Local oscillator for KB transceiver. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Local oscillator for KB transceiver. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes

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At present, equipment made according to a double frequency conversion scheme with a fixed first IF is gaining more and more popularity among shortwaves. Such a construction of a transceiver or receiver has a number of advantages. However, in this case, there are some difficulties in creating a highly stable smooth range generator (the first local oscillator). Good results here can be obtained using a premixed local oscillator, but such a local oscillator is rather complicated. In addition, it requires the use of scarce quartz resonators (up to 5 - 7 resonators to completely cover all amateur KB bands).

Local oscillator for KB transceiver

Achieving good stability in a simpler oscillator-switched LO is difficult due to the need to vary the oscillator output frequency over a wide range (with the most common 9 MHz first IF being 5,5 to 21 MHz!).

However, these limits are significantly narrowed if frequency multiplication is applied to the local oscillator. In this case, it is possible, by optimizing the operation of a smooth generator, to achieve its high stability, close to the stability of an unswitched generator for the same frequency range. The functional diagram of such a local oscillator is shown in the figure. It consists of a smoothly switched oscillator G1, a buffer amplifier U1, a multiplier U2 and band pass filters U3.

For the first intermediate frequency of 9 MHz, the frequency of the generator G1 must lie within 5 ... 6,9 MHz. The values of the operating frequencies of the smooth generator and the numbers of harmonics allocated in the frequency multiplier for various amateur bands are given in the table.

Local oscillator for KB transceiver. Table

Literature

CQ (USA), 1978. No. 7

Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Knots of amateur radio equipment. Generators, heterodynes.

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