App Note Antenna Measurements V1 1
Contents
1. OMICRON E LAB E Smart Measurement Solutions 3 4 Measurement of aHam Radio Antenna Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 14 of 20 Special thanks go to the members of the amateur radio station Klosterkeller Mehrerau in Bregenz Austria where we performed the measurements of two of their ham radio antennas If you want to get more information about this amateur radio station you can visit their homepage at 3 4 1 Description of the Measured Antennas Windom FD 8 160 10 meter This is a wire antenna and therefore hardly visible on the picture Smart Measurement Solutions Cushcraft R7 vertical 40 10 meter Wi ee ce reve d re ai 7 RCE wee tee pee OMICRON E LAB Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 15 of 20 3 4 2 Impedance VSWR and r Measurement Windom FD8 antenna Our first measurement using the frequency sweep mode was performed to find the carrier frequencies of the antenna We got the following result 10 40 2M 4M 6M 8M 10M 12M 14M 16M 18M 20M f Hz mum R1 Mag Reflection The carrier frequency around 7 MHz was chosen for further measurements using the external coupler mode 0 E 300 _ E 250 10 on 15 os D 3 m 20 150 O2. 25 a IJ oN 400 3 50 354 z 40 E 0 6 6M 6 8M 7 0M 7 2M 7 4M 7 6M f Hz mum TR1 Mag Reflection mm TR2 Mag Impedance oooi e ee o T 066155 MHz 20 667 dB 47 996 02 OMICRON M LAB Smart Measurement Solutions a Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 16 of 20 If you change the format settings you can display the polar smith or VSWR chart The cursor marks the frequency with the highest return loss P 90 x 75 135 45 20 0 0359 123 724 180 Frequency ee e r 066195 MHz 47 906 02 2 J42 il 1 077 10 8 i N o E L 4 9 0 i 6 6M 6 8M 7 0M 7 2M 7 4M 7 6M f Hz mum 1 R2 VSWR Reflection Result At the chosen frequency of 7 066 MHz the VSWR is 1 077 and the impedance of the antenna is 47 9 Q OMICRON as LAB Smart Measurement Solutions 7 Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 17 of 20 Cushcraft R7 antenna Beside a closer look on single carrier frequencies we can also measure the antenna characteristic over a lager frequency range The chart below shows the reflection respectively VSWR from 25 to 35 MHz of the Cushcraft R7 antenna direct measurement Two low reflection points are marked with cursors 07 5 5 a 14 10 M 15 3 O F x
3. OMICRON E LAB Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas By Stephen Synkule 2014 by OMICRON Lab V1 1 Visit www omicron lab com for more information Contact support omicron lab com for technical support Smart Measurement Solutions Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 2 of 20 Table of Contents WPS UAC ena 3 Z M as remeni TASKS cscs eens cece cegeseneccnstawesncosswesawentwesnnetsvesevesswesnnctewssewsanwesnnesswosevesswesnussss 3 3 Theory Measurement Setup amp Results cccceseeseeeeeeeseecneeeceseeceneeeonseseseesonseseeneesoaees 4 3 1 VSWR Impedance AN F cccceccceeecceeeceneceececeecceeeceuceceeeceucesueeseeessueesseeseueesseesseeessaeens 4 3 2 Direct Measurement of a Broadcast Antenna cccccceecceeeeseeeeeeeeeeeeeeeeeeseeeseeseeeseeeseeens 5 3 2 1 Description of the Measured Antenna cccccccseecceeeceeeceeecececeuseceeeseueesseeeseeesseeens 5 3 2 2 Reflection Loss amp Impedance MeasSureMen ccccceececeeeeeeeeeeeeeseeeeeeeeseeeeeeeeeaeeess 5 3 2 3 Measurement Of VOSWRANG T isisrenoineani tnni in inaa ER teenantcannesateexmeesmacnsect 8 3 2 4 Potential Problems with Direct Measurements cccccceceeeeeeeeeeeeeeeeeeeeeeseeeeseeeeaeeens 9 3 3 Broadcast Antenna Measurements with External Coupler cccccccccseeeeeseeeeeeeeeeeeeees 10 3 3 1 Measurement setu
