In order to statisfy the applications flexibly, Jingxin develops the tunable filters for the client to debug by themselves, and offers the guideline to rightly tune it as the following example of VHF filter.
1. Re-tuning procedure for tunable filter JX-SF1-152174-215N
The filters are designed to tune over a 15 MHz range and have a typical passband bandwidth of 8 MHz.
2. Equipment required
A network analyzer that can display insertion loss and return loss.
Within the passband, the insertion loss should be ≤ 1.7dB; return loss should be ≥20dB
Hand Tools：6mm open-end spanner; Straight screwdriver
3. Re-Tuning Method
This procedure will describe the process used for a unit previously tuned to a center frequency of 160.3MHz, and a bandwidth 8 MHz range.
As shown in Figure 1, the resonator tuning screws are designated as F1, F2, F3, F4, and F5. These tuning screws determine the center frequency of each pole, as the tuning screws move inward, the frequency will tend to be lower, while the tuning screws move outward, and the frequency will be higher.
F12, F23, F34, F45 are coupling screws, these screws determine the bandwidth of the passband, screws move inward, and can widen the right side of the passband,screws move outward can narrow the right side of the passband.
Figure 1
Step 1: Connect the filter JX-SF1-152174-215N to the configured network analyzer, as shown in figure 2
Figure 2
Step 2：Set a required central frequency of 160.3MHz and bandwidth of 8MHz
Step3:The initial frequency of 160.3MHz±4MHz,Out-of-band rejection frequency 160.3±9MHz and 160.3±14MHz can be seen in the frequency band range, as shown in figure 3
Figure 3
♦ The following steps are the debugging process of central frequency from 160.3MHz to 152 MHz
1) The frequency goes from high to low, in sequence rotate clockwise screws F1、F2、F3、F4、F5 to 152MHz±4MHz,all the tuning screws move inwards ,the frequency of cavity will shift overall from high to low,the passband moves to the left.
Figure 4 shows the change of each tuning screw at a frequency of 152MHz±4MHz.
Figure 4
1) After rotating to tuning screw F5,continue using 6mm spanner slightly loosen the nut;screwdriver rotates the tuning screws, adjust the return loss to specified value,If the insertion loss and return loss on the left can not reach the specified value, the insertion loss and return loss can be reduced by rotating clockwise or counterclockwise the coupling screws F12, F23, F34 and F45 ,as shown in figure 5.
Figure 5
Figure 6 is a complete graph of the center frequency at 152MHz; bandwidth at 8MHz
Figure 6
♦ The following steps are the debugging process of central frequency from 160.3MHz to 174MHz
1）The frequency goes from low to high, in sequence rotate clockwise screws F1、F2、F3、F4、F5 to174MHz±4MHz,all the tuning screws move outwards ,the frequency of cavity will shift overall from low to high,the passband moves to the right.
Figure 7 shows the change of each tuning screw at a frequency of 174MHz±4MHz
Figure 7
2）After rotating to tuning screw F5,continue using 6mm spanner slightly loosen the nut;screwdriver rotates the tuning screws, adjust the return loss to specified value,If the insertion loss and return loss can not reach the specified value, the insertion loss and return loss can be reduced by rotating clockwise or counterclockwise the coupling screws F12, F23, F34 and F45 ,as shown in figure 8
Figure 8
Figure 9 is a complete graph of the center frequency at 166.7MHz; bandwidth at 8MHz
Figure 9
Post time: Sep-30-2021
