2.4.3. Measurement of the maximum transmitter frequency deviation.
Set the FM modulation to the "broad band" (25 kHz) position using the smart button key on the transmitter/receiver unit. On RST–430: press the F1-button, set the modulation voltage at 0.04 V, press ENTER in order to confirm the set values and display them on the screen. Similarly, press the F2-button and set the frequency of the modulating signal at 3.00 kHz, press "ENTER", then press "ESC" to go to the transmitter parameters measurement menu
Supply the modulating signal to transmitter input. For this purpose connect the MODULATOR INPUT of the cable-adapter and the radio tester output AF OUT
with the cable.
Activate the "transmission
" signal by pressing the PTT
-button of the cable- adapter. Press the F3-button (deviation measurement) to get the reading on the screen of the radio tester. Release the push-to-talk switch
The value of the frequency deviation measured with the radio tester in the "broad band" mode (25 kHz) must not exceed ±4.1 kHz
, and in the "narrow band" mode (12.5 kHz) — not to exceed ±2.1 kHz accordingly
. In case of exceeding of the specified values, carry out a correction of the transmitter. Set such value of the transmitter modulation voltage, at which the transmitter frequency deviation will be equal to 3 kHz
(in the "narrow band" mode — 1.5 kHz
Increase the modulation voltage, at which the transmitter frequency deviation is equal to 3 kHz (in the "narrow band" mode — 1.5 kHz
), by 10 dB
(by 3 times
) and measure the deviation by subsequently setting a number of modulation frequency values from 300 Hz to 3,000 Hz. The maximum measured value of the transmitter frequency deviation in this range of audio frequencies must not exceed 5.0 kHz
in the "broad band" mode and 3.3 kHz
— in the "narrow band" mode.2.5. Measurement of receiver parameters.
The equipment stays connected as specified in Pic. 2. Set the handle of the RRG volume control to the middle position.2.5.1 Measurement of receiver sensitivity.
Switch-off the noise suppressor (enable the the SQL
mode of the display of the transmitter/receiver unit using the smart button. Use the ▲, ▼ -buttons to reduce SQL to the values within 15–20 units). By pressing the ESC
button on the RST-430 keyboard, go to the settings menu
of the HF generator signal parameters.
Pressing the keyboard buttons (F1, F2, F3, F4), set the values of the output signal parameters of the HF generator. Confirm each value setting by pressing the ENTER
- F1 (frequency): set the value of the frequency of the selected radio station channel;
- F2 (output): set the level value of the output signal of 110 dBm (approx. 0.5 µV);
- F3 (deviation): set the frequency deviation value of the output signal of 3.00 kHz;
- F4 (LF frequency): set the value of the output signal modulation frequency of 1,000 kHz;
Activate the mode of measurements of the receiver parameters by pressing the ESC
button. After the menu of the receiver parameters measurements
has appeared on the screen, press the F1 button on the keyboard (SINAD) and measure the signal/noise ratio (in %
), the readings will be available in the lower line of the screen.
Achieve the signal/noise ratio of 25% by changing the of level of the HF generator output signal
The receiver sensitivity is defined as a signal level, at which the signal/noise ratio is equal to 12 dB, or 25%.
If the attenuation of the signal from the HF-generator (120 dB) is not sufficient, attach an attenuator with the fixed attenuation value (for example, D2-32, 20 dB) to the HF-generator output and then connect to it the cable from the antenna output of the radio station. Then, when processing the measurements result, the attenuation value, which is read from the tester screen, is added to the attenuation of the attenuator (for example: 106 dB + 20 dB =126 dB).
Convert the value of the signal level from dBm to µV using the enclosed table. The measured value of the receiver sensitivity must not exceed 0.25 µV