Humber College Institute of Technology and Advanced LearningRF TECHNOLOGY

Coaxial Cable 2ByAndres Mavare

Professor Carl Hassanali

April 2015ABSTRACT

This report will entails the measurement of the velocity factor and calculation of dielectric coefficient in different types of coaxial cables using return loss and insertion loss methods on a network analyzer due to every type of coaxial cable has its own characteristics that differentiate one from another and suggest which one can be used for certain type of application or even in which frequency must be used.

TABLE OF CONTENTS

ABSTRACT iLIST OF FIGURES AND TABLES. 3LIST OF SYMBOLS. 3ACKNOWLEDGEMENTS... 4INTRODUCTION.. 5EXPERIMENTAL DETAILS....... 7RESULTS AND DISCUSSION.. 10CONCLUSION. 14REFERENCES. 15

LIST OF FIGURES AND TABLES

FIGURE 1 Cellular Base Station Components................................... 5FIGURE 2 Transmitter Section Measurement... 7FIGURE 3 Receiver Section Measurement 8FIGURE 4 Isolation Measurement... 9FIGURE 5 Response Curve for Insertion Loss and Return Loss Transmitter Section10FIGURE 6 Response Curve for Insertion Loss and Return Loss Receiver Section11FIGURE 7 Response Curve for Isolation12

TABLE 1 Transmitter Section Results10TABLE 2 Receiver Section Results11TABLE 3 Isolation Results12

LIST OF SYMBOLS dBm ------ Decibels Power Unit MHz ------ Mega Hertz. Frequency Unit.

ACKNOWLEDGEMENTS

The author would like to acknowledge Humber Institute of Technology for providing a great technological infrastructure that allows students to perform projects in the laboratories with adequate equipment that makes a good hands on learning experience. Moreover a thank you to Professor Carl Hassanali who puts great effort on bringing new knowledge to his students and marking the importance of understand how experiments made in the laboratory are related with field work in the telecommunication area.

INTRODUCTIONCoaxial Cable is one of the most popular means of electromagnetic propagation if a round cross-section of the cable is taken it would be found a single center solid wire symmetrically surrounded by a braided or foil conductor. Between the center wire and foil is an insulating dielectric. Data is transmitted through the center wire, while the outer braided layer serves as a line to ground. Both of these conductors are parallel and share the same axis. This is why the wire is called coaxial! This dielectric has a large effect on the fundamental characteristics of the cable. There are several types of coaxial cables that are used for different applications and their properties differentiate one from another for this report is important to focus on two characteristic on specific, the velocity factor and the dielectric coefficient.The coax cable velocity Factor is the speed an electromagnetic wave travels along a coax cable relative to the speed in a vacuum. The speed at which a signal travels within a coax cable is not the same as an electromagnetic wave travelling in free space instead it is affected by the dielectric that is used within the coax cable, and this has the effect of slowing the signal down.There is another concept important to determinate velocity factor using the length of the coax cable and it is the electrical length; one important factor of a coax cable in some applications is the wavelength of the signals travelling in it. In the same way that the wavelength of a signal is the speed of light divided by the frequency for free space, the same is also true in any other medium. As the speed of the wave has been reduced, so too is the wavelength reduced by the same factor. Moreover there is a characteristic very important for any coax cable the dielectric coefficient that is a number relating the ability of a material to carry alternating current to itself. If resonant lengths of RF coax cable are to be used, then it is necessary to know the velocity factor of the coax cable. It is often possible to determine this to a sufficient degree of accuracy from a knowledge of the dielectric material.

EXPERIMENTAL DETAILSBasically these experiment entails measuring return loss, Insertion Loss and the Isolation between the ports of a cellular duplexer. It is well known that a duplexer is a three port device which one of the port is the Tx combiner the second port is the Rx Multicoupler and the third port is a common antenna for TX and Rx. The objective of the following experiments is to determinate the values of the band pass filter that divide the transmission frequency and the receiver frequency. Furthermore the idea is to analyze if there is an interference between the Tx combiner and the Rx Multicoupler frequencies measuring the Isolation level between them. For these experiment were used a Network Analyzer, a Cellular Duplexer (Cellwave #3404007), coaxial cables and RF adapters. The study of the duplexer was divided in three experiments shown below.1. Transmitter Band Pass Section Measurement

Fig. 2 Transmitter Section Measurement.Procedure Set measure parameter to S11 for Return Loss and S21 to measure Insertion Loss. Calibrate network analyzer for 0Db losses from the coaxial cable. Set up the frequency range from 810 MHz to 910 MHz Connect the equipment as in Fig. 2 in order to measure the transmitter band pass section of the duplexer. Using a marker find two frequencies where power measure for insertion loss is -3Db. With another marker find two frequencies where power measure for return loss is -14Db.2. Receiver Band Pass Section Measurement.

