Equipments - Measuring receivers

The measuring receivers used in transmission technique are measuring equipments with technical parameters and services, which allow the measurement of level of the examined signal on a telecommunication equipment. A block diagram of a measuring receiver is shown on the following figure:

Services of the measuring receivers can be summarized in the following points:

Operation modes:

Frequency range: Frequency range of measuring receivers, which is usually broad (0...10,20,100 MHz) is divided into more narrower frequency ranges (these are the so called operational ranges), by circuit reasons. The usual ranges are the following:

Input impedance:

Input impedances have the usual value /75, 150, 600 ohms /. Besides it, the measuring receiver can be used as a voltage measuring equipment with high input impedance. The "high" input impedance is higher compared to the standard impedance values, actually 5-10 kohms.

Input connector:

Sensitivity:

Level range (-120 ... +20 dB)
Sensitivity of measuring receivers can be set with resolution of 1 dB. There are two kind of sensitivities of the measuring receiver in a selective mode:

Selective system:

Selective system works on the principle of the super heterodyne radio. Filter (4) on the input of the selective system provides the filtering out of signals outside the operational frequency range. Mix the selected spectral component with the modulator (6) in the pass band of the filter (7). Pass band of the I. KF (middle frequency) filter is above the operational frequency band, providing the masking of the mirror frequency signals. Filters realizing the selectivity (10,11) are in the frequency band of 100 kHz, because filters can be realized easily in this frequency band. Transposing between the first and second KF is executed by the (9) modulator.

Setting of frequency:

Frequency setting possibility with resolution of 1 Hz - without changing band in the whole operation frequency range - is a basic requirement.

Synchronous tuneability:

When you measure a frequency response, it is practical to measure selectively, because with the help of a selective receiver you can filter the perturbing signals. Synchronous tuning can make the measurement comfortable: tuning signal of the measuring transmitter can be lead to the measuring receiver, and then you can tune both of the equipments with only one operation lever.

It is easy to understand, that the criterium of the synchronous tuning is . Frequency of the fix oscillator of measuring transmitter must be equal with the first middle frequency of the measuring receiver.

Bandwidth:

Band pass filter set of the measuring receiver is suitable for measurement of spectrum and noise. Bandwidths used for a spectrum analysis: 20...100 Hz. Bandwidths used for noise measurement:

Level measurement

Resolution of level measurement is minimum 0.1 dB /0.01 dB is desirable/. There is a digital level measure in most of the measuring receivers. Scale :

Display of the size (level) of the examined signal is in relative units (decibels).
Relative values (levels) are the same as the values written in connection with the measuring transmitter.

Level calibration:

Level calibration is made to the authenticated level source in the measuring receiver.

Measuring field:

We can make impedance, reflexion and symmetry measurements with