JPH02102463A - Antenna impedance measuring instrument - Google Patents

Abstract

PURPOSE:To reduce the influence of radio interference and to take an accurate measurement by providing an intermediate frequency narrow band-pass filter, a detector, and a low-frequency band-pass filter. CONSTITUTION:The output signal of la preselector 15 is mixed by a mixer 16 with the local oscillation signal from a local oscillator 12 and converted to an intermediate frequency. This intermediate frequency signal is passed through the intermediate frequency band-pass filter 8 which has a narrow band width of + or - several tens Hz. Then the received signal passed through the filter 8 is amplified by an amplifier 17, detected by the detector 9, and then sent to the low-frequency band-pass filter 10 to extract a modulated wave, which is multiplied by a multiplier 11 up to the audio frequency of human beings. Then necessary signals such as higher harmonic components generated by the multiplication are removed by the band-pass filter 14 and only a modulated wave which is free from radio interference can be heard through a receiver 18. At the same time, the signal is indicated on a meter 23.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an antenna impedance measuring device that measures the impedance of an antenna, particularly an antenna at a medium wave broadcasting station, using a bridge circuit.

(Prior Art) An antenna impedance measuring device using a bridge has been conventionally available. This measuring device connects the measurement terminal of bridge circuit A to antenna B as shown in Figure 2, and listens to the received frequency signal using receiver C, at the point where the sound is the lowest (output signal zero point). The bridge is balanced by finding the following.

With conventional antenna impedance measurement equipment, there is no desired beam when the bridge is balanced.On the other hand, because medium-wave antennas are extremely sensitive and easily interfere with radio waves from other stations, when the bridge is balanced, there is only interference waves. However, there was a problem in that accurate measurement was difficult.

Moreover, unnecessary interference is always heard through the receiver in the ears of the person taking the measurements, so there is also the problem that the person taking the measurements is bothered by the noise.

In order to solve this problem, a narrowband filter E has conventionally been used in the intermediate frequency stage of the receiving section. However, in the past, the modulation frequency oscillated from the modulation oscillation circuit F, which is the signal source of the bridge circuit A, was approximately 8008m.
Adjust the bandwidth of narrowband filter E to match the modulation wave by ±8
008, but since there are many components in the vicinity of 800 H□ in the interference signal coming in from antenna B, even if narrow band filter E is used, not only the modulated wave but also the interference signal will be filtered through filter E. The interference signal removal effect was low.

Therefore, conventionally, a narrowband filter E with a bandwidth of about ±5011□ has been used;
When using this method, it was difficult to synchronize the receiving section, so it was rarely used.

In addition, in a narrowband filter with a bandwidth of about ±50Hz,
Since the sideband of the received signal modulated by the 800Hz modulation signal is cut off, the modulation by the 800Hz modulation signal is actually cut off and the beat oscillator G in the reception section is used to generate the intermediate frequency (455K) 1. ) than 800 H,
A high (or low) signal was oscillated and the difference between the signal and the intermediate frequency was found to obtain a beat signal of 800H.

(Problems to be Solved by the Invention) However, there is a problem in that the beat signal occurs not only as a desired wave but also as an interference signal, making it difficult to distinguish it by ear.

(Objective of the Invention) The purpose of the present invention is to solve various problems of the conventional antenna impedance measuring device, to be able to perform accurate measurements with much less influence of interference than the conventional measuring device, and to make it possible for the measuring person to To provide an antenna impedance measuring device which does not suffer from noise and also solves the problems of the beat method.

(Means for Solving the Problems) In order to achieve the above object, the antenna impedance measuring device of the present invention has the following configuration.

A first aspect of the invention, as shown in FIG. 1, includes a bridge circuit 2 connected to an antenna 1, a signal generating section 3 serving as a signal source of the bridge circuit 2, and a receiving section receiving signals from the bridge circuit 2. In the antenna impedance measuring device equipped with 4, the signal generating section 3 has an R
The receiving section 4 is equipped with at least an RF oscillator 5 that oscillates an F-fold signal and a modulated wave oscillator 6 that generates a modulated signal of several tens of Hz that modulates the RF signal. A frequency converter 7 that converts a signal into an intermediate frequency, an intermediate frequency narrowband filter 8 with a bandwidth of several tens of Hz, a detector 9 that detects the intermediate frequency signal that has passed through the filter 8, and a detector 9 that detects the intermediate frequency signal that has passed through the filter 8. At least a low frequency band filter 10 that passes the modulated wave and a multiplier 11 that multiplies the signal passed through the filter 10 to a human audible frequency are provided, and either the signal generating section 3 or the receiving section 4 includes: A local oscillator 1 comprising an automatic frequency control section 13 in which the oscillation frequency of the local oscillator 12 of the frequency conversion section 7 changes in conjunction with a change in the frequency of the RF oscillator 5.
2. An antenna impedance measuring device characterized by comprising at least the following.

