Heterodyne transceiver for KB

Currently the official borders become increasingly popular instrument, is made under the scheme with double frequency conversion at a fixed first if. Such a construction of the transceiver or receiver has a number of advantages. However, in this case there are some difficulties in creating a highly stable generator of a smooth range (first local oscillator (lo). Good results can be obtained using heterodyne with premixing frequency, but this lo is quite complicated. In addition, it requires the use of scarce quartz resonators (up to 5 - 7 resonators for full coverage of all Amateur LW bands).

To achieve good stability in a simple oscillator with switchable generator is difficult because of the need to adjust the output frequency of the generator in a wide range (most common value of the first FC 9 MHz from 5.5 to 21 MHz!).

However, these limits are narrowed considerably, if applied to the local oscillator frequency multiplication. In this case, optimizing the work of the modulating oscillator to reach its high stability, close to stability is not switchable; generator to the same frequency range. Functional diagram of the oscillator shown in the figure. It consists of a smooth switching of the generator G1, a buffer amplifier U1, the multiplier U2 and band-pass filters U3.

For the first intermediate frequency 9 MHz frequency generator G1 must be in the range 5...to 6.9 MHz. The values of operating frequencies of the modulating oscillator and numbers of harmonics generated in the frequency multiplier for the various Amateur bands shown in the table.

Literature

CQ (USA), 1978. No. 7

Publication: N. Bolshakov, rf.atnn.ru