JPH04245814A - Fm transmission circuit - Google Patents

Abstract

PURPOSE:To equalize frequency stability in an FM mode to that in other modes in a multimode radio transmitter-receiver such as an amateure radio, etc., and to improve a modulation characteristic, and to eliminate its difference due to band. CONSTITUTION:In the multimode radio transmitter-receiver of a multiplex switching superheterodyne type, at the time of using the FM transmission mode, an FM signal F1 equal to a first intermediate frequency is generated by adding a modulation signal to the VCC 11 of a PLL oscillator 3 controlled by reference frequency fr based on second local oscillation frequency f2, and it is mixed with first local oscillation frequency f1 by a first mixer M1, and operation frequency F0 is transmitted.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] Applicable to transmitting/receiving wireless communication equipment that operates in a wide range of operating frequency bands and in many modulation modes, such as radio transceivers for amateur radio.

0002

[Prior Art] AM, CW, SSB, and FM are used in amateur radio communications in a wide frequency range such as the entire HF band.
A multi-conversion superheterodyne system, as illustrated in FIG. 3, is often used for communication devices operating in multiple modes such as the above.

[0003] The biggest reason for this is especially SSB (Singl.
3K required when receiving e Side Band) waves
Narrow bandwidth selectivity on the order of Hz and allowable frequency variation of 100 Hz
This is because a high degree of frequency stability of Hz or less can be obtained, and during transmission, the carrier wave and one sideband are removed from the AM wave while reversing the receiving path, and the SSB wave can be sent out. The outline of its configuration is described below.

FIG. 3A shows the configuration of a receiving circuit of a multiple conversion type transmitter/receiver, in which the received radio wave F0 is mixed with a first local oscillation frequency f1 in a first mixer M1 to produce a first intermediate frequency F1.
1, and is mixed with the second local oscillation frequency f2 in the second mixer M2 to become a second intermediate frequency, which becomes an audio signal in the demodulator DM, and operates the speaker SP via the low frequency amplifier AF.

[0005] At least 3 to 30 amateur radio equipment
MHz, the first intermediate frequency F1
By setting F2 to 30 MHz or more, image interference can be reduced, and by setting the second intermediate frequency F2 to a frequency suitable for a narrow band filter (for example, 455 kHz), sufficient interference removal characteristics can be obtained.

As for frequency stability, the first local oscillator is P
Sufficient performance can be obtained by using LL control, adjusting the frequency by making it variable, and controlling the second local oscillator by crystal control.

[0007] For SSB and CW reception, product detection is performed by injecting f3 from the carrier oscillator into the demodulator DM, and for AM and FM reception, the carrier oscillator is stopped and A
In M, demodulation is performed by amplitude detection, and in FM, demodulation is performed by a discriminator.

[0008] Adjacent selectivity mainly depends on the filter characteristics of the second intermediate frequency stage, and for AM, CW, and SSB, a filter with a passband width of about 3 kHz may be shared, but the optimum filter is determined separately. Width filters are often used. Since a bandwidth of 5 kHz or more to several tens of kHz and limiter characteristics are required for FM, the second intermediate frequency is usually demodulated with a discriminator through a separate limiter amplifier.

At the time of transmission, as shown in FIG. 3(B), at the time of SSB transmission, the output of the microphone amplifier MA is sent to the balanced modulator B.
By amplitude modulating the carrier f3 with M (which can be shared with DM during reception), a reduced carrier AM wave is obtained, so by moving the carrier frequency out of the band of the second intermediate frequency stage filter, unnecessary sideband and the carrier-suppressed SSB wave, which is sent to mixer M2 and mixer M.
1 and the operating frequency F0 by reverse frequency conversion to that during reception.
The received signal is amplified to the required transmission power by the power amplifier PA and sent to the antenna.

[0010] During AM transmission, AM waves are generated by re-adding an appropriate amount of carrier to the SSB signal, and CW
During transmission, the carrier is directly inserted into the intermediate frequency stage, and keying is performed at the intermediate amplification stage or PA stage.

[0011] Regarding FM transmission, since its use was added later to this type of transceiver, there is no necessity to perform multiplex conversion, and the following several methods are used for convenience. ing.

In FIG. 3, (1) adds the FM wave of the second intermediate frequency to M2 like the block FM1, and sends out the FM wave of the operating frequency F0 by performing frequency conversion inverse to reception. (2) is the FM of the first intermediate frequency like block FM2.
wave is added to M1, and an FM wave of operating frequency F0 is sent out by frequency conversion inverse to reception. (3) is a method of frequency modulating the second local oscillator in the CW transmission state as in block FM3, and adding the FM wave of the first intermediate frequency output from mixer M2 to mixer M1. In (4), the first local oscillator is frequency modulated in the CW transmission state as in block FM4, and the FM wave of the operating frequency F0 is added to the PA and sent out from the mixer M1.

[0013]

[Problem to be solved by the invention] As stated in the previous section,
Since the FM mode of the multiplex conversion radio transceiver is a function added for convenience, it is less necessary in the circuit configuration than other modes.

