JPS6017988Y2 - Television AM sideband observation adapter - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an adapter for observing the AM sideband of a television.

Measuring the sideband strength characteristics of a television video transmitter is
In television transmission technology, it is important and fundamental in relation to frequency characteristics, lower sideband strength characteristics, etc.

However, conventional measurement techniques have shown various unsatisfactory points.

For example, measurements using an N-sideband analyzer involve uncertainties in the amplitude deviation and the frequency of the measurement point, while plotting using a field strength meter improves measurement accuracy but requires a lot of time for measurement and has the disadvantage that it cannot be viewed directly. Therefore, it was common to use both measurement methods together.

Recently, in order to solve the above-mentioned drawbacks, measurements using spectrum analyzers have become popular, and high-precision measurements have become possible. It was necessary to observe at a sufficiently slow sweep speed and use an afterglow display.

The present invention improves the above drawbacks and uses a spectrum analyzer, tracking oscillator, and frequency counter.
The present invention aims to provide a sideband analyzer adapter that has a simple configuration, is inexpensive, and enables highly accurate measurements.

Conventionally, this type of adapter has an output that sweeps near zero frequency, and is frequency offset by mixing the first local oscillation frequency of the spectrum analyzer and the local oscillation frequency inside the adapter.

That is, the tracking oscillator output and the adapter's local oscillator output oscillating at the measurement frequency are mixed and frequency converted to obtain a sweep signal in the video frequency band.

In this method, since the local oscillator of the adapter and the carrier frequency of the transmitter under test are unrelated, there is a frequency error during frequency conversion, and further fine adjustment due to frequency fluctuations is required.

Furthermore, the configuration is complicated and expensive. The present invention relates to an adapter that improves these drawbacks.

Figure 1 shows the adapter of the present invention.
is a video transmitter, the output side of the transmitter is connected to the antenna 2, the input side is connected to the TV test signal generator 3, the input side of the TV test signal generator is connected to the adapter 4, The input side of the adapter is connected to a tracking oscillator 5, the input side of the tracking oscillator 5 is connected to a spectrum analyzer and frequency counter 6, and the device is connected to a small antenna 7.

However, within the video transmitter 1 is a main oscillator M.

In the low power stage modulation method, the frequency is in the W band, and video is modulated in this stage.

Furthermore, the video transmitter 1 includes a local oscillator.

It is for converting the video-modulated IF band frequency to a predetermined television channel frequency (any of the 1st to 62nd channels).

The relationship is TV channel carrier frequency = main oscillator frequency + local oscillator frequency.

Tracking oscillator 5 is spectrum analyzer 6
a, a synchronous oscillator is constructed, and the frequency counter 6b measures the frequency received by the spectrum analyzer 6a during the marker pulse period.

Inside the adapter 4 is the main oscillator M inside the video transmitter 1 described above.

an amplifier 4a that amplifies the signal from the source, and a local oscillator.

An amplifier 4b that amplifies the signal of the error, and peripheral amplifiers 4a, 4
A mixer 4c that obtains a signal with a frequency that is the sum of the frequencies of the signals of b.
A mixer 4d for frequency conversion that mixes the signal from the tracking oscillator 5 and the signal from the mixer 4C to obtain a sweep signal in the video frequency band, and an amplifier 4e for amplifying the output from the mixer 4d. It is equipped with

Since the sweep frequency of the tracking oscillator is synchronized with the reception frequency of the spectrum analyzer, the sweep frequency of the tracking oscillator is converted to a video frequency by the frequency converter 4d, and added to the external input terminal of the TV test signal generator 3. Obtain a composite signal of the video sweep signal.

Next, an explanation will be given using TV channel 4 as an example.

In the fourth channel, the carrier frequency of the video transmitter 1 under test is 171.25 MHz, so when the tracking oscillator 5 oscillates at 171.25 MHz, the frequency of the video signal only needs to be OHz, so the frequency converter 4d The oscillation frequency of the local oscillator added to the oscillation frequency may be the carrier frequency of the video transmitter 1 to be measured, that is, 171.25 MHz.

The relationship between these frequencies is shown in FIG.

In FIG. 2, the horizontal axis represents frequency, where A represents the spectrum of the tracking oscillator and B represents the spectrum after frequency conversion.

FIG. 3 shows typical sideband characteristics.

The above explanation explains the sideband strength characteristics using the fourth channel's fixed wavenumber band as an example, but if you want to observe the lower sideband strength, you can simply widen the reception band of the spectrum analyzer. Furthermore, if the crystal oscillator of the video transmitter under test is used, there is no need to provide a separate local oscillator.

In FIG. 1, a switch S1 is provided between the mixer 4d and the amplifier 4a, and a switch S2 is provided between the mixer 4c.
, the amplifier 4d, and closes only the switch S□, and closes the switch S2 . If S3 is opened, the main oscillator M as an input of the mixer 4d.

Since the oscillation output is given, the sideband characteristics up to the intermediate frequency amplification stage can be observed.

Also, only switch S3 is closed, and switch S1. When S2 is opened, if the signal is taken out from terminal J, it becomes an IF band sweep signal, so the frequency characteristics from the W stage to the RF stage can be observed, so the tracking oscillator can be used even if the input and output frequencies are different. can.

As mentioned above, the output of the mixer that obtains a signal with a frequency that is the sum of the frequencies of the main oscillator and local oscillator of the video transmitter under test and the signal from the tracking oscillator are frequency-converted, and the frequency-converted signal is (b) Since the local oscillator of the transmitter under test is used as the local oscillator of the adapter, there is no need to provide a special local oscillator. It is economical and simplifies measurement.

(b) Since the frequencies of the video transmitter and spectrum analyzer can be synchronized, measurements are simplified, and since frequency errors do not occur during frequency conversion, measurements can be made accurately and there is no need for fine adjustments.

(c) Since the frequency error during frequency conversion is canceled out, there is no need to provide a special marker generator, and the spectrum
It is sufficient to display the frequency at the marker pulse position of the analyzer on a counter, allowing accurate measurement and eliminating the need for fine adjustments due to frequency floating.

It has the following effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the adapter of the present invention, FIG. 2 is a frequency spectrum thereof, and FIG. 3 is a typical sideband characteristic diagram. 1...Video transmitter, 2...Antenna,
3...TV test signal generator, 4...
・Adapter, 4a, 4bt 4e...Amplifier, 4c, 4d...Mixer, 5...Tracking oscillator, 6a...Spectrum analyzer, 6b... ...Frequency counter, 7...
...Medium and small antenna, Mo... Main oscillator, L
. ...Local oscillator, S□, S2. S3...
・Switch, j...terminal.

Claims (2)

[Scope of utility model registration request] (1) Amplifiers 4a and 4b that amplify at least the signals from the main oscillator and local oscillator of the video transmitter, respectively;
A mixer 4C obtains a signal with a frequency that is the sum of the frequencies of the signals of both amplifiers 4a and 4b, and the output of the mixer and the signal from the tracking oscillator 5 are mixed to obtain a sweep signal in the video frequency band. An adapter for observing an AM sideband of a television, which is equipped with a mixer 4b for conversion. (2) Switches S1 . S2゜S
3. The television circumferential sideband observation adapter according to claim 1 of the utility model registration claim.