JP3253897B2 - FM transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an FM transmitter used for a wireless microphone or the like, and more particularly to an FM transmitter which can omit a PLL synthesizer.

[0002]

2. Description of the Related Art An FM transmitter mounted on a wireless microphone or the like transmits at a frequency in an FM broadcast band, and an unlicensed transmission output has a field strength of 3 m.
It is determined to be 0 μV / m or less, and less than 250 μV / m in the United States.

FIG. 6 is a block diagram of a conventional FM transmitter 48. The same parts as those of the embodiments of the invention described later are designated by the same reference numerals, and the description thereof will be omitted. In the PLL synthesizer 50, the oscillator 54
Generates a sine wave corresponding to the oscillation frequency fr of the vibrator 52, and the R frequency divider 56 and the S frequency divider 58 set the output frequencies of the oscillator 54 and the VCO (voltage controlled oscillator) 12 to 1 / R,
The frequency is divided to 1 / S (R and S are both natural numbers) and output to the frequency / phase comparator 60. L. P. F (low-pass filter) 62
Pass only the low-frequency component of the output of the frequency phase comparator 60, and the adder 64 P. The output of F62 is added and output to VCO12. The output of the VCO 12 is also output to the amplifier 26 together with the S divider 58,
At, the FMRF is transmitted. The four switches in the switch row 68 correspond to the four S's in the S divider 58, and the user selects one switch in the switch row 68 and turns it on to select S. You. The microcomputer 66 detects which switch in the switch row 68 has been selected,
A corresponding control signal is sent to the PLL synthesizer 50.

The output frequency of the VCO 12 changes and the VCO 12 changes so that the output frequency from the S divider 58 to the frequency phase comparator 60 matches the output frequency from the R divider 56 to the frequency phase comparator 60. Output frequency slightly changes due to a minute voltage change component of the audio signal, so that the FM signal of the audio signal is generated at the output terminal of the VCO 12. Further, the following relationship is established between f1 and fr by the closed loop of the VCO 12 and the frequency phase comparator 60. f1 = (S / R) · fr

[0005]

SUMMARY OF THE INVENTION FM transmitter 48
The problems are as follows. (A) Since the transmission frequency is stabilized by the PLL synthesizer 50, it is difficult to generate a low-frequency FM. (B) The user selects one of the four switches in the switch row
It is necessary to select an individual and operate it, which is complicated. (C) An expensive PLL synthesizer 50 is required. (D) Since the VCO 12 is more vulnerable to disturbance as the input frequency deviates from the free-running frequency, the transmission frequency is limited to switching within a range of about 2 MHz.

It is an object of the present invention to provide an FM transmitter which overcomes the above-mentioned problems.

[0007]

The FM transmitter (10) of the present invention has the following (a) to (c). (A) VCO (12) that generates an FM signal using an audio signal as a modulation signal (b) Amplitude modulation wave generator (20, 22) that generates an amplitude modulation signal using the output of VCO (12) as a modulation signal ) Transmitter (28) for transmitting the output of the amplitude modulated wave generator (20, 22)

[0008] Since the FM signal of the audio signal is generated by the VCO (12), and further, the FM signal is amplitude-modulated and transmitted, the FM signal of the audio signal has a different band between the upper band and the lower band. Will be sent. This FM transmitter (10) omits a PLL synthesizer and saves the user the trouble of switching transmission frequencies one by one.

According to the FM transmitter (10) of the present invention, the VCO (12) and the amplitude modulation wave generator (20, 22) as a whole
A total of four FM signals having different frequency bands can be generated.

According to the FM transmitter (10) of the present invention, a total of four frequency bands having different frequency bands are set so that at least one of the frequency bands does not overlap with a frequency band of an FM broadcasting station in an arbitrary region. Have been.

[0011] For example, the station of FM broadcasting is 400 in the United States.
Since this is a KHz span, this 400 KHz span is set by setting the interval fc between the upper and lower sidebands and appropriately setting the frequency of the amplitude-modulated carrier.
At least one of the four frequency bands secured as the frequency band of the FM signal transmitted by the FM transmitter (10) can be made not to overlap with the band of the FM broadcasting station in an arbitrary area.