A second aspect of the invention is the antenna impedance measuring device according to the first aspect, wherein the receiving section 4 is provided with a bandpass filter 14 for removing unnecessary signals such as harmonic components generated due to multiplication by the multiplier 11. It is characterized by this.

A third aspect of the present invention is the antenna impedance measuring device according to the first aspect, in which on the output side of the bandpass filter 14,
It is characterized by being provided with a meter 23 that displays the output.

(Function) To measure the impedance of the antenna I shown in FIG. 1 with the antenna impedance measuring device of the present invention, the antenna I Connect the .

In this case, the RF multiplied signal oscillated from the RF oscillator 5 in FIG.
0H,) and is sent to the bridge circuit 2, and from the bridge circuit 2 to the preselector 15, where it is interfered with through the air Ill.
Some of the signals from other stations are removed.

The output signal from the preselector 15 is mixed with the local oscillator signal from the local oscillator 12 in a frequency conversion mixer 16 and frequency-converted to an intermediate frequency. The intermediate frequency signal converted here has a bandwidth of several tens of Hz (for example, ±50
8Z) and a narrow intermediate frequency narrow band filter 8. In this case, since the modulated wave is as low as several tens of H (for example, 401), this modulated wave is not cut off.

The received signal that has passed through the intermediate frequency narrow band filter 8 is sent to the amplifier 1.
After being amplified in step 7 and detected in detector 9, the modulated wave is sent to a low frequency band filter (40H,) 10 to extract the modulated wave, and then multiplied by a multiplier 11 to a human audible frequency. Unnecessary signals such as harmonic components generated due to multiplication are removed by bandpass filter 14, and only modulated waves without interference are heard by receiver 18. At the same time, the signal is also transmitted to the meter 23.

Furthermore, in the present invention, when the frequency of the RF oscillator 5 is changed, the local oscillator signal oscillated from the local oscillator 12 changes in conjunction with the change in frequency. Furthermore, a PLL configured by a tuning mixer 20, a phase comparator 21, and a crystal oscillator 22
(Phase locked loop) always generates a signal with a frequency higher than the measurement frequency by the intermediate frequency (455KH,). Therefore, if the measurement frequency is set with the RF oscillator 5, the receiving section 4 side can automatically be tuned, and no out-of-tuning occurs during use.

(Embodiment) FIG. 1 shows an embodiment of the antenna impedance measuring device of the present invention.

In FIG. 1, 1 is an antenna to be measured at a broadcasting station, and 2 is a bridge circuit. The bridge circuit 2 is the same as that used in conventional antenna impedance measurements.

3 in FIG. 1 is a signal generator, which includes an RF oscillator 5.
and a modulated wave oscillator 6.

The RF oscillator 5 is capable of oscillating up to 500KH to 1650KH. Modulated wave oscillator 6 is 40 Hz
This makes it possible to oscillate low-frequency modulated waves. This 40
Hz is a frequency range in which there are very few audible components of interference waves transmitted through the antenna (most of the audible components are at 100 H! or higher).

4 in FIG. 1 is a receiving section, and a preselector 15 is shown here.
, a frequency conversion mixer 16, an intermediate frequency narrow band filter 8, a detector 9, a low frequency band filter 10, a multiplier 11, a band filter 14, and a tuning mixer 20.
, a phase comparator 21 , a crystal oscillator 22 , and a local oscillator 12 , and the local oscillator 12 and preselector 15 are arranged to operate in conjunction with the RF oscillator 5 of the signal generating section 3 . (Local oscillator 12 and phase-locked loop 13
The preselector 15 is a bandpass filter for removing signals from other stations interfering with each other through the antenna 1 and passing the RF multiplied signal oscillated from the RF oscillator 5. It is.

Reference numeral 7 in FIG. 1 is a frequency conversion section, which converts the received signal received through the preselector 15 into an intermediate frequency, and is composed of a frequency conversion mixer 16 and a local oscillator 12. .

The intermediate frequency narrow band filter 8 has a center frequency of 455KH.
, is a narrowband crystal filter with a bandwidth of ±50Hz.

The amplifier 17 and detector 9 are general-purpose ones.

The low frequency band filter 10 extracts a 40 Hz modulated wave oscillated from the modulated wave oscillator 6, and has a center frequency of 4 oz and a bandwidth of ±2 H in accordance with the modulated wave.
It is set to about z.

The multiplier 11 converts the detected signal into a human audible frequency,
For example, it is possible to multiply up to 960H, (40H, X24).

The bandpass filter 14 removes unnecessary signals such as harmonics generated by multiplication by the multiplier 11, and has a center frequency of 960H and a bandwidth of ±50Hz.

