= 258 * 10^-12. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. 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. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. The final turns ratio turned out to be 3:29. Above is a sweep of the uncompensated prototype with a 3220+50 load. It not a loading coil. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings. 1. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Highest frequency = 14.350 MHz. 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. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. 3) Total losses are approximately independent of core volume. The cooling curve I measured is shown below. The Counterpoise is a short, typically one twentieth (0.05 *. ) The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. The band compensating inductor placed on the wire is another story. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. The EFHW transformer box from outside. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Change), You are commenting using your Facebook account. 100W on a Wire Antenna - Is it good enough for DX? Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. 5) It is very hard to avoid stray capacitance on the output. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? The technical storage or access that is used exclusively for anonymous statistical purposes. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Krem, rja le, mi a krdse. My design objectives were: 1. In theory, the examination is supposed to be used to help clarify your medical condition and . This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. 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. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. We need to measure the inductances of the toroid with the tapped coil. In this case, it looks important. Make sure the first wire is wrapped evenly around the whole toroid. The results are presented below. application of Kirchhoff's current Law on a typical EFHW antenna configuration. The SWR was measured for each of the three antennas across the CW portion of the bands. Some hams swear by them, yet some completely demean it. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! The SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters. It is worth experimenting with its length also. 100W on a Wire antenna! But before we do, let us look at the insertion and transmission loss that the VNA is reporting. Zin=46.52+j6.72. Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. Hence, there is no optimum single-fit solution. How to get started on ISS Cross band Repeater? If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. You can see the coil in the picture below (red arrow). 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. 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. No capacitor was installed. I use shock cord to connect the insulator at the end of the wire to my fence. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. 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. This article will not address that antenna type. 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. Very interesting design. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. 73! How big and where to place it is likely best determined empirically. The basic question before us is how does an antenna work? If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. This will also be handling 100W. This gave me an effective coil diameter of 40.5mm. Well, in ham radio, everything works. Be cautious, such voltages may cause a quite painful skin scorch. 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. Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. ROB@COMCOIL.COM Research salary, company info, career paths, and top skills for Software Engineer - EDI 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. Let's find out! The antennas are set up as a sloper as in my SOTA outings. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. This is typically a weak spot. They will be adjusted for resonance at or close to the CW portion of the bands. 73 With no counterpoise wire it will be the coaxs shield providing it. You can start with the links below. 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. Wrap the first wire around the toroid 27 times (I used a black wire for this). 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. Will there be the same performance for single band EFHWs? It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. I wish you lots of productive experimentations and successful portable operations. The SWR results are as follows: I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. Some say you do not need a counterpoise, but that is false. Z8Vq9_@x C\Agv#. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. Workers' Comp. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. But I would caution its usage for higher power than 10-15W. Looking at several builds and discussions, such as commercial antennas (e.g. No wire counterpoise is used to reproduce the SOTA setup. What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. Next, I started winding the transformer. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. The next important parameter is the parallel resonant circuits resonant frequency. There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. . A week or two later I started to notice an occasional knocking sound inside the house. 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. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. . 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. VSWR<1.8 over all of HF. Many people use an inductor placed at the near end to make things level out on the higher bands. It uses a coil as a compensation unit, and no counterpoise. To explore parameter space a little, I modeled a couple of lengths for the counterpoise and see how the wire is resonant across the band when fed with various impedances at the driven point. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Thanks for your comments. I am planning to use this latest one at the Field Day next year. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). I added some Christmas colored zip ties to hold everything in place. : I see you were able to post your comment now, so I just copied my email answer here for others to see. If you really want to get the heat out, add some fins to the aluminum box. 2015. It performed well on both the 2m and 70cm bands. This can then, fed with coaxial cable, in many cases be . Current Balun 1. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. Can I get away with no capacitor in my design? I decided to play with this to see what I could accomplish. To further improve the flux linkage, I wound the primary on top of the secondary. Most informative and appreciated. Is it any good? I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. I look at the end-fed as just an extreme example of an off-center-fed antenna. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. In the case of the EFHW 49:1 transformer, the major shortcomings of the most popular current designs are excessive leakage inductance and poor heat transfer from the ferrite material to the environment. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. The 2 coils are 35uh and 90uh. However, the insertion loss of the packaged transformer would be intolerable on the 10 meter band if it appeared the same way with an antenna wire connected. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. Change), You are commenting using your Twitter account. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The technical storage or access that is used exclusively for statistical purposes. 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. (LogOut/ An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. The transformer fits sideways in the box with a few millimeters to spare. Your article was well written and very informative, thanks. Your posting put it all together for meTHANK YOU!!!! I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. Understanding Antennas The Good, the Bad, and the Ugly. I particularly want to know how counterpoise affects the common mode currents on the coax. This is indeed a classic antenna that is not only, Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. That will be the missing resistor in the resistor bridge of the below circuit. A 100pF silvered mica was connected in shunt with the transformer primary. The coil is just 12 turns of wire wrapped around a 0.7 inch diameter tube, located about 6 feet past the antenna's feedpoint. The antenna is effective and the materials and construction are of a very high quality. It is not necessary to calculate the above; the results are sown in the following table. More designs can be found by Googling "80m loaded dipole.". The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. . Ive spent some time on digital modes over the last week and and my signal reports seem very similar to the pre-80m-extension period, which is good, and I am getting out well past 1000 miles on 20, 40m and 80m digital. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. Can you give me an idea for your 100 W version, you built for 80/60/40 m. 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. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. Lowest measured inductivity = 2.0 H. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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. 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. Subscribe to our newsletter and receive regular updates on new posts and articles. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. This is perhaps one of the most hotly debated rookie topics in. Above 7MHz, there is very little temperature dependence at all. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. I am building an EFHW antenna for my new. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. Throw one end of the antenna wire, extended with a rope, as high as you can on a three, and walk away with the other end and attach it to the tuner. Start by wrapping the wire around the toroid. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. |k"^N>F.AnJkJsq'PV}o0I. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. blue: 250pF, to much compensation. Not the ideal antenna, but convenient! I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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 difference here is that the target bands are low frequency. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. I decided to push for best efficiency with a 5-turn primary. There is much more that can be written about this antenna and its matching, but that was not my aim. 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. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. But Ill find the error of my ways.and there are various on-line calculators to help me ensure I get the decimals and (H, mH, uH, pH, etc.) This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. However, a key restriction is its 25W power rating, due to the small matching transformer. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. Looking at several builds and discussions, such as commercial antennas (e.g. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. Impressive article and so well done that I may give it a try. One point of my small-core, compact winding design was to be able to cool the core. I settled on a compact secondary using #28 wire. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. At this point, I'm leaning towards the EFHW, but any of these antennas seem . This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. I found that sometimes the multimeter that was measuring the temperature would give unreliable information when RF was present, so the off periods provided regular intervals for measuring the temperature. (Tvir s tvbeszl gpek s kszlkek) Ksznm. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. I tossed the line as far up as I could in a tree.