of the wavelength. 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. Lowest measured inductivity = 2.0 H. I was curious why this capacitor was added to the transformer. 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 EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. 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). Frank VK1VK. Many people use an inductor placed at the near end to make things level out on the higher bands. Impressive article and so well done that I may give it a try. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. The antenna is up. 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. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. For our transformer at 100W (==> 71 Vrms into 50 ) , the core cross section for the two FT114s is 0.74 cm2 , consider the lowest frequency as 3.5 MHz and our 5-turn primary, then plugging in the numbers we find Bmax = 0.012 T. Lets consider a much more challenging extreme: 1000W and the 160m band. The antenna is effective and the materials and construction are of a very high quality. My favorite SOTA antenna is the End-Fed Half Wave Antenna. . No wire counterpoise is used to reproduce the SOTA setup. Can you give me an idea for your 100 W version, you built for 80/60/40 m. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 5) It is very hard to avoid stray capacitance on the output. I then used a piece of heat shrink on the outside to hold everything in place. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. Thank you Gary. Some website features may not function optimally without cookies. 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. It is best to make the impedance matching adjustable, using switched transformation ratio. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. I am planning to use this latest one at the Field Day next year. Will there be the same performance for single band EFHWs? (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. Looking at several builds and discussions, such as commercial antennas (e.g. Trapped five band EFHW SOTA antenna. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Lets call this element the LoadAttenuator. Isn't it? Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Hello, a wonderful approach for the problems.. The original coil is designed for low power portable applications. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. Thanks! Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. It uses a coil as a compensation unit, and no counterpoise. What are the advantages and disadvantages of the end-fed half wave antenna? But systems that work better increase the prospects of contacts. 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. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. Start by wrapping the wire around the toroid. Above is a sweep of the uncompensated prototype with a 3220+50 load. 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). 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. . 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. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. The coil came out at 89mm in length rather than the theoretical 83mm not surprisingly, but the inductance was bang on at just over 109H. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. There are two aspects, however that we need to consider: Lets begin with the transformer. stream 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. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. : I see you were able to post your comment now, so I just copied my email answer here for others to see. 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. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Elnzst krnk, de elsikkadt az zenete. 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. 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. The overlaid VSWR plots are shown below. It should be no surprise that 80pF is close to optimal. And of course, a counterpoise with various lengths. The smallest number I measured was 1.6 pF, derived from the self-resonance at 41 MHz with the leakage inductance (measured at 198 nH) when the secondary was shorted. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Firstly, bandwidth on 80m is restricted to about 80 kHz at . If you stare at the above frequency sweeps you will discover a few things. And now I am planning to build one for 160/80m. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. 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The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. How does this SWR meter works? Thank you for your comment and feedback on the article about the EFHW antenna. The equation should have a 10^6 and not 10^-6 in the nominator. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Two layers of 1mil Kapton tape are placed over the winding. Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. 73! What are its disadvantages? Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. I would mention first its ease of installation. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Let's find out! I decided to play with this to see what I could accomplish. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. The antennas are set up as a sloper as in my SOTA outings. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. It performed well on both the 2m and 70cm bands. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. I will go back and have the article corrected. Basu Bhattacharya (VU2NSB). Instead, this shifts everything down and makes it very easy to tune 10m. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. Show more. End-Fed antennas are useful in many ways, includes easier mounting of cable at one end (freeing the antenna from unnecessary weight of cable) & antenna maintenance in future. Nagyon j ez a cikk. 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. Check your inbox or spam folder to confirm your subscription. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. So far so good. There are many good descriptions on the net about this type of antenna. Engineering the EFHW 49:1 Transformer and Antenna Does your station desperately need a good RF ground to behave properly? PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC Some hams swear by them, yet some completely demean it. Graphed with a log scale, it makes a nice straight line. For the last step, I put together a RF choke to use between the radio and the feedline. i liked it a lot, you give good ideas, many thanks. ROB@COMCOIL.COM Im very happy with the result. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF Even at 15W the voltage at the ends may reach 100-200V. Do I count the six loops around the pvc in the measurement? Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. In his article, I will try to bust some of the myths associated with Inverted. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! Lowest frequency = 7.000 MHz. 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. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. |k"^N>F.AnJkJsq'PV}o0I. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The equation in the article is corrected now. 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. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. The band compensating inductor placed on the wire is another story. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. The transformer fits sideways in the box with a few millimeters to spare. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. 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. Consequently, this is how the capacitance values are determined. Why had I not noticed this before? 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. This will also be handling 100W. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. 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. Ismerje meg a hozzszls adatainak feldolgozst . Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. You can start with the links below. They will be adjusted for resonance at or close to the CW portion of the bands. 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. We use cookies to optimize our website and our service. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. But I would caution its usage for higher power than 10-15W. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. 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. To be safe, better not get much above 120 C. 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. 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. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. 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. Can I get away with no capacitor in my design? The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. The technical storage or access that is used exclusively for statistical purposes. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. This will yield the maximum capacity of the variable capacitor. 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. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Well, in ham radio, everything works. Taking the time derivative of the above equation you get the power dissipation. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. 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. MyAntennas.com Group | When I'm measuring the half way point on my EFHW 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. You can see the coil in the picture below (red arrow). Below is the schematic of the final build. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. Csatlakozz csapatunkhoz! This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. This gave me an effective coil diameter of 40.5mm. 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio Efhw Compensation Coil Experiment - Local Search Denver Post 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. 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. 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. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. The SWR results are as follows: How-To: Make a Multiband EFHWA for Amateur Ham Radio Could it be something to do with the new vertical aerial I had recently installed? 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. EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. 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. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 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). One possible explanation is that the core losses drop with temperature. % 2015. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. There is lot of controversy around the EFHW antennas. 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. I wish you lots of productive experimentations and successful portable operations. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. My design objectives were: 1. The photos above show a method that works fairly well. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. It is worth experimenting with its length also. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. Although the original loading coil is very well engineered, I thought I could make a more efficient version given that I did not need to make it 'trail friendly'. How badly can high Local Ambient QRM affect HF Radio? From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. I assume you know the GNARC source for EFHW antennas. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. Hence, there is no optimum single-fit solution. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Why had I not noticed this before? On the transformer, I added a few wingnuts to tighten down the antenna wire. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. This antenna is only 15m long using 2 loading coils. 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. Then I covered the coil in kapton tape to hold it together. 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. 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 can give a link if you need. 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. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Finally the tank circuits specification is complete, which is sown below. How far could it possibly reach? This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. 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. Interpretation of S-Meter Noise Floor in HF Radio Receivers. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? 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. The bridge than will measure zero voltage across the bridge, and the LED will turn off. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. The antenna is effective and the materials and construction are of a very high quality.