In the case of the block FM1 illustrated in the previous section,
There are difficulties in generating FM waves with a relatively large frequency deviation relative to a relatively low second intermediate frequency. Block FM
In case of No. 2, since the carrier frequency is higher than that of the previous example, there is less problem with the amount of frequency deviation, but it is necessary to separately provide a frequency modulator with high frequency stability. Block FM3 is the second
The local oscillator is converted into a VCO (Voltage Control).
Since the FM wave is generated by adding an audio signal to this as an oscillator, there are few changes to the circuit configuration, but it is possible to replace the VCO with a VC with good frequency stability.
XO (Voltage Controlled X
tal Oscillator), it cannot be denied that the stability is lower than that of a fixed frequency XO. In block FM4, an audio signal is added to the PLL circuit of the first local oscillator to generate an FM wave, so although it cannot be generalized depending on the configuration of the PLL circuit, generally speaking, the first local oscillator circuit, which has a complicated configuration, is Side effects of adding functionality must be considered.

Since each of the four types of FM transmitting circuits described above has its own problems, there is a need for a further improved FM transmitting circuit.

[0016]

[Means for Solving the Problems] In the present invention for solving the above-mentioned problems, as shown in FIG. PLL control oscillation circuit 1 that generates
will be established. The PLL control oscillation circuit 1 may have a standard configuration, and includes a VCO 11 that oscillates at a frequency F1', a frequency divider 12 that divides the oscillation frequency F1', and a phase comparison of the divided frequency with a reference frequency fr. The oscillation frequency of the VCO is stabilized by adding this phase difference component to the VCO 11 as a DC control voltage Vc through the LPF 14 and the phase detector 13 which outputs a phase difference component. This oscillation frequency stability mainly depends on the stability of the reference frequency fr, but in the present invention, the oscillation frequency f2 of the second local oscillator 2 during reception is divided by the frequency divider 15 and used.
This f2 has sufficient functionality for transmitting and receiving SSB waves, which require much more severe frequency stability than FM waves, so there is no problem with the stability of the reference frequency and fr. However, in order to obtain the desired frequency F1' with the VCO 11, it is necessary to set the division ratios of the frequency dividers 12 and 15 so that F1' and fr have an integer relationship, but the details will be explained later. This will be described in the Examples section.

Frequency modulation of the oscillation frequency F1' is carried out by superimposing the audio signal from the microphone amplifier on the control voltage Vc, but this method is relatively easy to obtain an FM wave with good frequency stability, so it has recently been used. Used a lot.

The FM signal of frequency F1' created in this way is added to the intermediate frequency side of mixer M1, mixed with the oscillation frequency f1 of local oscillator 3, and outputted as the FM signal of the operating frequency to the high frequency side of mixer M1. and power amplifier P
It is transmitted from the antenna through A.

[0019]

[Operation] In Figure 1, if the operating frequency is F0, then
The frequency relationship in the receiving state of a frequency conversion type radio transmitter/receiver is F1 = F0 ±f1, and when transmitting, the above equation is modified to

From [Equation 1], it can be seen that the operating frequency is exactly the same for both transmission and reception, but in the FM modulation circuit of the present invention, the operating frequency can also be obtained by adding the FM signal of frequency F1 from the intermediate frequency side of mixer M1. The FM transmission signal of F0 is amplified by the high frequency power amplifier PA and sent out from the antenna, allowing transmission and reception at the same operating frequency.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an example of the circuit configuration of a radio transmitter/receiver to which the present invention is applied, mainly showing the circuit configuration in an FM transmission state.

[0021] Regarding the frequency relationship of each stage, first, the operating frequency F0 can be continuously used in the range of 0 to 30 MHz.

The first intermediate frequency is very high at 70.455 MHz, but this is because it is effective in removing image interference and reducing spurious.
It also has the advantage of being able to extend up to MHz. The first local oscillation frequency f1 is f1 = F0 + F1 = (0 to 30) + 7
0.455=70.455 to 100.455 MHz, which is also very high, but a stable and precise oscillation frequency is obtained by the PLL controlled oscillator 3 and the electronic tuning means 4 that sets its oscillation frequency.

During reception, the first intermediate frequency F1 is converted to a second intermediate frequency F2 of 455 kHz by the second mixer M2.
In the FM reception mode, the signal is demodulated by a discriminator via a limiter amplifier and output as an audio signal AF. The second local oscillation frequency for the second mixer M2 is F1 - F2 = 70.455 - 0.455 = 70MH
z, which is 100Hz required for SSB communication.
The following frequency fluctuation is about 1.4 x 10-6 or less, which is not an easy value even for a crystal oscillator. Therefore, in the circuit of this embodiment, by incorporating the second local oscillation frequency f2 into the PLL circuit of the first local oscillator 3, when f1 fluctuates by ±Δf, f2 also changes by ±Δf. , the first intermediate frequency is F
1 ±Δf, and the second intermediate frequency F2 is F2 = (F1 ±Δf) - (f2 ±Δf) = F1
= f2, this is based on the principle that the second intermediate frequency F2 is not influenced by Δf. Since this method is known as a frequency drift cancellation method among those skilled in the art, detailed explanation will be omitted.

