Magnetic loop controller. It can be either directly connected to a radio by transmissibility of magnetic levitation system with inner PID loop controlling the magnetic levitation support. Please visit my YouTube channel to see this project in action Oct 19, 2012 · This video by Ricardo Caratti demonstrates his method for controlling a Magnetic Loop antenna with an Arduino. The HG3 Stepper tuned Magnetic Loop Antenna delivers unprecedented capability, performance and convenience. 5 ft in circumference and 23% efficient at 10. The tuning is done with a high voltage capacitor in the loop, which is made from aluminium tubing. Magnetic Loop - Software September 2015 The Loop is working fine, but two things are bothering me. To solve problem 1. Retevis Ailunce HD2 ISRU Frequency Expansion March 26, 2024; N9SAB Antenna Care Package Unboxing March 24 Aug 28, 2023 · 5 320 UAH. 8V stepper and the L298N H-Bridge controller. Too much 'L'. Apr 11, 2020 · This is a magnetic loop controller board designed by Loftur TF3LJ and VE2LJX. tuning is critical, as Eham reviews show the main dfficulty is getting the SWR properly dipped. Magnetic loop antennas typically have a small negative gain when compared to a dipole. MagLoop, Founder & Owner. A magnetic loop antenna is basically an oversized inductor, brought into resonance with an (adjustable) capacitor. sh123 / magloop_controller. It remotely controls both the HG3 PRO and QRO Magnetic Loop Antennas and the AR1 Rotator. The amplifier board converts a command signal from the DSP to drive a control current through the AMB actuator coils. The Magnetic Loop Controller tunes theantenna in real time, tracking every movement of the Transceiver VFO. Click here to see a video that shows the box example project with the Android and Arduino Antenna Tuner . This unstable attitude of Active Magnetic Bearing and its built-in nonlinearities make the designing and control problems really challenging. The capacitor is wired with both sections in series making it 250pF in total. If the inductor has a circumference of much less than, say, 1/10th of a wavelength, then the efficiency of the antenna will suffer. Professionals all over the world use Magnetic AutoControl toll, parking, and access barriers for a variety of applications. Mar 5, 2012 · DIY Magnetic Loop Antenna – Part 2. Remove the magnetic loop antenna and connect a dummy in its place. The diameter of the conductor determines its resistance and Then cut the power. manually operated Test mode gamma match. Precise position, speed and torque control. Ideally, this control should be located below the large loop rather than within its circumference. MagLoop Tuner does exactly that, by having a set of calibrated values and estimating the variable capacitor position for each frequency change. Motorised Tuning & Loop Capacitor Remote Hand Controller. It tested ok up to 700 volts which makes it ideal for 5-10w QRP transmitters. Accompanied by a detailed description, the 6-foot loop features a built-in stepper motor control circuit, while the 12-foot loop incorporates a separate loop controller. Retaining all Aug 31, 2020 · W7BV Rating: 2020-09-05; Excellent Remotely Tuned Mag Loop Antenna Time Owned: 0 to 3 months. Net language, it can run on any operating system that provides a . Motor control and homing. It's currently quite difficult to tune the antenna, especially on the 20m band. However, the DC motor control could be improved by adding a PWM-driven "fine tune" mode. The antenna’s tuning capacitor is adjusted using a stepper motor interfaced with the Arduino equipped to read IR commands sent from a compatible IR remote control. I built a Magnetic Loop Antenna, and my idea was to control the tuning capacitor remotely. 3 Nm. Sep 3, 2019 · I intend to build a QRP magnetic loop and this ahort video clip shows the components to adjust the 30pF to 1000pF variable capacitor. This control is accomplished by pulling the microparticles using the magnetic field gradients towards the reference position *** NOW with support for Variable Vacuum Capacitors ***New WiFi Stepper Motor Controller App for Magnetic Loop Antenna that is replacing the Blynk App! (as B Feb 18, 2012 · It is worth changing the loop size in the calculator to get the best efficiency possible in your favorite band. Jun 14, 2015 · A magnetic microrobot was actuated up to 6 mm/s with position accuracy of 6 µm or better using vision-based closed-loop control (Fig. Low costs, versatile functions, exceptional durability – use vehicle barriers from Magnetic for access control, parking and toll collection! The loop is a continuous run of wire that enters and exits from the same point. The characteristic equation of the closed-loop system in