4. 20 JJ am c NO 25 e 304 E H 35 E z 40 L 0 25M 26M 27M 28M 29M 30M 31M 32M 33M 34M 35M f Hz mum R1 Mag Reflection mmm TR2 VSWR Reflection 20 950 MHz 20 145 dE 1 218 32 450 MHz 16 054 dB 1 374 3 500 MHz 4 091 dE 155 759 m S l mum R2 Reflection OMICRON Rs LAB a Smart Measurement Solutions Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 18 of 20 4 Conclusion The Bode 100 offers all necessary tools to perform measurements on short medium and long wave antennas All important parameters as impedance reflection coefficient or Voltage Standing Wave Ratio VSWR can be measured and displayed easily The Bode Analyzer Suite offers all graphical possibilities to display Smith Charts linear and logarithmic axis scaling or polar plots of results Appendix Guideline for the use of External Amplifiers To avoid damage it is important that the maximum allowed input power applied to the Bode 100 is not exceeded at any point of the measurement Before an amplifier can be used the maximum input ratings for both receivers have to be considered to avoid damaging the Bode 100 It is also important to avoid overload during the measurements The input of the Bode 100 is displayed in the following figure Input Analog Attenuator Digital
5. Mode Bl El Calculation of the attenuator settings using the measurement results gathered from the first measurements The gain of the amplifier we used is 38 dB Our coupler has a 25 dB loss for its coupled port and a 25 dB loss for the reflected port Therefore the signal at the inputs CH1 amp CH2 is 13 dB higher than the output level of the Bode 100 Antenna OUTPUT __ Q Bode 100 Transmitted l 0 15 dB Amplifier Directional Coupler To achieve an optimum noise rejection we use the highest possible output level for our measurement To choose this level we have to consider the maximum allowed input power for CH1 amp CH2 P max 50 Q input impedance 30 dBm and the overload condition for these channels see Appendix Pou Pout Gaingmpi coupler 13 dBm 13 dBm 26 dBm This calculation shows that we are within the maximum input power range The attenuators for CH1 amp CH2 need to be set to 40 dB to avoid overloading the channels see attenuator table in the Appendix OMICRON E LAB Smart Measurement Solutions a Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 12 of 20 For the impedance amp reflection loss measurement we applied the following settings in the external coupler mode Start Frequency Stop Frequency Attenuator CH1 amp CH2 Receiver Bandwidth Level Number of points Sweep mode Trace 1 O O O OO0O OOO o Trace 2 0
6. of use guarantee trouble free operation Close customer relationship and more than 25 years in house experience enable the development of innovative products close to the field Europe Middle East Africa Asia Pacific Americas OMICRON electronics GmbH OMICRON electronics Asia Limited OMICRON electronics Corp USA Phone 43 59495 Phone 852 3767 5500 Phone 1 713 830 4660 Fax 43 59495 9999 Fax 852 3767 5400 Fax 1 713 830 4661 info omicron lab com Mm www omicron lab com
7. 5 MHz 2 0 MHz 40 dB 300 Hz 13 dBm 201 or more linear Measurement Reflection Format Mag dB Measurement Impedance Format Mag Connect your directional coupler and the required cables to the Bode 100 and perform a User Calibration for OPEN SHORT and LOAD at the port where you connect the antenna Attention The maximum input power for the delivered 50 load resistor is 1 W To avoid damaging the 50 Q calibration load use a lower output level during calibration Start a frequency sweep to measure reflection coefficient and impedance of the antenna 10 TR1 dB 20 30 40 l l l l 0 6M 0 8M 1 0M mum R1 Mag Reflection 1 2M 1 4M 1 6M 1 8M 2 0M f Hz OMICRON N LAB Smart Measurement Solutions 7 Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 13 of 20 10007 TR2 Ohm 0 6M 0 8M 1 0M 1 2M 1 4M 1 6M 1 8M 2 0M f Hz mum R2 Mag Impedance For the reflection measurement switch the traces to e Trace 1 Measurement Reflection Format Polar or Smith e Trace 2 Measurement Reflection Format VSWR 180 mums R1 Reflection mums TR1 Reflection 1007 80 60 TR2 404 20 0 6M 0 8M 1 0M 1 2M 1 4M 1 6M 1 8M 2 0M t Hz mum R2 VSWR Reflection
