Cable test is first understanding for any RF Engineer here i write how to test cable integrity and Cable loss and testing of Transmitter in gsm.
Cable Integrity Test
- Cable integrity is checked by measuring VSWR.
- A good known cable is connected from the test transmitter to the wattmeter.
- The cable under test is placed between the wattmeter & 50 Ohms load.
- Forward and reverse power levels are measured and VSWR can be calculated as ,
- Each cable should be checked and any that exhibit greater than 1.2 : 1 VSWR must be replaced.
- Cable integrity check must be performed on all jumpers and antenna feedlines.
- All cables used for testing must be measured and clearly labelled with insertion loss before they are used.
- These are normal wear items and so it is important to replace any cables that become kinked or frayed or that are worn or damaged connectors.
Step 1 Test
- Connected a cable ‘A’ directly to the wattmeter.
- Terminate the other end of the wattmeter with a 50 ohms resistance.
- Insert 1 Watt element in forward position.
- Adjust to full deflection .
- Record reading ‘A’
Step 2 Test
- Connect cable ‘B’ as shown.
- Turn transmitter on.
- Record reading ‘B’.
- Cable Loss for cable B in dB = 10 log10(B/A)
- If the propagation test is being done for model tuning to produce a generic model for macro cells, then a high point in the particular area has to be selected.
- The transmitter and the transmit antenna will be placed at this point (say the roof of the building ).
- The transmit antenna is connected to the transmitter via a RF cable.
- Check to see that the cable is connected properly and tight.
- Loosely connected or faulty cable can increase the VSWR.
- A test frequency has to selected from the frequency band allocated to the operator. Set the transmitter to this test frequency.