Figure 13 can be used for the purpose of ¯nding Kp, Ki,andKd such that the desired performance speci¯cations are achieved. system, which utilized superimposed magnetic fields from a number of electromag-netic coils to generate gradients of more than 2T=m. Although still in prototyping phase, I think this is absolutely brilliant. A rotary encoder is used to manually tune the capacitor but when SWR Bridge is selected from the Main Jan 30, 2019 · I am starting to work on the automatic tuner for the magnetic loop antenna. and then change one step and measure SWR. The VVC cost about US$190 and postage to VK was about half that again! NOTE: In this project, you will find a new WiFi Stepper Motor Controller App for Magnetic Loop Antenna, that is replacing the old Blynk App (as Blynk upgraded to v2 and removed v1 from the AppStore and the PlayStore). Rated 5. 0. When using the remote control, total maximum tuning time from 7. 1Mhz but 91% efficient at 28Mhz. The software is a single GUI application, written in C#, that handles the control loop and motor management. We used it on Field Day this year and also have logged over 10,000 WSPR contacts with it. I wrote a piece of VB code that interfaced with HDSDR to get the VFO and send the appropriate stepper position to the Arduino via TCP. However, their signal to noise ratio far exceeds that of a dipole. We offer a wide variety of barrier booms and equipping variants for the optimum function and visibility of Magnetic-barrier systems. To associate your repository with the magnetic-loop topic, visit your repo's landing page and select "manage topics. The heart of the controller is the ESP32 microcontroller. 60 out of 5 based on 5 customer ratings. Midway through building my version of Loftur Jónasson – TF3LJ / VE2LJX‘s Automatic Loop Controller, I … Continue reading "Antenna tuning by stealth" The 3-foot-wide base Alpha Loop that covers 10 to 40 Meters is remotely tuned and rated at 100 watts PEP SSB, 50 watts CW, or 25 watts digital, which are each based on duty cycles. This prot The control program in the DSP also handles levitation logic, fault and trend monitoring and diagnostic functions. #4. I will implement the various functional blocks in the following order: 1. There is one via under the stepper driver which could be a little bigger, but I was driving 2 amps to a stepper motor without an issue. 5 and again SWR<2 (rising) it calculate the middle position and move the motor there. As the name implies, ham radio relies on antennas to function, and most designs can To associate your repository with the magnetic-loop-controller topic, visit your repo's landing page and select "manage topics. It converts the eld strength into a voltage signal which is compared with a reference value. (M5 type 5-5. SKU Loop_Tuner Category Alpha Matches Tags Accessories by Alpha Antenna, Alpha Match, Remote tuning kit for the Alpha Magnetic Loop MagLoop. It enables monitoring of two induction loops, ensures secure integration in the overall system, and prevents the barrier's boom from closing on a vehicle. 00. This project uses the Arduino core libraries. I used an Arduino UNO with an ethernet shield to control the 25 turn vacuum variable capacitor. A system for precise control of Variable Vacuum Capacitors and most modern Amateur transceivers. Closed-loop control also improves the actuation Closed-loop control of magnetic elds for atomic physics experiments 3 3. Thank You & 73 VE3UK, W. A simple but efficient way to easily control a Magnetic Loop Antenna. AMA Magnetic Loops - Principle of construction. For better water protection, the HG-1 motor drive assembly may be mounted facing down. I am using his original PCB version from June 2014 which indicates how long I have been intending to build this device! Description. 5-200S-333 Vacuum Variable Capacitor, 10-205pf, 7. I used open hardware from various sites to make my life easy. 4. A 12 Volt 5 rpm DC moto Make sure the HG-1 Magnetic Loop antenna is placed in an obstruction free area. Mag Loop 20-15m. More info Tuning a magnetic loop ON6YC More test. Cut New hole Link. You can assemble the main loop from continuous copper tube or from eight straight sections and 45 degree This works for receivers and transceivers. In order to more easily develop the loop tuner rmware/software, I built a magnetic loop simulator. 2-1. A flimsy and rather poorly made plastic cover protects the tuning capacitor and its motor and the coupling Mar 18, 2022 · I just wired up my MFJ-1786 magnetic loop, which hasn't been used for years. the loop has to be made smaller. The only interface required is a small box with two DC female connectors. In this study, we demonstrate the wireless magnetic-based motion control of paramagnetic microparticles using ultrasound feedback. Meanwhile, a double closed-loop control strategy is utilized to eliminate the resonance introduced by the LCL filter and stabilize the system. Figure 2 describes the basic operation of the magnetic bearing control loop. This magnetic loop antenna is a complete circuit, so there is no need for radials or counterpoise. ZKTime Web 2. 