![]() Never adjust the trimmer at the port where the load is removed. Then, load 2 is removed and the trimmer at port 5 is adjusted for maximum isolation. First, load 1 is removed, and the trimmer at port 6 is adjusted for maximum isolation (deepest null). ![]() The reverse response or isolation tuning is done using the setup shown in Figure 6. Check the insertion loss at the operating frequency against the manufacturer’s specifications. The forward response of the isolator is very broadband. The peak of the response should be at the operating frequency, and the curve should be symmetrical. The forward response of the isolator is tuned by adjusting the trimmers at ports 1, 2, 3 and 4. The situation gets more interesting when a dual isolator is tuned (Figure 5). The logarithmic display of the spectrum analyzer/tracking generator allows much greater range for tuning the isolator for maximum isolation. Obviously, the wattmeter element would have to be very sensitive in order to get a sufficient reading to properly tune port 3 for the deepest null.Ī better way to tune port 3 for maximum isolation is shown in Figure 4. If the transmitter output power is 100 watts, then the power appearing at port 2 will only be 0.1 watts or 100 milliwatts. Suppose that the isolator has an isolation of 30 decibels. Actually, when using this method, tuning the isolator to the deepest null may be difficult, at best. Also, when using the setup in 3B, it may be necessary to use a low-power element in the wattmeter to tune for minimum power. Using the setup at B, it is important that the transmitter power not exceed the power rating of the dummy load connected to port 3 of the isolator. Using the setup in 3B, the load port (3) is tuned for minimum power on the wattmeter. Using the setup in Figure 3A, the input and output ports (1 and 2) are tuned for maximum power on the wattmeter. A through-line wattmeter is connected between the output port of the isolator and a 50-ohm dummy load. ![]() This ensures that the reflected signal at the reflected port of the RLB is caused predominately by the mismatch at port 1 of the isolator and not by any reflected signal from the output port of the isolator.Ī simple method of tuning a single isolator is shown in Figure 3. It is important to terminate the output of the isolator with a 50-ohm dummy load. The test setup for using this method to tune the input port is shown in Figure 2. One method of tuning the input port is to use a return loss bridge (RLB). There will always be some residual reflected power at the input port, even when the load connected to the output port (port 2) is a perfect 50-ohm load. It is important that the trimmer at the input port (port 1) is tuned for minimum reflected power at port 1 so that the transmitter “sees” very little reflected power. Any reflected power at port 3 will be transferred back to port 1, the input port. Any reverse or reflected power flow will be dumped into the RF dummy load at port 3. The arrow indicates forward flow of RF power. The objective is to tune the isolator so it presents the minimum insertion loss in the forward direction and maximum insertion loss (isolation) in the reverse direction.įigure 1 shows a block diagram of a simple single isolator. Preferably, the isolator should be tuned in its final installed position. Several techniques can be used, depending upon the type of test equipment available. ![]() This article focuses on the proper tuning of the RF isolator. Last month, the operation of RF isolators was discussed in detail. ![]()
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