Fig. 3 Receiver Section MeasurementProcedure Set measure parameter to S11 for Return Loss and S21 to measure Insertion Loss. Calibrate network analyzer for 0Db losses from the coaxial cable. Set up the frequency range from 810 MHz to 910 MHz Connect the equipment as in Fig. 3 in order to measure the receiver band pass section of the duplexer. Using a marker find two frequencies where power measure for insertion loss is -3Db. With another marker find two frequencies where power measure for return loss is -14Db.3. Isolation Measurement

Fig. 4 Isolation MeasurementProcedure Set measure parameter to S21 to measure Insertion Loss. Calibrate network analyzer for 0Db losses from the coaxial cable. Connect the equipment as in Fig. 4 in order to measure the isolation between transmitter and receiver frequencies. Measure the worst case isolation. This is measuring isolation at the highest frequency of the low pass section and the lowest frequency of the high pass section.

RESULTS AND DISCUSSIONS

After the experiments the results were tabulated in the following tables bellow. Results are divided for each set up of the Duplexer, the transmitter section, the receiver section and the isolation measurement.

Transmitter Section High Band Pass Filter.Insertion LossReturn Loss

Low Freq. (-3dB)867.3 MHzLow Freq. (-14dB)869.1 MHz

High Freq. (-3dB)903 MHzHigh Freq.(-14dB)900.9 MHz

BandwidthBandwidth

35 MHz31.7 MHz

Table 1. Transmitter Section Results

Fig.5 Response Curve for Insertion Loss and Return Loss Transmitter Section

Receiver Section Low Band Pass Filter.Insertion LossReturn Loss

Low Freq. (-3dB)819.3 MHzLow Freq. (-14dB)821.7 MHz

High Freq. (-3dB)854.73 MHzHigh Freq.(-14dB)852.6 MHz

BandwidthBandwidth

35.4 MHz31 MHz

Table 2. Receiver Section Results

Fig. 6 Curve Response for Insertion Loss and Return Loss Receiver Section.

Isolation MeasurementLow FrequencyHigh Frequency

854.7 MHz867.7 MHz

IsolationIsolation

-52dB-53dB

Table 3. Isolation Results

Fig.7 Curve Response for Isolation between Transmitter and Receiver.ObservationsNow that it is well known that a duplexer allows a radio to transmit and receive data using a common antenna it easy to treat the circuits inside the duplexer as independent circuits. It is important to differentiate the frequencies where whether the Tx or Rx work on. The duplexer will only do its function without noise if there is a range of frequencies for transmission and reception that is why in each circuits there is a band pass filter that only allow certain frequencies to go through it. For the Transmitter circuit it is use a high band pass filter and for the receiver it is use a low band pass filter. The main objective of this experiments is determinate the bandwidth of these filters in order to do that and using a network analyzer certain values of cut off frequencies of the filters were determinate.In the first experiment the author connected the equipment as in Fig. 2 in order to measure insertion loss and return loss between the antenna and the transmitter, the objective was to find the cut off frequencies of the high band pass filter the values of these frequencies are in Table 1. It is important to mark that these values were measure at point where return loss had a value of -14dB and Insertion loss had a value of -3db this values of power determinate the low and the high cut off frequency of the band pass filter as it is shown on Table 1 the bandwidth for return loss and insertion loss are very similar at 31MHz and 35MHz respectively. Similarly in the second experiment were made the same measurement for insertion and return loss the difference was that for the receiver section it was use the low band pass filter, the frequency values are illustrate in Table 2. It is quite interesting how in the low band pass filter both return and insertion loss had a bandwidth of approximately 31MHZ and 35MHz the same values that the high band pass filter had.In the last experiment was measured the isolation between the transmission port and the reception port. Isolation was measured in the worst cases this means the highest frequency of the low band pass filter and the lowest frequency of the high band pass filter. It can be seem in Table 3 the values measured in these frequencies -52dB and -53dB respectively both values are low levels of powers which means that the ports are isolated.Summarizing it is possible to consider the experiments as successful due to the results obtained were standard values while working with duplexers and the condition for a proper function were complied.

CONCLUSION

The implementation of the duplexer in Base Station Radio system marked a milestone in communications development due to this device makes simple the setup of a base station a posteriori was necessary to have an antenna for transmission and an antenna for reception but with a duplexer is possible to transmit and receive with a common antenna using frequency division.A duplexer in conformed by resonance circuits and band pass filters it is important to differentiate the circuits for Tx and for Rx each circuits has a band pass filter and according to the results of the experiment it is possible to say that even though the band pass filter manage different frequencies they had the same bandwidth of approximately 35 MHz.In order for the duplexer to work properly there must be complete isolation between its ports standard values for isolation in a duplexer are up to -80dbm. In addition to that when working with this device and assuming that it is a three port device for a correct measure of insertion and return loss it is necessary to put a load of the same value of the characteristic impedance of the line and the equipment.

REFERENCES Base Station. Retrieved 07/03 2015. From Vodafone.http://www.vodafone.com/content/index/about/sustainability/mpmh/how_mobiles_work/base_stations.html Tomasi, D (2003).Sistemas de Comunicaciones Electrnicas. Phoenix, AZ. Pearson Prentice Hall.

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