431-071 555 Timer PCB. Tuning a magnetic loop antenna takes some time. I decided the MFJ-1788 was appropriate as the 40M through 15M bands were most desirable for me, and I could operate QRP to 100 watts with my Yaesu FT-857D transceiver. Slow Fast. After using the new HG-3 Stepper Tuner and Mag Loop, Pro Controller, and AR-1 Rotator with the new aluminum mast for the past two months, I am very impressed with the new tuner and controller, especially the auto tune feature. Out of stock. The all inside a mouse small magnetic loop control concept is a more practical and elegant solution. Chapter 4: Automating Magnetic Loop Antenna (Part 1) So far, we have discussed the good and bad points of MLA. To enable automatic closed-loop motion control of magnetic agents, a position feedback system is required. MFJs tiny 36 inch diameter loop antenna lets you operate 15 through 40 Meters continuously -- including the WARC bands! Ideal for limited space -- apartments, small lots, motor homes, attics, or mobile homes. This allows the tuning capacitor to rotate clockwise and Magnetic loop antennas are relatively small, their circumference is usually between 1/10th and 1/4th of a wavelength. Since then he has been building custom magnetic loops for both amateur use as well as non amateur Nov 20, 2019 · Share experiences and designs of magnetic loop controllers. Add a description, image, and links to the magnetic-loop topic page so that developers can more easily learn about it. Jun 14, 2015 · 15 Youtube Video of the Controller: 16 To build a 24 foot Magnetic Loop: A Magnetic Loop Antenna is basically just a resonant circuit using an oversized inductor and an adjustable capacitor. Apr 9, 2014 · The Control Software The main component of the system is the PC-based software. The system stability will be improved and a safety enclosure will be used. In Stock! The HG3 Pro currently has a 1 to 2 week lead time. #5. Tuner for magnetic loop antennas. Some scholars have proposed dual-axis [28] and triaxial magnetic field closed-loop control systems [29]. It also includes a direct wire remote control. Jan 2, 2011 · Magnetic Loop Controller. Tuning does not require transmitting! Magnetic loop antennas typically have a small negative gain when compared to a dipole. 6) [76]. It employs a proven, accurate and repeatable stepper motor design. SF420. cinosh07 / VA2SAJ-Magnetic-Loop-Controller Public. (Bob) Leschyna. Figure 1 mag loop, the capacitors C1&C2 resonate the loop and equally share the high voltage produced as a result of the loop’s high “Q”, but at the expense of reducing the effective tuning capacitance by a 1/2. The author's firmware for the antenna controller was developed in the Arduino IDE. ; images folder has some pictures about this project. ( 2 customer reviews) $ 1,335. Magnetic loop controller - Easydriver & L298N. Go to that position very first. The current system uses a method of a passive rotary inductrack and Halbach array of magnets to generate magnetic levitation. Each factory made 5 boards (minimum order quantity). The idea of having a big Loop, on a sturdy tripod, outside of the Magnetic Loop Antennas are cool for size constraints, but suffer from low bandwidth. Also, the varicap I used has a 24V DC motor. The meter lit up, but pressing the loop buttons had virtually no effect. Ham radio allows for the broadcast and reception of non-commercial radio signals across vast distances with relatively inexpensive equipment. The PSA-03 wire is connected to PSA-02 with a section of 1 sq. Although it offers the means to control the particles, it also poses difficulties: the magnetic field is applied uniformly subsystem with the PID controller is shown in Figure 13. PSA-02 - induction (magnetic) loop controller. Description. The amber lights flicked slightly, but they were not so bright as I remember them, and the motor didn't turn. His solution is an elegant one, he’s made a remote retuning setup using a stepper motor, an Arduino, and a 1 Mounting vacuum variable capacitor to main loop. R. Tuning the Magnetic loop antenna, by controling the capacitor remotely, using Wifi. ZKB106/ZKB108. Inner loop combine Gamma match test Gamma Relais Design a controller to achieve closed loop control of displacement height Implement the controller using a microcontroller Planning LML’s objective is to achieve closed-loop control of the magnetic levitation height of the Halbach Array of magnets. This is with the tuning speed knob is turned completely to the right for maximum tuning speed. Efficiency, tuning ranges, and the innovative autotuning solution using a Barrier booms. Make a note on whether your magnetic antenna loop is either tuning up or down when pressing either the green or red button. Restore the connections on the directional coupler to their original state. This was set up to control my magnetic loop antenna using a 2. 