8. B AW dB 5 p R In the following we did summarize the important points which need to be considered when using the Bode 100 in combination with an external amplifier and an external coupler Important points e Overcharge The maximum allowed input power for the 50 Q input impedance is 30 dBm Using signals with more power will damage the Bode 100 e Overload To avoid measurement failures the input voltage is limited by the overload range of the ADC and the chosen attenuator settings e Tolerances Always consider a possibly higher gain than specified of your amplifier due to its tolerances OMICRON E LAB Smart Measurement Solutions 7 Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 20 of 20 IF DE METT i E ah 1 5 OMICRON Lab is a division of OMICRON electronics specialized in providing Smart Measurement Solutions to professionals such as scientists engineers and teachers engaged in the field of electronics It simplifies measurement tasks and provides its customers with more time to focus on their real business OMICRON Lab was established in 2006 and is meanwhile serving customers in more than 40 countries Offices in America Europe East Asia and an international network of distributors enable a fast and extraordinary customer support OMICRON Lab products stand for high quality offered at the best price value ratio on the market The products reliability and ease
9. e picture below shows a spectrum analyzer record of the signals we received over the measured broadcast antenna lf the signal received by the antenna is large enough it could damage the Bode 100 OMICRON E LAB Smart Measurement Solutions a Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 10 of 20 3 3 Broadcast Antenna Measurements with External Coupler 3 3 1 Measurement setup To avoid potential problems that come with direct antenna measurements the Bode 100 offers a measurement mode which allows the use of an external directional coupler in combination with an external amplifier The measurement setup for this mode is shown below Antenna OUTPUT __ INPUT Transmitted Forward Reflected Amplifier Directional Coupler The Bode 100 output is connected to the amplifier input the amplifier s output to the input port of the direction coupler the forward port to CH1 as reference signal the reflected port to CH2 and the antenna to the transmitted port ATTENTION To avoid damaging the Bode 100 please read the Appendix of this document before using an external amplifier OMICRON E LAB E Smart Measurement Solutions Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 11 of 20 The following measurements were performed in the external coupler mode A Hy 3 3 2 Impedance VSWR and r Measurement in the External Coupler
10. his shows that the antenna is not perfectly matched at the carrier frequency of 1 026 MHz Hint You can export your measurement data for further calculations in other software using the csv coma separated value export function of the Bode 100 Export Traces Data OMICRON E LAB E Smart Measurement Solutions Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 8 of 20 3 2 3 Measurement of VSWR and r To display the VSWR and ryou can keep your impedance measurement and apply the following new settings for Trace 1 amp 2 o Trace 1 Measurement Reflection Format Polar o Trace 2 Measurement Reflection Format VSWR 135 4 180 0 135 45 E R1 Reflection 80 70 60 50 40 30 20 10 TR2 0 6M 0 8M 1 0M 1 2M 1 4M f Hz mum R2 VSWR Reflection OMICRON E LAB Smart Measurement Solutions a Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 9 of 20 3 2 4 Potential Problems with Direct Measurements For some measurements the Bode 100 maximum output level of 20 mW 13 dBm may not be sufficient this could result in noisy curves as shown in the graph below TR1 dB 1 0 1 5 2 0 2 5 3 0 3 5 f MHz TR1 Mag Reflection Furthermore the measured antenna could receive distortions and signals from other transmitters Th
