JPS5928557Y2 - tape recorder with radio receiver - Google Patents

Description

[Detailed description of the invention] A tape recorder with a radio receiver is often said to record broadcast waves while listening to them.

In this case, if an AC bias method is used as the tape recording bias method, the bias frequency is selected to be a high frequency of about 50-100 kHz, which is unrelated to the recording band, so harmonics of this bias signal and broadcast signals may cause a beat.

Therefore, conventionally, when a beat occurs, for example, the frequency of the bias signal is slightly changed to prevent the beat from occurring due to harmonic components of the bias signal.

In this method, beat interference can be removed by operating a frequency change switch when a beat occurs, but this method does not provide satisfactory results over a wide range of broadcast bands.

Problems arise particularly in broadcast bands where beats occur due to lower harmonics of the bias signal.

For example, in Europe, L
Due to the use of the W band as a broadcast wave band, the current
If you select kHz as the bias frequency, the third or fourth order
Beats are generated by extremely low-order harmonic components such as:

In this case, compared to the harmonic components that would cause the beat,
If the input electric field strength of the broadcast wave is much larger, for example, if the level difference is 50 dB or more, even if a beat occurs, it will not cause much of an audible problem.

However, tape recorders with built-in radio receivers use a bias oscillator and built-in antenna (such as a bar antenna).
are placed relatively close to each other,
The electric field strength of the harmonic component of the bias signal described above as an unnecessary opening received by this built-in antenna is relatively large.

Therefore, it is almost impossible to input the signal at a level that is audibly negligible.

Therefore, to remove beats in such cases,
It is necessary to move the harmonic components of this bias signal out of the band where beats occur by changing the bias frequency by a large amount, for example, about 10 kHz.

However, to vary the bias frequency over a wide range in this way, the circuit configuration becomes complicated and expensive.

Furthermore, changing the bias frequency by a wide range deviates from the optimal recording bias conditions, which also has the disadvantage that optimal recording cannot be achieved.

Although the explanation so far has mainly been about the state of beats in the LW band, it goes without saying that beats that cannot be easily removed as described above also occur in the MW band in Japan.

Taking these points into consideration, the present invention has been designed to simplify the configuration and completely and reliably remove the beats even when receiving and recording broadcast waves in any broadcast band. In the present invention, when a beat occurs, the harmonic of the bias signal is not separated from the frequency of the broadcast wave as in the past, but on the contrary, the frequency of this harmonic is made to match the frequency of the broadcast wave, resulting in a zero beat. It is configured as follows.

FIG. 1 is a basic and schematic system diagram of a tape recorder according to the present invention, in which 1 is a radio receiver, 2 is a receiving circuit thereof, 3 is an antenna, and 4 is a speaker.

Also, in close proximity to this radio receiver 1, a bias oscillator 5 is installed.
will be arranged.

6 is a magnetic head, T is an input terminal for a signal to be recorded, and in this example, a detected desired broadcast wave is supplied to this input terminal.

In this invention, we focus on the fact that the inter-office frequency (channel spacing) of broadcast waves is unified, and in order to achieve zero beat, the oscillation frequency of the bias oscillator 5, that is, the bias frequency fB, is the inter-office frequency of the broadcast waves. When fc is fB, fB-nf (3...
...... (1) (where n is an integer).

Here, the inter-office frequency fc in the MW band is 10 kHz in Japan.

Therefore, the bias frequency fB is 10 n (kHz)
become.

In order to satisfy the optimal bias condition, it differs depending on the type of tape recorder, but for example, n=s
That is, the bias frequency fB may be selected to be approximately 80 kHz.

□Since this bias frequency fB needs to be fixed without fluctuation under normal conditions, it is a matter of course to use a stable oscillation element such as a crystal as the bias oscillator 5.

In this way, if the via input frequency fB is selected to be an integral multiple of the inter-station frequency fc, the m-th harmonic component sB (m is a positive integer of 2 or more) will always be affected by any broadcast wave SA, as shown in Figure 2. Since both frequencies are the same, there is always a zero beat.

Here, let us consider again the electric field strengths of the broadcast wave SA and the bias signal.

Normally, broadcast wave SA is 6 times within its service area.
0 dB or more, whereas the signal strength of the bias signal arriving at the antenna 3 is about 40 ctB at maximum.

By the way, the present applicant has confirmed through various experiments that when there is a zero beat, if the difference in the level of two signals provided for the beat is 6 dB or more, especially 12 dB or more, there is no problem with hearing.

Therefore, as mentioned above, if the difference between the broadcast wave SA and the harmonic component SB is at least 20 ctB or more, the zero beat has no effect at all.

As explained above, in the present invention, the bias oscillator 5 is provided with a bias frequency rB selected such that the received broadcast wave and the harmonic component of the bias signal match (ie, zero beat).

In this way, no matter what broadcast wave is received, there will always be a zero beat, so there will be no beat interference, and good recording can always be achieved.

Furthermore, since the circuit configuration for taking the zero beat is extremely simple, this type of tape recorder can be provided at low cost, and since the zero beat can be taken automatically, there is no need for troublesome operations such as beat removal operations. It has the effect of wiping out operations.

FIG. 3 shows another example of the invention.

In the figure, 11 is a mixer, 12 is an IP circuit, and 13 is a detector (including a low frequency amplification system).

In this example, a reference oscillator 15 is provided, and the local oscillation frequency fQ and bias frequency fB of the receiver 1 are formed from this reference oscillation frequency fs.

Therefore, the reference oscillation frequency fs is selected to be an integral multiple of the inter-office frequency fc, and therefore a variable step-down circuit whose frequency variable interval is fc is provided as the local oscillation circuit 16, and an oscillation output is supplied thereto.

The reference oscillation frequency f3 (=mfc: m is an integer) is 1/l (
(l is an integer), a local oscillation frequency of -fQ is obtained.

In order to vary the local oscillation frequency fQ for each fQ, it is sufficient to make it related to the broadcast wave channel selection operation in which the inter-office frequency fc is unified.

On the other hand, the tape recorder side is provided with a frequency down-converter circuit which acts as a bias oscillator 5, and this frequency down-converter circuit 5 is also supplied with the oscillation output of the reference oscillator 15 mentioned above.

The output of the frequency down-converting circuit 5, that is, the frequency fB of the bias signal, is selected to be an integer multiple of the inter-office frequency fc, as described above, and therefore, the reference oscillation frequency fs is stepped down as desired to satisfy this condition. It is something that

In this way, the reference oscillator 15 is provided and each frequency fo
, fB can produce the same effect as described above.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of the main parts showing an example of a tape recorder with a radio receiver according to the present invention, Fig. 2 is a diagram of a zero beat used to explain its operation, and Fig. 3 is a diagram showing another example of the present invention. 1
This is a system diagram similar to that shown in the figure. 1 is a radio receiver, 5 is a bias oscillator, 6 is a magnetic head, 15 is a reference oscillator, SA is a broadcast signal, and SB is a bias signal.

Claims (1)

[Scope of utility model registration request] In a tape recorder equipped with a built-in radio receiver that receives broadcast waves with unified inter-office frequencies, the frequency of the AC bias signal is adjusted so that the received broadcast waves match the frequencies of the harmonics of the AC bias signal. Selected tape recorder with radio receiver.