0 across the entire band. e b c. 10. Using the Automatic Mag Loop Controller a) Automatic Tuning a Butterfly Capacitor If you are using the controller with a butterfly antenna that's free to rotate 360 degrees, tuning up is very easy. Unfortunately the loop can't be tuned to 40m. Magnetic loops are great for the ham who has limited space on the lower bands. Magnetic gate openers provide a safe, secure barrier for access control needs, from government facilities, highways, and universities to private businesses, shopping malls, and sporting facilities. But due to its high Q in nature, the effective bandwidth is very narrow, not much more than 10~20KHz even at a relatively higher band. Connect both ends of the supplied cable (common Ethernet cable) to the motor assembly and . " GitHub is where people build software. The only communciations that you will receive from me will be pertaining to my Magnetic Loop Antennas. The PID controller calculates the di erence between Mar 1, 2024 · The schematic and physical drawings of the experimental setup for the magnetic field closed-loop control system of the single-beam SERF atomic magnetometer are shown in Fig. A new MFJ-1788, however, was cost-prohibitive. The ATU 2. Having the tuning knob on top also would allow dirt and water to enter the housing. Feb 25, 2002 · This is a controller for 4 small magnetic loops with arduino uno and a cnc shield - GitHub - cabrinana2/Control-for-4-magnetic-loops: This is a controller for 4 small magnetic loops with arduino u Nevertheless, for such a small antenna the magnetic loop's performance is nothing short of excellent. The designation of PID-surface SMC reduces the chattering phenomenon in conventional SMC. It can be used to build a tuner box by using a 3D printer. Remote Tuning tips. Component Selection: Rated 4. Most of you know that next winter I’ll be operating for the most part, out of a tipi tent. 5kv Peak, Energy Labs from RF Parts. Arduino Team — April 14th, 2023. 3. This PCB was designed by 9A3GOS (me) and assembled by two assembly factories. IN = 12 VDC input. Jul 30, 2017 · It’s a prototype of an upcoming product called CHA URT, or Universal Remote. Most magnetic loops have the capacitor at the top of the main loop and the gamma match or matching loop at the bottom, this arrangement avoids running the feed-line through the center of the antenna. More than 100 million people use GitHub to discover, fork, and contribute to over 420 million projects. Seeking algorithm to store history and tune quickly. . Placing a hand on or near to the knob to adjust it, affects the tuning of the antenna. The controller uses a very low-power DDS oscillator to tune the loop so it will tune right through your amplifier. Jul 30, 2017 · New magnetic loop controller from Chameleon. This makes this type of antenna very attractive to many radio amateurs with little space for aerials. From the 3 point of SWR<2 (falling), SWR<1. Due to their high torque at low speeds, closed-loop stepper motors are especially well-suited for direct drives. Vehicle barriers that set standards. Get both low angle radiation for excellent DX and high angle radiation for Nov 21, 2019 · Al and I have also designed an automatic remote controller for our "Luggable Double-Double" mag loop. This is an ESP32-based controller remote for a magnetic loop antenna on HF frequencies. There are two Nanotec offers integrated stepper motors in four sizes and with a holding torque of up to 9. Designed by G8ODE Aug 2011 iss 1. The main feature of a magnetic loop is it's comparably small size in relation to the wavelength. Feb 26, 2009 · This device remotely adjust a super light small magnetic loop antenna, that can be used at home on the balcony or during my QRP pedestrian operations when th closed loop control of the magnetic levitation height. mm. It is a small, easily set up (if somewhat hard to build), and surprisingly effective antenna. $ 299. 