The parasitic reactances near the feed-point also vary between installations. Jim, do you mind if I add your email and my answer as a comment to the article? So the differences I see in the data sheets hysteresis curves are not the correct explanation. From that we can find Mismatch Loss. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? 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. . Hence, there is no optimum single-fit solution. Refurbishing aluminium antenna parts affected by weather / corrosion. So, I embarked on testing it for myself. Contact Commercial Coils Consider the RC time for a source with 2500 impedance into a 1pF capacitor. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. There is much more that can be written about this antenna and its matching, but that was not my aim. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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. It is worth experimenting with its length also. How badly can high Local Ambient QRM affect HF Radio? 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. Below is the schematic of the final build. Most of the time 5 to 20W will be adequate for activation anyway. I use shock cord to connect the insulator at the end of the wire to my fence. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. 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. This is perhaps one of the most hotly debated rookie topics in. One end is about 5 meters high on an extended fishing pole. Is FT8 popularity growing at the cost of SSB Phone and CW? 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. application of Kirchhoff's current Law on a typical EFHW antenna configuration. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? And not all hf antenna installation are same, with most requiring bit of tinkering. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 2006. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. It requires a set distance to hang both ends of the antenna, and that is not always given. 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. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. A 100pF silvered mica was connected in shunt with the transformer . Why had I not noticed this before? The transformer fits sideways in the box with a few millimeters to spare. Lowest frequency = 7.000 MHz. The difference here is that the target bands are low frequency. Start by wrapping the wire around the toroid. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Many people use an inductor placed at the near end to make things level out on the higher bands. 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. Transmitting on 15 meters was impossible because of RF into the radio. 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 wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). 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. Some hams swear by them, yet some completely demean it. How to tune a multi-band EFHW antenna using a loading coil 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. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Apply for the Job in Software Engineer - EDI at St. Louis, MO. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! 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 that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. One point of my small-core, compact winding design was to be able to cool the core. I dont have an amplifier, so only need to be able to handle 100W. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. My End-Fed Half-Wave (EFHW) AmateurRadio.com Thanks for your comments. Subscribe to our newsletter and receive regular updates on new posts and articles. 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. Krem, rja le, mi a krdse. I mounted the transformer on a tree for testing. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. It does not need any special components; in fact, most of us may have them in our shack drawers already. 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. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. What kind of balun is this? CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? 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. Let me review the salient observations from the previous work. The Truth, ,and Nothing But The Truth (as I've experienced it) Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. This gave me an effective coil diameter of 40.5mm. For a quarter wave that is about 8 nS. As is often the case, packaging was determined by what boxes I had laying around. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. Independent Medical Evaluation - IME | Cynthia Hennessey In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. It will present its parameters, so anybody with basic home-brew skills will be able to build it. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. The bridge than will measure zero voltage across the bridge, and the LED will turn off. Firstly, bandwidth on 80m is restricted to about 80 kHz at . I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Your posting put it all together for meTHANK YOU!!!! 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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). 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. How far could it possibly reach? Regards VE9HAM. Z8Vq9_@x C\Agv#. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. I particularly want to know how counterpoise affects the common mode currents on the coax. I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. 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 technical storage or access that is used exclusively for statistical purposes. EFHW Antenna Frequency Compensation Lead - YouTube The biggest uncertainty in these measurements was the actual power level used. Above is a sweep of the uncompensated prototype with a 3220+50 load. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. Im very happy with the result. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. I settled on a compact secondary using #28 wire. We use cookies to optimize our website and our service. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube Be sure to take a look for additional analysis and conclusions. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. I was curious why this capacitor was added to the transformer. 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. 3) Total losses are approximately independent of core volume. 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. Why does a wire carrying RF current radiates to produce EM waves which travel through, Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 1. Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). If you really want to get the heat out, add some fins to the aluminum box. It performed well on both the 2m and 70cm bands. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. For . We need to measure the inductances of the toroid with the tapped coil. Engineering the EFHW 49:1 Transformer and Antenna I used four parallel #28 wires (not twisted) for the primary. Look at the compensation coil slide. 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. 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 is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. There is lot of controversy around the EFHW antennas. This antenna is working for 80,40,20,10 and 6m bands. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). blue: 250pF, to much compensation. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Wrap the first wire around the toroid 27 times (I used a black wire for this). Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Klubunknl folyamatos a tagfelvtel. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. 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. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. I found it very useful to label the tuner with switch and capacitance positions. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Zin=46.52+j6.72. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC In this case, it looks important. Check your inbox or spam folder to confirm your subscription. . For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. 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. Also find news related to Efhw Compensation Coil Experiment which is trending today. It depends on the selection of the inductance and the capacitor values. It performed well on both the 2m and 70cm bands. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Is it any good? Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. It is not necessary to calculate the above; the results are sown in the following table. 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. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. The SWR results are as follows: And now I am planning to build one for 160/80m. Then I covered the coil in kapton tape to hold it together. I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. You can start with the links below. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Which begs the question what happens when you attach the antenna? MyAntennas.com Group | When I'm measuring the half way point on my EFHW 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 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. 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. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Compensation. % I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. 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 high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Graphed with a log scale, it makes a nice straight line. The End-Fed Half Wave Antenna a bit Differently We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. Change), You are commenting using your Facebook account. We do not know what the actual impedance will be at the end of the antenna radiator. Even at 15W the voltage at the ends may reach 100-200V. To further improve the flux linkage, I wound the primary on top of the secondary. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. 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.) clear. Efhw Compensation Coil Experiment - Local Search Denver Post I tossed the line as far up as I could in a tree. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer A ktelez mezket * karakterrel jelltk. 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. Could it be something to do with the new vertical aerial I had recently installed? 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. The computation method is also touched on. Generally a loading coil has far more inductance and shortens the length of the antenna significantly.