The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. 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 may be one or even five kilo-ohms. One end is about 5 meters high on an extended fishing pole. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. 1. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. The next important parameter is the parallel resonant circuits resonant frequency. Of course, if both ends are raised higher, it will produce a more efficiently radiating antenna, but the portable and temporary installation is always compromised by conditions given by a location and its restrictions. 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. There are two aspects, however that we need to consider: Lets begin with the transformer. These dimensions were derived from modelling the antenna in EZNEC. Lowest measured inductivity = 2.0 H. We do not know what the actual impedance will be at the end of the antenna radiator. My design objectives were: 1. It is all about getting the heat out. Is FT8 popularity growing at the cost of SSB Phone and CW? If you stare at the above frequency sweeps you will discover a few things. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. With such a switch, it is impossible to forget to switch back to operational mode. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. I then added two 220pf capacitors in series between the center conductor and ground. 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. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. 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. Why had I not noticed this before? 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. Lets do a quick calculation to see how much an issue is this output capacitance. 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. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Just the bare 80m wire is shown in red. The bridge than will measure zero voltage across the bridge, and the LED will turn off. The final turns ratio turned out to be 3:29. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. The SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. 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. The antennas are set up as a sloper as in my SOTA outings. Graphed with a log scale, it makes a nice straight line. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Can you give me an idea for your 100 W version, you built for 80/60/40 m. 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. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. I am currently working on measurements of an EFHW antenna. 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? 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. Thank you Gary. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. This reveals we only need to compensate for the reactive component. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. Does your station desperately need a good RF ground to behave properly? I will publish my findings, but I cannot not promise to complete it until early fall. Impressive article and so well done that I may give it a try. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. 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. 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. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. I tossed the line as far up as I could in a tree. 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. 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. In this case, it looks important. 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. 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. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. And of course, a counterpoise with various lengths. 2015. 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. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. 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. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. What kind of balun is this? The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. (Tvir s tvbeszl gpek s kszlkek) Ksznm. 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. So far so good. 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. There is lot of controversy around the EFHW antennas. High Q, hence low loss. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Instead, this shifts everything down and makes it very easy to tune 10m. 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. 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. = .000001 / 3868.88 Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). This will also be handling 100W. Could it be something to do with the new vertical aerial I had recently installed? It is not necessary to calculate the above; the results are sown in the following table. 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. See the second completed tuner depicted below. Highest frequency = 14.350 MHz. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. 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. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. I can give a link if you need. 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. Transmitting on 15 meters was impossible because of RF into the radio. One way or another there is always a counterpoise involved if the antenna is tuned correctly. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. 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. Csatlakozz csapatunkhoz! Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. I found it very useful to label the tuner with switch and capacitance positions. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. Z8Vq9_@x C\Agv#. 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. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. And not all hf antenna installation are same, with most requiring bit of tinkering. I then used a piece of heat shrink on the outside to hold everything in place. Change), You are commenting using your Twitter account. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Klubunknl folyamatos a tagfelvtel. Some website features may not function optimally without cookies. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 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??). Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. 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. 100W on a Wire Antenna How far would it reach? The basic question before us is how does an antenna work? Krem, rja le, mi a krdse. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. 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! But I would caution its usage for higher power than 10-15W. Next, I started winding the transformer. As I reexamined my formula, you pointed it out correctly, there is an error in it. 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. 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). The toroid with its many taps may be soldered directly on a multi-position switch. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 73! How does this SWR meter works? It performed well on both the 2m and 70cm bands. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . 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. Basu Bhattacharya (VU2NSB). 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. The wire as I strung it up seemed to resist having a good SWR for the 20m band. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. Above, 3t on the primary delivers Gcore<0.002S. My favorite SOTA antenna is the End-Fed Half Wave Antenna. 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. The final turns ratio turned out to be 3:29. Very interesting design. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. 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. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. I was curious why this capacitor was added to the transformer. Change). The highest voltages as well as radiation are also at the end of the antenna wire. Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. Is it any good? To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. 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. The equation in the article is corrected now. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. 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. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. Finally the tank circuits specification is complete, which is sown below. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Best regards and thanks again for your comment. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. So the differences I see in the data sheets hysteresis curves are not the correct explanation. 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The impedance matching circuit is essentially a simple parallel resonant LC circuit. I checked the wall brackets and mast, but all the fixings were nice and tight. A 100pF silvered mica was connected in shunt with the transformer . = .00 00 00 00 0 258 I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. Isn't it? 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. This can then, fed with coaxial cable, in many cases be . 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. = 1/30.e6 = 33 nS. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. of the wavelength. Im very pleased with that indeed. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Thank you for your comment and feedback on the article about the EFHW antenna. The original coil is designed for low power portable applications.

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