The tuning mixer 20 is a general-purpose one, and the crystal oscillator 2
2 oscillates a reference signal of 455 KH, and the local oscillator 12 oscillates a local oscillator signal with a frequency higher than the frequency of the RF signal oscillated by the RF oscillator 5 by an intermediate frequency (455 Kl(z)). It is.

The phase comparator 21 calculates the difference between the local oscillator signal oscillated from the local oscillator 12 and the RF signal oscillated from the RF oscillator 5.
The reference signal (455KHz) oscillated from the crystal oscillator 22
), the oscillation frequency of the local oscillator 12 is exactly 455 KHz compared to the frequency of the RF oscillator 5 due to P and LL.
The local oscillator 12 automatically adjusts the signal to
(Effects of the Invention) The antenna impedance measuring device of the present invention has the following effects.

(1) The modulation wave frequency is a low frequency of about 40 Hz, which is a frequency range in which the audible component of the interference wave is extremely small, so it is easy to separate it from the interference component, and highly accurate measurement is possible. By the way, with the conventional measurement device, it was difficult to measure even if the interference wave was 10KH away from the measurement wave, but with the measurement device of the present invention, it was confirmed through experiments that it is possible to measure even when both waves overlap. Ta.

(2) Since the modulation frequency is set to a frequency that can pass through the intermediate frequency narrowband filter 8, there is no need to create a beat signal in the receiver as in the conventional case, and all problems when using beats are solved. be done.

(3) Since the local signal oscillated from the local oscillator 12 changes in conjunction with the frequency change of the RF oscillator 5, if the measurement frequency is set with the RF oscillator 5, the receiving section 4fl will automatically be tuned; And no synchronization occurs during use.
This makes it extremely easy to handle.

(4) Since the low frequency band filter 10 through which only the modulated wave passes is provided after the detector 9, most of the interference components are removed.

(5) Since the multiplier 11 is provided, it is possible to listen to modulated waves as low as 40 Hz.

(6) Since the bandpass filter 14 is provided after the multiplier 11, harmonics generated by multiplication and the remaining interference components are removed.

(7) Since a meter is also used to detect the balance of the bridge, the balance point of the bridge can be determined not only by the ear but also by the meter. In this case, if the interference cannot be sufficiently removed,
The meter reading may fluctuate, but in this case, when the needle vibration has stabilized to some extent and is below a certain value, it is possible to measure by taking the midpoint between the two dial positions of the bridge circuit and treating it as the equilibrium point. .

(8) By combining the above measures, even if the measurement frequency is close to an interference wave, the measurement can be performed with almost no interference noise, and the person taking the measurement will not be bothered by the noise.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the antenna impedance measuring device of the present invention, and FIG. 2 is an explanatory diagram of a conventional antenna impedance measuring device. 1 is an antenna 2 is a bridge circuit 3 is a signal generator 4 is a receiver 5 is an RF oscillator 6 is a modulated wave oscillator 7 is a frequency converter 8 is an intermediate frequency narrow band filter 9 is a detector 10 is a low frequency band filter 11 is a multiplier The device 12 is a local oscillator 13, the phase-locked loop 14 is a bandpass filter 23, and a meter

Claims (3)

[Claims] (1) In an antenna impedance measuring device comprising a bridge circuit 2 connected to an antenna 1, a signal generating section 3 serving as a signal source of the bridge circuit 2, and a receiving section 4 receiving a signal from the bridge circuit 2, The signal generating section 3 includes an RF oscillator 5 that oscillates an RF signal to be applied to the bridge circuit 2.
and a modulated wave oscillator 6 that generates a modulation signal of several tens of Hz for modulating the RF signal, and the receiving section 4
includes a frequency converter 7 that converts the modulated wave signal given from the bridge circuit 2 into an intermediate frequency, an intermediate frequency narrowband filter 8 with a bandwidth of several tens of Hz, and a frequency converter 7 that detects the intermediate frequency signal that has passed through the filter 8. a low frequency band filter 10 of several tens of Hz that passes the modulated wave of the detected signal;
At least a multiplier 11 for multiplying the signal passed through the filter 10 to a human audible frequency is provided, and either the signal generating section 3 or the receiving section 4 receives the oscillation frequency of the local oscillator 12 of the frequency converting section 7. An antenna impedance measuring device comprising at least an automatic frequency control section 13 that changes in conjunction with changes in the frequency of the RF oscillator 5. (2) The antenna impedance measuring device according to claim 1, wherein the receiving section 4 is equipped with a bandpass filter 14 for removing unnecessary signals such as harmonic components generated due to multiplication by the multiplier 11. (3) An antenna impedance measuring device according to claim 1, characterized in that a meter 23 for displaying the output is provided on the output side of the bandpass filter 14 of the receiving section 4.