11. lt 100mV Converter The absolute maximum ratings for the Bode 100 Channel 1 and Channel 2 inputs 500hm input impedance are defined as follows Maximum input power 1W Maximum input voltage 7 Vims The maximum allowed input power in dBm can be calculated as follows P 1W Pmax dpm 10 log a 10 log gt 30 dBm OMICRON E LAB Smart Measurement Solutions 7 Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 19 of 20 Example If you plan to measure the gain of a 37dB amplifier you will have to keep the Bode 100 source signal the input signal of the amplifier at least below 7dBm to avoid damaging the inputs Psourcemax max dBm Gainamp ab 30 dBm 37 dB 7 dBm The maximum input voltage to avoid an overload of Chi amp Ch2 which would result in measurement failures is defined by the maximum input voltage of the internal ADC and the chosen attenuator settings Input sensitivity 100 mV full scale for input attenuator 0 dB Attenuator 0 10 Vi 1008 0 316 Vin 20 dB 13 dBm 30 dB 23 dBm 3 16 Vims 40 dB 33 dBm 10 0 Vims Example Let s say we use the same amplifier as before We have to keep the Bode 100 source level below 14 dB for an attenuator adjustment of 30 dB to avoid an overload l reena PcHmax dBm Gainamp aB 23 dBm 37 dBm 14 dBm The following formulas were used for the calculations AVapy 20 lo 2 dB AP 10 lo 2 P d
12. lude possible problems for the input channels of the Bode 100 OMICRON E LAB Smart Measurement Solutions a Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 6 of 20 To measure the impedance of the antenna we switch to the frequency sweep mode In the frequency sweep mode the following settings were applied o Start Frequency 0 5 MHz o Stop Frequency 1 5 MHz o Attenuators 20 dB o Reference internal o Receiver Bandwidth 300 Hz o Level 13 dBm o Number of points 401 or more o Sweep mode linear o Trace 1 Measurement Reflection Format Mag dB o Trace 2 Measurement Impedance Format Mag OPEN SHORT and LOAD calibration was performed to remove the influence of the connection cable The antenna was connected to the Bode 100 as shown in the pictures below OMICRON E LAB Smart Measurement Solutions a Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 7 of 20 Starting a frequency sweep leads to reflection and impedance of the antenna 10 10 TR1 dB 20 30 40 0 6M 0 8M 1 0M 1 2M 1 4M f Hz mum R1 Mag Reflection 1000 800 OD TR2 Ohm 0 6M 0 8M 1 0M 1 2M 1 4M t Hz mum 1 R2 Mag Impedance Result We measured a minimum reflection of 34 dB at 1 020 MHz which equals an impedance of 51 98 T
13. nnas Page 4 of 20 3 Theory Measurement Setup amp Results 3 1 VSWR Impedance and r The Bode 100 directly measures the complex impedance Z by analyzing the forward and reflected wave The reflection coefficient rand the resulting VSWR are than calculated from the measured Z and the reference resistance Ro using the following relations oe pee me cad oI T Z Re 1 r V voltage at the reference plane r reflection coefficient l current at the reference plane VSWR Voltage Standing Wave Ratio Z lmpedance Ro reference resistance Measurement Note The reference resistance Ao can be set in the Reference Resistance 50 00 Measurement area The reference resistance is used for the calculation of the reflection coefficient and therefore influences the VSWR result as well The Bode Analyzer Suite enables you to change the reference resistance in the range from 1 Q 1 KO This allows calculating the VSWR and ralso for systems with an Ro 50 Q Example The center of the Smith chart indicates the point with ideal matching r 0 Reflection Ro 50 Q Reflection Ro 75 Q any iy N ol _ 2 oO i yi N Xi Y gt ve PS Se 7 we att 100 mm 7 R2 Reflection mum R2 Reflection The charts above show a measurement of the same filter terminated with 50 Q The left chart was calculated for Ro 50 Q while the right one
