If you have some kind of VNA you have to be sure your measurements are correct. And this is true: the non-calibrated tool always returns incorrect data regardless of how nice and correctly do they look. To avoid such an inaccuracy of measurements you have to calibrate your device first. There is a well-known procedure named OSL calibration. The OSL calibration is being made against the cable used to measure some device. This is required to subtract the cable from the results of measurements. This is why you have to store results of calibration to separate files (if your device allows you to do this) and then use the corresponding file accordingly.
OSL stands for "Open-Short-Load". These words describe three types of measurement standards, allowing you to ensure you have got nothing, but the true measurements. Technically these standards are the same inside but different in the type of connector.
The Open standard is just a connector with no added value to it. Technically you may not have the Open load in your collection if your activity is dedicated to the HF only. In this case, you can use nothing when doing the Open calibration. This kind of the Load affects your calibration only if the length added by the Open load to the calibrated cable is so significant so it brings too big error in further measurements you make after this calibration. But again, on HF the effect is insignificant.
The Short standard is a connector having the central wire and the braid soldered together.
The Load standard is a connector having 50 Ohms resistor soldered between the central wire and the braid.
Below is the picture of the Open, Short and Load standards I have made some time ago. They still have no electromagnetic shields around the pins, but this is a quickly made loads I have done to see what the OSL calibration is.
For the Load standard, I used two 100 Ohms SMD resistors of type 0805 soldered in parallel. This gave me exactly 50 Ohms of resistance. The 0.3 Ohms is the resistance of the multimeter wires.
Why two? From the one side, there is no 50 Ohms resistor in the standard set of 5% resistors you can buy everywhere. From the other side, two resistors can handle more power than the single one. In my case, two SMD resistors can handle 2x0.125 = 0.25W or +24 dBm.
Why SMD? Using this type of resistors allowed me to have the load as small as possible. Also, in the case of planar resistors, you have to bend their pins and make them curly so that the overall construction will have some added capacitance. Sure, for the HF measurements this capacitance has almost no effect, but VHF and, moreover, UHF the effect can be dramatically unexpected. So if you plan to do such a kind of loads do not hesitate to do them properly in each case, even if you don't expect any unexpected things like the reactive resistance inside of your products.
Below is a couple of pictures of loads I grabbed out of the page of the blog by AE1S. Very professional work! By the way, looking at these loads I started thinking of reasons I have followed when choosing SMA as a type of connectors for my own projects.
OSL stands for "Open-Short-Load". These words describe three types of measurement standards, allowing you to ensure you have got nothing, but the true measurements. Technically these standards are the same inside but different in the type of connector.
The Open standard is just a connector with no added value to it. Technically you may not have the Open load in your collection if your activity is dedicated to the HF only. In this case, you can use nothing when doing the Open calibration. This kind of the Load affects your calibration only if the length added by the Open load to the calibrated cable is so significant so it brings too big error in further measurements you make after this calibration. But again, on HF the effect is insignificant.
The Short standard is a connector having the central wire and the braid soldered together.
The Load standard is a connector having 50 Ohms resistor soldered between the central wire and the braid.
Below is the picture of the Open, Short and Load standards I have made some time ago. They still have no electromagnetic shields around the pins, but this is a quickly made loads I have done to see what the OSL calibration is.
Why two? From the one side, there is no 50 Ohms resistor in the standard set of 5% resistors you can buy everywhere. From the other side, two resistors can handle more power than the single one. In my case, two SMD resistors can handle 2x0.125 = 0.25W or +24 dBm.
Why SMD? Using this type of resistors allowed me to have the load as small as possible. Also, in the case of planar resistors, you have to bend their pins and make them curly so that the overall construction will have some added capacitance. Sure, for the HF measurements this capacitance has almost no effect, but VHF and, moreover, UHF the effect can be dramatically unexpected. So if you plan to do such a kind of loads do not hesitate to do them properly in each case, even if you don't expect any unexpected things like the reactive resistance inside of your products.
Below is a couple of pictures of loads I grabbed out of the page of the blog by AE1S. Very professional work! By the way, looking at these loads I started thinking of reasons I have followed when choosing SMA as a type of connectors for my own projects.
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