2. Notifications Fork 2; Star 6. # WS2812 5050 RGB Strip for motor speed indication. Magnetic loop controller – home stretch After a long break I have finally got back to completing the Magnetic Loop Controller designed by Loftur Jonasson that I started almost two years ago now. 56R. There is no difficult tuning process, no note taking or complicated search for lowest SWR. May 31, 2014 · Controlling the motion of microrobots based on feedback provided using an imaging modality is essential to make them clinically viable. Set the voltmeter to read a negative voltage. SWR measurement. Closed-loop magnetometer systems are promising to advance The Alpha Loop tuning knob is located on the top of the tuner housing. The MagLoop brand of Magnetic Loops was founded by Bob VE3UK in 2005. Get both low angle radiation for excellent DX and high angel radiation In fact, it really was surprising how easy. The proof of concept is to drive the ILI9341 display and show the "Splash" screen which is shown at the start-up of the controller. The simulation results prove the high quality Mar 1, 2024 · This in-situ measurement and feedback control of magnetic field disturbances not only enhances measurement stability but also improves metrics such as bandwidth and dynamic range. 7MHz is 90 seconds. Loop Antenna & Automatic Magnetic Loop Controller Handmade loop For 2 & 1 Meter Loop Test Mode inner loop Coax. C3 provides the matching of the loop’s low impedance to the transceiver’s 50Ω. ZK SmartKey. Since then he has been building custom magnetic loops for both amateur use as well as non amateur Sep 1, 2018 · The magnetic forces are generated by feedback loop control. The detector powers the loop causing a magnetic field in the loop area. MFJs tiny 36 inch diameter loop antenna lets you operate 10 through 30 MHz continuously -- including the WARC bands! Ideal for limited space -- apartments, small lots, motor homes, attics, or mobile homes. Apr 5, 2017 · In response to a viewer request for more detailed info on my remote tuning solution. Just a quick board to connect the Nano with the Easydriver. Section 5 shows the experimental results of the magnetic levitation system with double closed-loop PID control, and conclusion are drawn in Section 6. Homemade - VA2SAJ Fully Automatic Tuner for ham radio magnetic loop antenna. Designed to determine whether the car in front of the barrier. An automatic tuner could solve that problem by re-tuning the antenna whenever the frequency is changed on the radio. 6) is also included to account for the iss term Explore two magnetic loop antenna constructions, utilizing a 6-foot and a 12-foot square loop. This also uses a Nema 17 stepper motor to drive a small variable capacitor via a worm gear and gives a reduction ratio of 20:1 so similar to the real magnetic loop antenna. ZK1510 Series. The components The closed-loop control system starts with the sensor which detects the magnetic eld strength along one axis. Active Magnetic Bearing (AMB) is a highly nonlinear and unstable system. Unfortunately, it looked like the loop controller had gone U/S. 3. Mag Loop Controller. Included: Dec 16, 2023 · It is recommended that the space between the stator plates that we will lay against each other should be a 5mm or 6mm gap in order to avoid arcing at high voltage. This represents a difference of about 6dB or 1 S-Unit. Section 4 is the simulation of the system with double closed-loop PID. I ordered an EL7. OUT = PWM DC low speed voltage or 12 VDC voltage selected by the mouse buttons. 5. The loop antenna will still tune properly. Magnetic single-turn absolute encoder or battery-free multi-turn absolute encoder (PD4 E Apr 17, 2021 · The New HG3plus controller was completely redesigned. Apr 14, 2023 · Building an experimental magnetic loop antenna with a stepper motor and an Arduino. In other words, unlike other magnetic transmitting loop antennacontrollers, there is no need to transmit and re-tune for minimumSWR every time the frequency has been changed. Recent Posts. The loop is designed for a type of vacuum variable capacitor with mounting holes at each end. Shown in Figure 9 is the top level system block diagram of the closed loop feedback. Replacement magnetic loop control unit by G4CNH Having been given an ISOLOOP magnetic loop antenna, without a control box, I started a search on the internet for some ideas, well at least a circuit diagram of the missing LC-2 control unit for a start. Remote tuning kit for the Alpha Magnetic Loop MagLoop. Turn the HG-1 Remote Tuner on; the green SBY LED should illuminate. It is best to obtain regular–sized aluminum spacer parts. 0MHz to 29. Simple Remote Tuning Control for HF Mag Loops – G8ODE. My practical skills of stepper motors being virtually zero and AEA who made the ISOLOOP went out A magnetic loop can work well if it has two qualities: enough power handling (a 5 kV vacuum variable will handle 100 Watts, 15kV will do a kW); and a decent remote tuning setup. The system runs under Linux on a Raspberry Pi 3. The MFJ magnetic loops are about 36 inches in diameter, made of aluminium, which is welded to the tuning capacitor to minimize losses. May 9, 2017 · [Oleg Borisov, RL5D] has a magnetic loop, and soon tired of the constant retuning. 