The final turns ratio turned out to be 3:29. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. (LogOut/ For . So, I embarked on testing it for myself. How badly can high Local Ambient QRM affect HF Radio? Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. 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. How to get started on ISS Cross band Repeater? By using traps, the antenna works on all three bands with no operator interaction. 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. Is FT8 popularity growing at the cost of SSB Phone and CW? From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. The highest voltages as well as radiation are also at the end of the antenna wire. 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. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. It depends on the selection of the inductance and the capacitor values. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. 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'. I am building an EFHW antenna for my new. I added some Christmas colored zip ties to hold everything in place. It is worth experimenting with its length also. It is recommended to use at least 2W non-inductive resistors for this purpose. 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Can a diode be used to rectify signals smaller than its threshold voltage? The impedance per unit length of a lumped transmission line is where L and C are values per unit length. 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. Zin=46.52+j6.72. In his article, I will try to bust some of the myths associated with Inverted. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. Wrap the first wire around the toroid 27 times (I used a black wire for this). If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. It is better to build one for 160 and 80m, perhaps add 17m to the design described in this article, and for higher bands it is easier to use a linked dipole. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. This is typically a weak spot. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Do I count the six loops around the pvc in the measurement? I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. Be sure to take a look for additional analysis and conclusions. You can start with the links below. The biggest uncertainty in these measurements was the actual power level used. As is often the case, packaging was determined by what boxes I had laying around. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. It not a loading coil. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Instead, this shifts everything down and makes it very easy to tune 10m. I use shock cord to connect the insulator at the end of the wire to my fence. 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. See the second completed tuner depicted below. 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. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. It requires a set distance to hang both ends of the antenna, and that is not always given. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. 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. With no counterpoise wire it will be the coaxs shield providing it. Could it be something to do with the new vertical aerial I had recently installed? Understanding Antennas The Good, the Bad, and the Ugly. If we wish to limit the ferrite temperature to 130 C, then assuming ambient temperature of 30 C, we can tolerate a 100 C temperature rise. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). Hence, we need to move along and start to include the antenna with our testing. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. Make sure the first wire is wrapped evenly around the whole toroid. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. For the last step, I put together a RF choke to use between the radio and the feedline. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. 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. After some internet research, I settled on making the former from a paint roller. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. It will present its parameters, so anybody with basic home-brew skills will be able to build it. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. 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 use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. 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. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR. The model results show the need for a not entirely insignificant counterpoise. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. So, how to construct an end-fed half wave antenna? On the transformer, I added a few wingnuts to tighten down the antenna wire. 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. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. What kind of balun is this? Z8Vq9_@x C\Agv#. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Above is a sweep of the uncompensated prototype with a 3220+50 load. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. This can then, fed with coaxial cable, in many cases be . Why had I not noticed this before? Why had I not noticed this before? On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. P.S. 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. 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 blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Let me review the salient observations from the previous work. I wish you lots of productive experimentations and successful portable operations. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). However, in reality, the term Omnidirectional needs to be taken in the context of the communication. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. This antenna is working for 80,40,20,10 and 6m bands. The 2 coils are 35uh and 90uh. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. = .00 00 00 00 0 258 The antenna is effective and the materials and construction are of a very high quality. 1. 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. Krem, rja le, mi a krdse. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. The worse SWR was 1:1.7 at the top end of 20 meters. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. 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. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. To be safe, better not get much above 120 C. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. coil inductance calculator at 66pacific.com. 2006. This is not an optimal value, benefit may be obtained by exploring small changes to that value. 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. 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.) My favorite SOTA antenna is the End-Fed Half Wave Antenna. 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. It is important that resonance may be achieved at each tap of the inductance. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. We need to measure the inductances of the toroid with the tapped coil. Ismerje meg a hozzszls adatainak feldolgozst . I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. If you stare at the above frequency sweeps you will discover a few things. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. One possible explanation is that the core losses drop with temperature. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. I can give a link if you need. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. The toroid with its many taps may be soldered directly on a multi-position switch. There are many good descriptions on the net about this type of antenna. 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . Hello, a wonderful approach for the problems.. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. The original coil is designed for low power portable applications. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. Most informative and appreciated. 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. 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. All Rights Reserved. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. No wire counterpoise is used to reproduce the SOTA setup. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. For a quarter wave that is about 8 nS. Consequently, this is how the capacitance values are determined. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. I used the 14g enameled wire and wound it on the FT240-43. I then added two 220pf capacitors in series between the center conductor and ground. 2 0 obj One point of my small-core, compact winding design was to be able to cool the core. 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. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 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 typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. It is best to make the impedance matching adjustable, using switched transformation ratio. 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. 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. Proudly created withWix.com.
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