Electronika LDMOS UHF SERIES, Руководство пользователя, Страница: 45 / 52

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CALIBRATION PROCEDURE
- Technical characteristics
Power supply voltage 32V (± 2%)
Polarisation current 1.0 cold for each device (2A total), ± 0.1A
Gain for low signal Not less than 13dB in the 470-860MHz band (± 1dB)
Compare to the typical curve eclosed
- Adjustment procedure
Polarisation current calibration 32V stabilised power supply
10A amperometer
Gain curve Network analyser
- Adjustment points description
R7-R8 (Trimmers) Adjust the current absorbed in stand-by (1.0A per device)
- Calibration steps
STEP 1: Close the input and the output of the module by connecting them to a 50
Ω Ω Ω Ω Ω
dummy load and
connect the spectrum analyser through a directive sample, in order to look for self-oscillation of the module,
if any (anyway the module has been designed so that it would not self-oscillate even if totally de-coupled,
without any input or output load).
STEP 2: Check the voltages of the polarisation circuits without assembling the transistors first:
connect the 32V power supply to the proper turret by means of a fastening screw, then give power and check data:
- the stabilised voltage on the zener diodes DZ1 and DZ2 is about 15V compared to the ground;
- the stabilised voltage on the zener diodes DZ3 and DZ4 is about 6.8V compared to the ground;
- the voltage on the pads to which the gates of the LDMOS transistors will be soldered (R23 and R24 resi-
stors side) changes from 0V to a maximum value of about 6V when moving the relevant trimmer (R7-R8).
STEP 3: Check the work of the protections.
- Set both trimmers so that there is a value of about 4.5V on the pads of the gates;
- solder some wire to the pad between the two LEDs, next to the serigraphy of the input hybrid H1;
- in order to check the work of the protections aboard, a power of about 4V has to be supplied to the wire,
for example by touching with it the reophore of C23 or C24 which is not connected to ground; the two red
LEDs will immediately light up and the two RF transistors will be switched off at the same time: the polarisation
current (2A) will decrease to 0 and of course the gain curve displayed by the spectrum analyser will decrease;
- after this it is
important to restore the position of the two trimmers for the minimum voltage! Then
disconnect the 32V power supply.