency (IF) circuit of the receiver. In other words, this represents a
narrowband filter where the signal converted to the intermediate frequency first passes through. The received signals
include a number of strong adjacent interfering signals other than the desired signal, thus by the attenuated amount
outside the band of the filter, the signal is less likely to be distorted in the subsequent amplifying circuit. The high
intercept point obtained by the high-performance first mixer gives full play to its ability in a frequency domain slightly
distant from the desired signal, which is attenuated by the roofing filter. This is why the roofing filters have been narrowed
to their minimum and have been attenuated to the steepest direction.