Applications of Load-Pull Systems in Transmission Lines
The term load-pull is used to describe the method in which a changing impedance is delivered to a device under test or DUT. The reason this is done is to determine the systems performance and indicate the conditions in which that deliver that particular performance in a network. A load-pull system can be very useful in assessing what a network needs to operate at an efficient rate, also it can indicate that a network is not operating at an efficient rate so the user takes the necessary steps to improve it.
With a transmission line, a user is more likely to use a load-pull to test its efficiency with a transistor to observe its performance. The information obtained by the load pull-would indicate how well the transmission line is operating. With this information the user could improve the transmission line efficiency. There are different types load pull systems, passive load-pull and active load-pull. The difference between the two systems is that the passive load-pull system uses high speed measurements while the active load –pull systems are used in applications that require high reflection coefficient values. Each of these load-pull systems can include a closed loop feature. This closed loop feature allows the system to act as a feedback back network. The main drawback of a closed loop active load-pull system is the risk or oscillations that can happen because of its design as a feedback system. Recent advances in the system incorporated a highly selective filter in the loop to lessen the oscillation problem. This highly selective filter adds complexity to the set up in addition to increased costs. The name of the of the new system design that addresses the oscillation issue in a load-pull system is called envelope load-pull. Another type of load-pull system is called hybrid load-pull. It is a passive impedance tuner and an active load-pull used together to achieve the wanted functionality of the system. The quarter wave transform is used in load-pull systems to fulfill the needs of fundamental load-pull measurements. The Klopfenstein transformer is used to replace the quarter wave transformer because it has bandwidth limitations. The enhanced loop load-pull technique that allows for higher Γ using the pre-matched load-pull system. The two latest developments in load-pull systems are the enhanced load-pull and the envelope load-pull techniques. For more information on load-pull and smith charts I would suggest reading “Lines and Fields in Electric Technology”.
I found this article about applications of load-pull systems in transmission lines very informative. This article was directly related to some of the topic we cover in class. This article did not impact my understanding of the smith chart. To clarify the unknown terms or concepts in this article I researched them online.
Amateur Radio by Prof. Marantz Extra Credit
Last Thursday at the presentation you gave you discussed amateur radio. Before you spoke about amateur radio you explained the difference between professional radio and amateur radio. The difference is obvious though it did not seem that way at first. Professional radio is just that, a profession. People get paid to be on professional radio. It’s a business, companies sponsor with commercials and so on. Amateurs are in charge of amateur radio. Using the word amateur to describe that they are not professional, this means that amateur radio users voluntarily become a user.
What is amateur radio? Amateur radio is using a specified radio frequency range for private use. Private use can be recreational to communicate with other users and also experimentation. Just to see who you can communicate with using amateur radio. The most important use of amateur radio might be emergency communication. When all other communication is down in wake of disaster or tragedy, amateur radio can be used. During 9/11 terrorist attacks the whole city was trying to communicate with their loved ones using land lines and cell phones. But due to traffic and network issues most people received busy signals, if that. But those amateur radio users were able to communicate with others and also provide vital information that peopled needed after the towers went down. As seen in the video you showed during the presentation. Notable amateur radio users for emergency communications are FEMA (Federal Emergency Management) and SATERN (Salvation Army Team Emergency Radio Network).
Methods of communication for amateur radio are AM and FM in analog. For digital, FSK, QPSK and spread spectrum can be used. To obtain an amateur radio license an exam is given. The sky is the limit with using amateur radio. You can meet people around the world and see how far you can communicate. There are also contests that are held to see how many people you can contact over a given amount of time.
I found this presentation very informative and interesting. I was surprised to learn that FEMA and other tragedy management organizations used amateur radio. After you explained that amateur radio is most likely the only way you would be able to communicate during a tragedy, it made perfect sense that such organizations would utilize it.