14. ntenna parameters are measured with the following two measurement methods supported by the Bode 100 e Direct Impedance Reflection VSWR measurement in the frequency sweep mode e Impedance Reflection VSWR Measurement with increased output power using an external power amplifier and an external directional coupler In the appendix of this document you will find a summary on things to consider when you use external directional couplers and amplifiers in combination with the Bode 100 2 Measurement Tasks To avoid reflections and to ensure that the maximum broadcast power is achieved the impedance of a broadcast or Ham Radio antenna needs to match the impedance of the connected signal source The Voltage Standing Wave Ratio VSWR and the reflection factor r are two internationally used parameters to qualify how well an antenna matches its reference resistance By analyzing a medium wave broadcast antenna as well as a two different Ham radio antennas the following topics are covered e Some theory about the relationship between impedance VSWR and r e Direct Impedance VSWR r measurement with the Bode 100 e What problems can arise when antennas are measured e The advantages of Impedance VSWR r measurements using the external coupler mode of the Bode 100 e Appendix Using amplifiers with the Bode 100 OMICRON E LAB Smart Measurement Solutions 7 Bode 100 Application Note Evaluation of Broadcast and Ham Radio Ante
15. p ivory cds orstouns aren ora dares ori ieenhesiheannenndicnnhihad cendutahicendiaddceihcba diced suadiceisetanti 10 3 3 2 Impedance VSWR and r Measurement in the External Coupler Mode 11 3 4 Measurement of a Ham Radio Antenna c cccccseccceeeccecececcceeeceuseseeeceucesueeseeesseeensess 14 3 4 1 Description of the Measured Antennas ccccccccseeeceeeeeeeeseeeeseeeeseseueeseeesaeeesaees 14 3 4 2 Impedance VSWR and rMeaSureMe nt ccceccceececeeecceeeceeeeceeecsueeceeeaueessesenaess 15 4 CONCUSSION gece seccecrcarcete cece seria wire cca mca ere encanta ved encanta dencleamesien out nleacientereneneb lesteutencwencs 18 Note Basic procedures such as setting up adjusting and calibrating the Bode 100 are described In the Bode 100 user manual You can download the Bode 100 user manual at www omicron lab com bode 100 downloads 3 Note All measurements in this application note have been performed with the Bode Analyzer Suite V2 43 Use this version or a higher version to perform the measurements shown in this document You can download the latest version at www omicron lab com bode 100 downloads OMICRON E LAB Smart Measurement Solutions 7 Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 3 of 20 1 Abstract This application note explains how to measure the impedance reflection factor and VSWR of broadcast antennas as well as Ham Radio Antennas These a
16. shows the results for R 75 Q OMICRON E LAB Smart Measurement Solutions a Bode 100 Application Note Evaluation of Broadcast and Ham Radio Antennas Page 5 of 20 It is important to minimize reflected signals to maximize the power radiated by the antenna The optimum efficiency of a broadcast antenna is reached when the impedance of the antenna exactly matches the source resistance reference resistance Ro The reflection coefficient ris defined in the range from 1 to 1 and the VSWR parameter in the range from 1 for ideal matching with r 0 to infinite 3 2 Direct Measurement of a Broadcast Antenna 3 2 1 Description of the Measured Antenna All measurements described in this chapter where performed on a medium wave transmission site which was not in use at the time this document was written The measured broadcast antenna has the following characteristics e The antenna aerial has a triangular cross section and an omni directional vertically polarized antenna pattern e The antenna height length is 50 meters e The electrical length of the antenna is defined by its roof capacitance and a coil which is connected in series to the antenna e The electrical antenna length was optimized for an AM medium wave signal with a carrier frequency of 1 026 MHz 3 2 2 Reflection Loss amp Impedance Measurement Before we started our measurements we used a spectrum analyzer to check the signal received by the antenna to exc
Download Pdf Manuals
Related Search