Checking The Gain And Frequency Response Of The Filter; 4.1 Steps To Check The Gain Setting - ABB ETL600 Instruction Manual

Revision:
A
11. Using a plastic screwdriver, slowly turn the adjuster screw of coil L1, until the voltage at the level
meter is minimized.
The coil L1 is tuned now.
12. Select coil L2 by setting jumper S3 on P4LM to position L3(!) and repeat the procedure by clicking
Activate f2 to tune coil L2 of P4RX. Note that jumper position L2 of S3 is not used for P4RX.
13. Click Deactivate frequency.
14. Click Cancel.
The filter is tuned now.
4

Checking the gain and frequency response of the filter

The ripple of the pass band and the selectivity of the filter are determined when checking the frequency
response.
The P4RX board may be checked when plugged in the rack, e.g. without the Rx tuning adapter P4LM. This
way the influence of the tuning adapter on the filter is eliminated. Only the Tx tuning adapter P3LL is
required to deliver the required test signals. The RF hybrid must not be plugged onto the Tx tuning
adapter, so that the input of P4RX is disconnected from the system.
For these tests the mini coax (SSMB) connectors on the P4RX front panel are used. The upper connector,
labelled "RX RF-IN" is now used as a test input. The lower one, labelled "RX RF-OUT" is connected to the
level meter (50 Ohm input). Refer to chapter 5 "Test circuits", Figure 2.
For these tests the level meter should preferably have an input impedance of 50 Ohm, but a 75 Ohm type
may also be used. Correction factors for this case are given below. As the test signal from P3LL is now
terminated with 50 Ohm, its level is quite low. In case a wide band level meter is not sensitive enough, use
a more sensitive selective level, but in general a wide band level meter will be adequate.
A level meter like the SPM-33 can also be set to "high impedance" input (e.g. approx. 6 kOhm). Now a
50 Ohm BNC "feed-through" termination directly on the level meter input converts it into a 50 Ohm
instrument. Set scale units to dB.

4.1 Steps to check the gain setting

Refer also to chapter 5 "Test circuits", Figure 2.
1. Plug P4RX directly into the rack.
2. The Tx tuning adapter P3LL is inserted in place of the RF hybrid (P3LE).
3. The P3LL tuning adapter is set as follows during the entire process:
• FUNCTION
• Position of S1
• Position of S2
• Position of S3
• Position of LOAD
4. Connect the BNC connector OUT of P3LL to the 50 Ohm (or 75 Ohm) input of the level meter.
Because the P3LL output is a high impedance source, the signal level at 50 Ohm will be quite small.
But mostly a wide band level meter still will be sensitive enough. If not, use a more sensitive selective
level meter to get reliable
5. In the Tuning Rx RF filter dialog box, click Check Rx RF filter to get the dialog box Check filter.
Click Activate f0. Read the level in dB.
• If a 50 Ohm instrument is used, designate this measured level as A.
• If a 75 Ohm instrument is used, subtract 2.61 dB from the measured level (the P3LL output is a
high impedance source). Designate this result as A.
Note:
The RF hybrid must not be plugged on top of P3LL.
A
L2
FILTER
Don't care
Don't care
measurements.
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