First, note that the transformer has low transmission loss up to nearly 50MHz. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. The antenna is effective and the materials and construction are of a very high quality. 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. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. A radio station is as good or as bad as the antenna it has. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. The negative effects of local QRM on an, How does antenna radiation occur? I decided to push for best efficiency with a 5-turn primary. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Zin=46.52+j6.72. 2006. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Thanks in advance, good health for you in these times, Show more. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. The 2 coils are 35uh and 90uh. Be aware counterpoise or ground radials are required for all hf antennas for better performance. The highest voltages as well as radiation are also at the end of the antenna wire. Klubunknl folyamatos a tagfelvtel. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? The original coil is designed for low power portable applications. 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. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Look at the compensation coil slide. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. Also find news related to Efhw Compensation Coil Experiment which is trending today. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Apply for the Job in Software Engineer - EDI at St. Louis, MO. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. 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. Just the bare 80m wire is shown in red. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. The overall lenght is only 15m. Your posting put it all together for meTHANK YOU!!!! Make sure the first wire is wrapped evenly around the whole toroid. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. Even at 15W the voltage at the ends may reach 100-200V. The SWR for the 20 meter EFHW antenna was < 1.2:1 The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Not the ideal antenna, but convenient! 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. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Im very pleased with that indeed. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. For the last step, I put together a RF choke to use between the radio and the feedline. High Q, hence low loss. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. Ismerje meg a hozzszls adatainak feldolgozst . Hence, there is no optimum single-fit solution. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. Nagyon j ez a cikk. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). I will publish my findings, but I cannot not promise to complete it until early fall. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. Taking the time derivative of the above equation you get the power dissipation. (Tvir s tvbeszl gpek s kszlkek) Ksznm. This suggests an inductive reactance. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. Isn't it? PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. The latest news about Efhw Compensation Coil Experiment. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. 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. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! This is perhaps one of the most hotly debated rookie topics in. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. A 100pF silvered mica was connected in shunt with the transformer . I then used a piece of heat shrink on the outside to hold everything in place. Change), You are commenting using your Facebook account. It depends on the selection of the inductance and the capacitor values. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. 2 0 obj The final turns ratio turned out to be 3:29. Workers' Comp. Very interesting design. 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. The highest frequency could be14.350MHz. Understanding Antennas The Good, the Bad, and the Ugly. . My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. Let us touch on some necessary theory to begin with. One point of my small-core, compact winding design was to be able to cool the core. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. So the differences I see in the data sheets hysteresis curves are not the correct explanation. . Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. It is important that resonance may be achieved at each tap of the inductance. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. If not a lightning strike, I will write an article about the experience as well. So, how to construct an end-fed half wave antenna? A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. Consequently, this is how the capacitance values are determined. I was curious why this capacitor was added to the transformer. Csatlakozz csapatunkhoz! blue: 250pF, to much compensation. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. How badly can high Local Ambient QRM affect HF Radio? |k"^N>F.AnJkJsq'PV}o0I. A 100pF silvered mica was connected in shunt with the transformer primary. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. The technical storage or access that is used exclusively for anonymous statistical purposes. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. I first mounted the SO239 connector to the box. Note: If we change the primary number of turns, the impedance ratios will considerable change also. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. The impedance matching circuit is essentially a simple parallel resonant LC circuit. Of course, you will need to find your tuning positions and apply your own position scale. All Rights Reserved. Could it be something to do with the new vertical aerial I had recently installed? Hi Ajai, I ran WSPR at 10mW for about 2 hours and got the results below. See the table above. i liked it a lot, you give good ideas, many thanks. My design objectives were: 1. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. What kind of balun is this? Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. 100W on a Wire Antenna How far would it reach? This can then, fed with coaxial cable, in many cases be . This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. Most of the time 5 to 20W will be adequate for activation anyway. This is not an optimal value, benefit may be obtained by exploring small changes to that value. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. Is it any good? Why had I not noticed this before? I would mention first its ease of installation. The resistance (real) component of the impedance is right where we want it near 50 ohms. I came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. Some say you do not need a counterpoise, but that is false. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. 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 is best to make the impedance matching adjustable, using switched transformation ratio. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. nanoVNA-H can firmware be updated if it has a broken USB socket? It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. How does this SWR meter works? document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email. The technical storage or access that is used exclusively for statistical purposes. The model results show the need for a not entirely insignificant counterpoise. As I reexamined my formula, you pointed it out correctly, there is an error in it. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Next, I started winding the transformer. The total lenght is about 15mtr only and using 2 coils and a little stub (s) on the 80m coil or/and the 40m coil. It is very hard to know what will be the best solution for a given antenna installation if you want to hit all of the bands exactly. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. So I built myself an improved replacement matching transformer. The SWR results are as follows: A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. I dont have an amplifier, so only need to be able to handle 100W. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Although it is simple to build and is a multiband antenna, it has several attributes that . I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. No wire counterpoise is used to reproduce the SOTA setup. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. Looking at several builds and discussions, such as commercial antennas (e.g. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Does your station desperately need a good RF ground to behave properly? Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. This antenna is working for 80,40,20,10 and 6m bands. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. It is important to consider the voltages on this tank circuit. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. As you look to use this transformer at higher power levels, I can imagine that the bottleneck might be voltage breakdown or corona in the windings. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. You cant really see the antenna wire, but the red line shows the antenna path. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. It is worth experimenting with its length also. I suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. The previous table already contains these measurements. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. Instead, this shifts everything down and makes it very easy to tune 10m. clear. The toroid with its many taps may be soldered directly on a multi-position switch. This provides proper insulation from the relatively high voltages on the seconder winding. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. Why had I not noticed this before? 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. Let me review the salient observations from the previous work. For a quarter wave that is about 8 nS. In his article, I will try to bust some of the myths associated with Inverted. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver.
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