According to the FM transmitter (10) of the present invention, a total of four FM signals having different frequency bands are generated by the amplitude modulation wave generator (20, 22) based on each of the two carrier waves having different frequencies. By generating an upper band wave and a lower band wave.

According to the FM transmitter (10) of the present invention, two carrier waves having different frequencies are supplied to the common oscillator (14).
Is obtained by frequency multiplication based on two multipliers (16, 18) having different multiplication numbers.

By using the multipliers (16, 18) to generate two carriers having different frequencies, the number of oscillators (14) can be reduced.

According to the FM transmitter (10) of the present invention, two carrier waves having different frequencies are generated by the oscillator (14) having two oscillation frequencies.

According to the FM transmitter (10) of the present invention, a total of four FM signals having different frequency bands are connected to the VCO (1).
It is obtained by generating two FM signals having different frequencies by switching the two free-running frequencies in 2), and generating an upper band and a lower band for each FM signal in the amplitude modulated wave signal.

According to the FM transmitter (10) of the present invention, the VCO (12) receives an audio stereo composite signal.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows an FM transmitter 10
It is a block diagram of. The FM transmitter 10 is provided in, for example, a wireless microphone. The VCO 12 receives the audio signal and outputs a frequency corresponding to the amplitude of the audio signal, that is, an FM signal of the audio signal. The crystal oscillator 14 generates a sine wave having a frequency fr. The N multiplier 16 and the (N + M) multiplier 18 generate a sine wave having a frequency obtained by converting the frequency of the crystal oscillator 14 into N and (N + M) times, respectively. The mixer 20 performs double-sideband modulation (DSB) on the sine wave from the N multiplier 16 with the modulation signal from the VCO 12. Similarly, mixer 22 includes (N
+ M) The sine wave from the multiplier 18 is double-sideband modulated by the modulation signal from the VCO 12. The outputs of the mixers 20 and 22 are added in an adder 24, amplified in an amplifier 26, and then transmitted as an FMRF signal from a transmission unit 28.

FIG. 2 shows the FM transmitted from the transmitting unit 28 in FIG.
FIG. 3 is a frequency spectrum diagram of an RF signal. However, the specifications are set as follows. N = 6, M = 1, fr = 1
2.8 MHz, fc = 0.3 MHz.

A method of determining the values of each item will be described. F
It is assumed that the low edge of the M broadcast band is fl and the high edge is fh. Conditions for outputting four waves from fl to fh are as follows in relation to the low edge side and the high edge side, respectively (1)
Equation (2) is obtained. N · fr−fc ≧ fl (1) (N + M) · fr + fc ≦ fh (2) Therefore, the following equation (3) is established. Where N, f
r, fc, fl, fh are all positive. (Fr + fc) / N ≦ fr ≦ (fh−fc) / (N + M) (3) where M = 1, fc = 300 Khz, fl = 87.5.
Assuming that MHz and fh = 108 MHz, the following equation (4) is established. FIG. 2 shows the FM broadcast band in Japan, but fl = 87.5 MHz and fh = 108 MHz correspond to the FM broadcast band in the United States. N ≧ 1 / ｛(fh−fc) / (fl + fc) −1｝ ≒ 4.41 (4) ∴N ≧ 5 (∵N is a natural number) When N = 5 and M = 1, fr is Range. 17.56 MHz ≦ fr ≦ 17.95 MHz (5) は fr is 17.6, 17.7, 17.8, 17.9 MH
z. If fr = 17.8 MHz is selected, the transmission frequency is 88.7, 89.3, 106.5, 107.1 M
Hz. In the United States, there are always places where there are no FM broadcasts with these four waves because the local stations have a 400 KHz span.

FIG. 3 is a block diagram of the FM transmitter 10 capable of transmitting a stereo signal. L and R
The audio signal of the channel is converted into a stereo composite signal in the stereo composite signal generator 30 and output to the VCO 12 as a modulation signal. In the FM transmitter 10, an adder 24 is provided in a stage preceding the mixer 20, adds the outputs of the N multiplier 16 and the (N + M) multiplier 18, and sends the sum to the mixer 20. Therefore, the mixer 22 of FIG. 1 is omitted. In the mixer 20, both carrier waves from the N-multiplier 16 and the (N + M) -multiplier 18 are subjected to double-sideband modulation using the FM signal from the VCO 12 as a modulation signal, and for example, a total of four FMRF signals as shown in FIG. Generated.

