efhw compensation coil efhw compensation coil

Jos van den Helm's (PA1ZP) article published in Radcom: Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. However, a key restriction is its 25W power rating, due to the small matching transformer. I am building an EFHW antenna for my new. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Elnzst krnk, de elsikkadt az zenete. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. I checked the wall brackets and mast, but all the fixings were nice and tight. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. Is it any good? Even at 15W the voltage at the ends may reach 100-200V. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Transmitting on 15 meters was impossible because of RF into the radio. I decided to play with this to see what I could accomplish. On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. The real power limit will be core heating. Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. From that we can find Mismatch Loss. Current Balun 1. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. First, note that the transformer has low transmission loss up to nearly 50MHz. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. So, how to construct an end-fed half wave antenna? This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, Once I had upgraded the matching transformer for my EF-10/20/40 MKII "EndFedz" (see Part 1) my thoughts turned to the loading coil. One end is about 5 meters high on an extended fishing pole. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. Change), You are commenting using your Twitter account. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. This is perhaps one of the most hotly debated rookie topics in. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . I ran WSPR at 10mW for about 2 hours and got the results below. It is clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. The SWR was measured for each of the three antennas across the CW portion of the bands. A radio station is as good or as bad as the antenna it has. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. . I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Cmzett: Weince joseph How can we help? Thank you for an interesting and informative read. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. 100W on a Wire Antenna - Is it good enough for DX? Then I covered the coil in kapton tape to hold it together. One way or another there is always a counterpoise involved if the antenna is tuned correctly. Can I get away with no capacitor in my design? (LogOut/ Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. I added some Christmas colored zip ties to hold everything in place. It is all about getting the heat out. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Firstly, bandwidth on 80m is restricted to about 80 kHz at . It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. One possible explanation is that the core losses drop with temperature. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. IIRC they call it a "compensator". The technical storage or access that is used exclusively for statistical purposes. There is much more that can be written about this antenna and its matching, but that was not my aim. It may be one or even five kilo-ohms. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. The goal of the temperature characterization is to determine how much temperature difference (core to ambient) there will be for a given level of power dissipation. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. More designs can be found by Googling "80m loaded dipole.". Could it be something to do with the new vertical aerial I had recently installed? This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. But systems that work better increase the prospects of contacts. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). Consider the RC time for a source with 2500 impedance into a 1pF capacitor. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). A method for estimating the impedance of a ferrite cored toroidal inductor at RF. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. VK1OD.net (offline). Change). I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. . Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. It performed well on both the 2m and 70cm bands. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. No wire counterpoise is used to reproduce the SOTA setup. The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. The original coil is designed for low power portable applications. Graphed with a log scale, it makes a nice straight line. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. Your posting put it all together for meTHANK YOU!!!! http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. In his article, I will try to bust some of the myths associated with Inverted. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. Lowest frequency = 7.000 MHz. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. By using traps, the antenna works on all three bands with no operator interaction. The highest voltages as well as radiation are also at the end of the antenna wire. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. Compensation. Zin=46.52+j6.72. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. coil inductance calculator at 66pacific.com. 2. The equation in the article is corrected now. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. The transformer fits sideways in the box with a few millimeters to spare. Does your station desperately need a good RF ground to behave properly? = 258 * 10^-12. It will present its parameters, so anybody with basic home-brew skills will be able to build it. What kind of balun is this? Increasing the drive impedance tends to move the resonances to slightly higher frequencies. The aluminum box is the logical heatsink, so I cut a few scraps of aluminum to make a thermal connection to the bottom of the box and to the lid, adjusting with aluminum shims so that when the box lid is screw down, the entire thermal assembly, with the cores in the middle, is under a little compression. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Highest frequency = 14.350 MHz. blue: 250pF, to much compensation. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. 73! I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. How does this SWR meter works? Looking at several builds and discussions, such as commercial antennas (e.g. Interpretation of S-Meter Noise Floor in HF Radio Receivers. . Copyright 2014-2023. See the second completed tuner depicted below. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. The worse SWR was 1:1.7 at the top end of 20 meters. If you stare at the above frequency sweeps you will discover a few things. The latest news about Efhw Compensation Coil Experiment. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. And not all hf antenna installation are same, with most requiring bit of tinkering. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. My favorite SOTA antenna is the End-Fed Half Wave Antenna. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. I will go back and have the article corrected. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. We need to measure the inductances of the toroid with the tapped coil. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. Let me review the salient observations from the previous work. It not a loading coil. Nagyon j ez a cikk. 1. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. I am currently working on measurements of an EFHW antenna. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. Will there be the same performance for single band EFHWs? A week or two later I started to notice an occasional knocking sound inside the house. We also need to know what are the frequencies or bands for which we plant to use this antenna. 2 0 obj It is hard to wait an infinitely long time for the box to equilibrate to a given power level. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Impressive article and so well done that I may give it a try. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Above, 3t on the primary delivers Gcore<0.002S. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. I needed to add an additional coil (approx 12.5 uH) about . SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency).