JPS6128429Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a variable bandwidth circuit for an SSB receiver, and the object thereof is to provide a circuit that can minimize the number of required filters.

The relationship between the sideband and carrier frequency in the intermediate frequency amplification stage of an SSB receiver is generally divided into two types: one carrier frequency, an upper sideband filter, a lower sideband filter, and one carrier frequency. There are two types of filters: the USB carrier is placed at the 15-20 dB attenuation point on the low-frequency side slope of the filter, and the LSB carrier is placed at the 15-20 dB attenuation point on the high-frequency side slope of the filter.

Now, if you want to switch between filters with different bandwidths to create a two-stage variable bandwidth of wide band and narrow band, in the single carrier format described above, you need to switch between two filters each for USB and LSB.
Since four filters are required, a total of four filters are required. Furthermore, in the two-carrier format, one filter can be shared, so a total of three filters are required.

In a receiver, the filter is an important component that determines the selectivity, and therefore it is also among the most expensive components, so increasing or decreasing one filter is also important.In the method of the present invention, two filters are used to achieve the above-mentioned effect. It has the advantage of producing the same or better effects.

FIG. 1 shows the configuration of a filter circuit according to the present invention, and FIG. 2 shows the characteristics of the filter used therein.

In FIG. 1, a USB filter 1 and an LSB filter 2 in the intermediate frequency amplification stage are connected in cascade, and switch circuits 3 and 4 are provided to bypass unnecessary filter signals as necessary. The USB filter and LSB filter may be arranged one after the other, and a buffer or amplification stage may be added as necessary. The characteristics of this filter are as shown in Figure 2.For USB, the USB carrier is connected to the low frequency side slope of the filter with a high center frequency, and for LSB, the LSB is connected to the high frequency side slope of the filter with a low center frequency.
When using USB, use a USB filter and USB carrier, and use the LSB
Sometimes an LSB filter and LSB carrier are used, so the receiving bandwidth is the same as the bandwidth of the filter used.

Next, when both filters are used in cascade, the total bandwidth is only the portion where the bands of both filters overlap, so the bandwidth is narrowed by the difference between the center frequencies of both filters. At this time, the frequency of the filter is shifted so that the bands overlap on the side of the slope where the carrier is located, so the characteristics hardly change, and only the slope on the other side is shaved, resulting in a narrower bandwidth and the difference between adjacent signals. It is effective in removing interference and high-frequency components of noise that are easily perceived by the ears. Furthermore, when the band is narrowed in this way, the attenuation characteristics of both filters overlap, so the amount of out-of-band attenuation increases additively, making it even more effective in eliminating interference, which is the objective of the narrow band.

Conventional variable band circuits using filters have been constructed by switching a large number of filters or by superimposing filter characteristics between multiple intermediate frequency stages of multiple conversion. The circuit of the present invention has the advantage of being able to commercialize relatively inexpensive and popular products, which have not been readily available due to technical difficulties associated with conversion and conversion, at a cost not much different from that of adding one filter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of this devised circuit, and FIG. 2 is an explanatory diagram showing the filter characteristics and the principle of variable bandwidth. 1, 2...filter, 3, 4...switch circuit.

Claims (1)

[Scope of utility model registration request] In the intermediate frequency amplification stage of the SSB receiver, two filters with approximately equal bandwidth are connected in cascade, and each filter has a slope on the low frequency side of the filter with a high center frequency for USB.
The USB carrier is configured by setting an LSB carrier on the high frequency side of a filter with a low center frequency, and the center frequency difference between the two filters is set to be approximately equal to the frequency at which the bandwidth is desired to be reduced. A bandwidth switching circuit that uses a carrier and a filter for unnecessary sidebands, bypasses the signal, and uses both filters in cascade during narrowband reception to operate the carrier of the required sideband.