The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. blue: 250pF, to much compensation. Regards VE9HAM. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Wrap the first wire around the toroid 27 times (I used a black wire for this). Even at 15W the voltage at the ends may reach 100-200V. Well, in ham radio, everything works. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. The results are presented below. 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. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . This is perhaps one of the most hotly debated rookie topics in. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. Trapped five band EFHW SOTA antenna. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. I look at the end-fed as just an extreme example of an off-center-fed antenna. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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'. . = .000001 / 3868.88 One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Below is the schematic of the final build. 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. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. <> Krem, rja le, mi a krdse. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. 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. I am currently working on measurements of an EFHW antenna. I assume you know the GNARC source for EFHW antennas. Can a diode be used to rectify signals smaller than its threshold voltage? By using traps, the antenna works on all three bands with no operator interaction. It requires a set distance to hang both ends of the antenna, and that is not always given. We do not know what the actual impedance will be at the end of the antenna radiator. Basu Bhattacharya (VU2NSB). From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. One way or another there is always a counterpoise involved if the antenna is tuned correctly. Ismerje meg a hozzszls adatainak feldolgozst . 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. 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. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. They will be adjusted for resonance at or close to the CW portion of the bands. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. See the table above. I particularly want to know how counterpoise affects the common mode currents on the coax. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. = 1/30.e6 = 33 nS. High self-resonant frequency. I needed to add an additional coil (approx 12.5 uH) about . Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. This will yield the minimal capacitance of the variable capacitor. 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 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The overlaid VSWR plots are shown below. Some hams swear by them, yet some completely demean it. The final turns ratio turned out to be 3:29. It does not need any special components; in fact, most of us may have them in our shack drawers already. 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. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. It may be one or even five kilo-ohms. Make sure the first wire is wrapped evenly around the whole toroid. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. 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. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. 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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. Why does antenna radiation occur? 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. 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. Isn't it? Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. Thank you for an interesting and informative read. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Let's find out! I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. 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. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. 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. 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. The biggest uncertainty in these measurements was the actual power level used. Also find news related to Efhw Compensation Coil Experiment which is trending today. Which begs the question what happens when you attach the antenna? Could it be something to do with the new vertical aerial I had recently installed? 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. 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 swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Is FT8 popularity growing at the cost of SSB Phone and CW? . Impressive article and so well done that I may give it a try. I checked the wall brackets and mast, but all the fixings were nice and tight. Elnzst krnk, de elsikkadt az zenete. Compensation. In this case, it looks important. It depends on the selection of the inductance and the capacitor values. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. More designs can be found by Googling "80m loaded dipole.". 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. And of course, a counterpoise with various lengths. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. 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. 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. 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. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. How to get started on ISS Cross band Repeater? I dont have an amplifier, so only need to be able to handle 100W. The transformer fits sideways in the box with a few millimeters to spare. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. It should be no surprise that 80pF is close to optimal. Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. Above is a sweep of the roughly compensated transformer. Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. Zin=46.52+j6.72. Klubunknl folyamatos a tagfelvtel. If you stare at the above frequency sweeps you will discover a few things. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Thank you Gary. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. You can see the coil in the picture below (red arrow). Thank you for your comment and feedback on the article about the EFHW antenna. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. P.S. 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. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. What are the advantages and disadvantages of the end-fed half wave antenna? In comparison to the EFHW antenna, a simple dipole offers a far better prospect. 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. 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. 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. 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'. 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. The worse SWR was 1:1.7 at the top end of 20 meters. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Wow, Gary! Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. Change), You are commenting using your Facebook account. Let us touch on some necessary theory to begin with. 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. Below about 7 MHz, transmission losses increase as the core temperature increases. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. 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. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. coil inductance calculator at 66pacific.com. However, it has its idiosyncrasies. The original coil is designed for low power portable applications. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. I then used a piece of heat shrink on the outside to hold everything in place. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 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. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. Nagyon j ez a cikk. Apply for the Job in Software Engineer - EDI at St. Louis, MO. Start by wrapping the wire around the toroid. 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. 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. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. So the differences I see in the data sheets hysteresis curves are not the correct explanation. 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. VK1OD.net (offline). It is quite possible that designing more than three or four bands into a tuner will lead to a failure. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. The bridge than will measure zero voltage across the bridge, and the LED will turn off. 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. Will there be the same performance for single band EFHWs? Im very pleased with that indeed. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Highest frequency = 14.350 MHz. I can give a link if you need. I checked the wall brackets and mast, but all the fixings were nice and tight. It is worth experimenting with its length also. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver.
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