In the frequency modulation circuit of this subject, the oscillation frequency of 70 MHz of the second local oscillator 2 is divided into 1 by the frequency divider 15.
5kHz obtained by dividing the frequency by 4,000 is the reference frequency fr
This is a PLL controlled oscillation frequency modulation circuit 1.

This PLL circuit 1 includes a VCO 11, a frequency divider 12 that divides its oscillation frequency F1' by 14,091, a phase detector 13 that compares the phase of the divided frequency with a reference frequency fr, and The configuration is such that the oscillation frequency is controlled by adding the control DC voltage Vc obtained from the phase difference output through the LPF 14 to the VCO, and the microphone output is connected to the amplifier MA.
By superimposing and adding the amplified audio signal to the control voltage Vc, the VCO oscillation frequency F1' is frequency modulated.

Since the oscillation frequency F1' is determined by the reference frequency fr and the division ratio of the frequency divider 12, F1'=fr×14,091=5×14,09
1=70.455MHz, and the first intermediate frequency F1
, the first mixer M1 mixes it with the first local oscillation frequency f1 to obtain the same operating frequency F0 as at the time of reception.
FM signal waves are supplied to the antenna through the power amplifier PA.

The PLL controlled oscillation frequency modulation circuit 1 used here has better frequency stability and modulation distortion than the VCXO type, but for this purpose a sufficiently stable reference frequency fr is required.
In the present invention, the reference frequency fr
Since the second local oscillator is used as the second local oscillator, the relationship will be discussed below.

[0028] Since the frequency stability of a multi-mode wireless transmitter/receiver like this embodiment is originally designed to suit the SSB wave, which has the most severe conditions, the frequency stability of each oscillator is F.
Although there is sufficient margin for M waves, the influence of the frequency drift canceling operation used in this example circuit will be investigated. In the PLL oscillator 1, when f2 changes by Δf, f1' in this case becomes f1'=f1 ±Δf due to the above-mentioned drift canceling operation. The output frequency F0' of mixer M1 is

[Equation 2] Therefore, when the second local oscillation frequency fluctuates by Δf, the operating frequency F0' is the normal operating frequency F
-0.0065Δf for 0, and the frequency fluctuation is Δ
It has been reduced to less than 1/100 of f, and although it is not a complete drift cancellation, it can be seen that the drift is sufficiently suppressed.

The only condition for implementing the present invention is that the reference frequency of the PLL oscillation modulator 1 is fr and the second local oscillation frequency f
2 and the first intermediate frequency F1 so as to have an integer ratio relationship. In this implementation circuit, f
Although r is set to 5 kHz, in this circuit, the time constant of the LPF 14 is set sufficiently large for modulation purposes, so there is no problem in setting fr low.

[0030]

Effects of the Invention In the FM transmitting circuit of the present invention, the first oscillation frequency modulator produced by a PLL-controlled oscillation frequency modulator whose reference frequency source is the second local oscillator of a multi-mode radio transceiver using a multiplex conversion method.
Since the configuration is such that the FM signal wave at the intermediate frequency is transmitted at the same operating frequency as the first mixer receives it, (1) an FM wave with good frequency stability and little distortion can be obtained. (2) Transmission and reception of the same frequency can be performed automatically. (3) Even in the case of a frequency drift cancellation method in which fluctuations in the second local oscillation frequency are compensated for by the first local oscillation frequency,
Although it is not a complete cancellation, a sufficient drift reduction effect can be obtained. It has the following effects.

[Brief explanation of the drawing]

[Fig. 1] Basic configuration diagram of the FM transmitting circuit of the present invention

[Figure 2] Example diagram of the present invention

[Figure 3] (A) is a block diagram of the receiving state of the multiplex conversion transceiver (B) is a block diagram of the transmitting state

[Explanation of symbols]

1 PLL control oscillation frequency modulation circuit 2 Crystal oscillator 3 PLL oscillator 11 VCO 12, 15 Frequency divider 13 Phase detector 14 LPF M1, M2 Mixer stage F1, F2 Intermediate frequency f1, f2 Local oscillation frequency fr
Reference frequency F0 Operating frequency

Claims (1)

[Claims] 1. At the time of reception, a PLL-controlled variable frequency oscillator is used as the first local oscillator of the first mixer that converts the reception frequency to the first intermediate frequency, and a second mixer that converts the first intermediate frequency to the second intermediate frequency. In a multi-conversion superheterodyne multimode radio transceiver using a fixed frequency oscillator as the second local oscillator of a mixer, in the FM transmission mode, the PLL oscillator is controlled by a reference frequency based on the second local oscillator frequency. A modulation signal is applied to the VCO to generate an FM signal equal to the first intermediate frequency, and this is applied to the first intermediate frequency.
In addition to the intermediate frequency side of the mixer, the F is mixed with the first local oscillation frequency in the first mixer to send out the FM wave of the operating frequency.
M transmission circuit.