FIG. 4 is a block diagram of an FM transmitter 10 equipped with a crystal oscillator 14 for manually switching the oscillation frequency. The crystal oscillator 14 has an oscillation frequency fr
A crystal oscillator 32 and a crystal oscillator 34 of 1 and fr2 are provided, and the user selects one of the switch 36 and the switch 38 and turns it on to switch the oscillation frequency of the crystal oscillator 14 to fr1 or fr2. It has become. In the FM transmitter 10, the (N + M) multiplier 18 shown in FIG.
And the adder 24 are omitted. In the FM transmitter 10 of FIG. 3, four FMRF signals are transmitted simultaneously, whereas in the FM transmitter 10 of FIG. 4, two FMRF signals are transmitted simultaneously.

FIG. 5 is a block diagram of still another FM transmitter 10. In this FM transmitter 10, V
If the free-running frequency of CO12 is fc1 or fc2 (fc1 <fc
It can be switched to 2). Also, crystal oscillator
The oscillation frequency of 14 is only one of fr. In the case of fc2, fc1 and fc2 are set so that the sidebands above and below the DSB of the FMRF signal generated by the mixer 20 are higher and lower than the case of fc1.

[Brief description of the drawings]

FIG. 1 is a block diagram of an FM transmitter.

FIG. 2 is a frequency spectrum diagram of an FMRF signal transmitted from a transmission unit in FIG. 1;

FIG. 3 is a block diagram of an FM transmitter capable of transmitting a stereo signal.

FIG. 4 is a block diagram of an FM transmitter equipped with a crystal oscillator that switches the oscillation frequency manually.

FIG. 5 is a block diagram of still another FM transmitter.

FIG. 6 is a block diagram of a conventional FM transmitter.

[Explanation of symbols]

 Reference Signs List 10 FM transmitter 12 VCO 14 Oscillator 16 N multiplier (multiplier) 18 (N + M) multiplier (multiplier) 20, 22 Mixer (amplitude modulated wave generator) 28 transmitter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03C 3/06 H04B 1/034 H04B 1/04 H04N 5/40

Claims (8)

(57) [Claims] 1. A VCO (12) for generating an FM signal using an audio signal as a modulation signal, and (b) the VCO (12).
An amplitude-modulated wave generator (20, 22) that generates an amplitude-modulated wave signal using the output of (a) as a modulation signal, and (c) a transmission unit (28) that transmits an output of the amplitude-modulated wave generator (20, 22). An FM transmitter, comprising: 2. The VCO (12) and the amplitude modulation wave generator (20, 22) as a whole can generate a total of four FM signals having different frequency bands. The FM transmitter as described. 3. A total of four frequency bands having different frequency bands are set so that at least one of them does not overlap with a frequency band of an FM broadcasting station in an arbitrary area. Item 3. The FM transmitter according to Item 2. 4. A total of four FM signals having different frequency bands, the amplitude modulated wave generator (20, 22) outputs an upper band wave and a lower band wave based on each of two carrier waves having different frequencies. The FM transmitter according to claim 2, wherein the FM transmitter is obtained by generating 5. The two carrier waves having different frequencies are used to output the output of a common oscillator (14) to two multipliers having different multiplication numbers.
The FM transmitter according to claim 4, wherein the frequency is multiplied based on (16, 18). 6. The two carriers having different frequencies are 2
5. The FM transmitter according to claim 4, wherein the FM transmitter is generated by an oscillator having a plurality of oscillation frequencies. 7. A total of four FM signals having different frequency bands are generated by switching two free-running frequencies in said VCO (12) to generate two FM signals having different frequencies and said amplitude-modulated wave signal. 4. The FM transmitter according to claim 2, wherein the FM transmitter is obtained by generating an upper sideband and a lower sideband with respect to each FM signal. 8. The FM transmitter according to claim 1, wherein the VCO (12) receives an audio stereo composite signal.