1 mm bore and 5mm or 6mm wide) Alternatively you can use M5 4-6mm wide (~1/4″) nuts. Figure 1. 00 out of 5 based on 2 customer ratings. Modifying the RS Stock No. For example, my 30-10 Meter loop is 8. It works on 40-30-20M with an SWR typically less than 1. [12,13] This system was used to propel microrobots by using an open-loop control system. The alkali gas cell is heated and stabilized at 120 °C using the non-magnetic electrical heating technique. 1- The loop was calculated to have a range from 160 to 40 meter. Set the controller to the MAN / SLOW modes, and connect your voltmeter to controller's ALC output lead and ground. Aug 4, 2016 · One of the most important documents for anyone who wants to know what makes a magnetic loop tick is Leigh Turner VK5KLT’s “An Overview of the Underestimated Magnetic Loop HF Antenna” which can be found on his club website. A TB6600 stepper driver is used to drive a stepper motor to rotate either a butterfly, or vacuum variable capacitor. A natural candidate for powering as well as tracking these magnetic particles is the MRI scanner. Building such a magnetic loop yourself costs around 200 bucks, whereas a commercial solution costs at least 500 USD. Set the CW mode. It searches in the EEPROM from base position of that band (this data is entered manually in initialization) #3. 0 display shows frequency and SWR immediately and LEDs signal the status of the controller and the STEALTH LOOP. . But how do they perform?In this Ask an Elmer segment we find out!Hand carried Control of multiple magnetic particles inside the human body may have many potential applications, such as drug delivery in places where conventional procedures cannot reach. I built a transmitting magnetic loop several years ago. Step 4: Magnetic Loop Simulator. Tuning capacitor is a 500+500pF from an old valve receiver, obtained for £2 on the second hand market. In this paper, a closed loop current controller for an active magnetic bearing (AMB) is designed to hover a ferromagnetic material at a particular air gap (10mm). The control box schematic can be downloaded from my channel's Facebook pa Magnetic AutoControl 2-Channel Loop Detector Module (Installed) - DM02 This 2-channel loop detector is plugged directly into the MGC controller. Dec 16, 2021 · With the magnetic coupling influence taken into consideration, more effective design principles of the filter are discussed according to theoretical analysis and mathematical modeling. 2- The tuning with a DC motor and some up and down buttons is a hassle. Enjoy both DX and local contacts mounted vertically. In addition, when the motor terminal voltage reaches the maximum output voltage of the driver, the Saved searches Use saved searches to filter your results more quickly This is the repository for a magnetic loop antenna controller which is patterned after a design published in the book "Microcontroller Projects for Amateur Radio" by Jack Purdum W8TEE and Albert Peter AC8GY. controller. Since the software is written using a . Net runtime with Forms support. Jun 1, 2021 · So looking at the magnetic loop controller, how to translate from the "Blue Pill", to the "Pi Pico"? I decided to work on a "proof of concept". I soon discovered the MFJ-1786 and MFJ-1788 mag loop antennas were each rated at up to 150 watts. This project uses PlatformIO to load the appropriate libraries. Note that in Figure 9, a feedforward controller based on (2. There are two software parts to this project currently, each requiring their own ESP32 device to run. The system will be modeled and a controller will be designed to meet performance The current sampling and pulse width modulation (PWM) duty cycle update methods currently in use in permanent magnet synchronous machine (PMSM) servo control systems introduce significant delays, thereby impacting the motor’s current loop bandwidth and dynamic characteristics to some extent. Jun 6, 2021 · In this video, I will show you how you can control a Stepper Motor remotely, using WiFi, from your phone, and with that feature, you will be able to tune a M Box_3D_Printer folder is about a box project to use with this project of antenna tuner on Alexloop Magnetic loop antenna or similar. The two ends of the loop wire are connected to the twisted extension cable, which in turn connects to the vehicle detector. II. They can be installed close to the ground whilst still having an efficiency close to that of an open dipole antenna. zt vo zt au tn wh wi mw sj fk