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. Your posting put it all together for meTHANK YOU!!!! A 100pF silvered mica was connected in shunt with the transformer . We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. And not all hf antenna installation are same, with most requiring bit of tinkering. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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. Current Balun 1. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. Not the ideal antenna, but convenient! I used the 14g enameled wire and wound it on the FT240-43. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. = 1/30.e6 = 33 nS. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. It should be no surprise that 80pF is close to optimal. Note: If we change the primary number of turns, the impedance ratios will considerable change also. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. In theory, the examination is supposed to be used to help clarify your medical condition and . It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. 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. 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 following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). 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I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). This suggests an inductive reactance. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. 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. Best regards and thanks again for your comment. Hi Ajai, When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Even at 15W the voltage at the ends may reach 100-200V. = 258 * 10^-12. The equation in the article is corrected now. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. No wire counterpoise is used to reproduce the SOTA setup. There are two aspects, however that we need to consider: Lets begin with the transformer. I tossed the line as far up as I could in a tree. Instead, this shifts everything down and makes it very easy to tune 10m. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. However, a key restriction is its 25W power rating, due to the small matching transformer. There are many good descriptions on the net about this type of antenna. 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" 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. 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. I first mounted the SO239 connector to the box. 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. 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. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. 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. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. A week or two later I started to notice an occasional knocking sound inside the house. 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. (LogOut/ 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. 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. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. With such a switch, it is impossible to forget to switch back to operational mode. 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. 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 matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. Jim, do you mind if I add your email and my answer as a comment to the article? 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). 100W on a Wire antenna! Wrap the first wire around the toroid 27 times (I used a black wire for this). I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. 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). In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. = .000001 / 3868.88 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. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. It is worth experimenting with its length also. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Your article was well written and very informative, thanks. 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. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Trapped five band EFHW SOTA antenna. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 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. 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. Make sure the first wire is wrapped evenly around the whole toroid. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. Two layers of 1mil Kapton tape are placed over the winding. In this case, it looks important. The 2 coils are 35uh and 90uh. There is much more that can be written about this antenna and its matching, but that was not my aim. The SWR figures were as follows: FT240-43 132ft/100pF capacitor 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. blue: 250pF, to much compensation. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. I settled on a compact secondary using #28 wire. stream The results are shown below. Lowest frequency = 7.000 MHz. 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. I am building an EFHW antenna for my new. My design objectives were: 1. 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. 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. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. It is important to consider the voltages on this tank circuit. 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. 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. 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. Most informative and appreciated. Very interesting design. 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? Which begs the question what happens when you attach the antenna? Thirty turns #28 are wound on the two FT114-43 cores. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Of course, you will need to find your tuning positions and apply your own position scale. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Frank VK1VK. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. The resistance (real) component of the impedance is right where we want it near 50 ohms. 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 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. Workers' Comp. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. There is lot of controversy around the EFHW antennas. It requires a set distance to hang both ends of the antenna, and that is not always given. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. clear. 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. 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. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. One point of my small-core, compact winding design was to be able to cool the core. Why had I not noticed this before? The antenna is effective and the materials and construction are of a very high quality. 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. Does your station desperately need a good RF ground to behave properly? I was curious why this capacitor was added to the transformer. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. And now I am planning to build one for 160/80m. Be aware counterpoise or ground radials are required for all hf antennas for better performance. 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. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. It does not need any special components; in fact, most of us may have them in our shack drawers already. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. The antennas are set up as a sloper as in my SOTA outings. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. So I built myself an improved replacement matching transformer. Consequently, this is how the capacitance values are determined. Some hams swear by them, yet some completely demean it. We use cookies to optimize our website and our service. My favorite SOTA antenna is the End-Fed Half Wave Antenna. . The computation method is also touched on. See the table above. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. 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. The overall lenght is only 15m. It uses a coil as a compensation unit, and no counterpoise. . Z8Vq9_@x C\Agv#. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. 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). 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. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. I wish I had a simple answer, but really this is where some experimentation can pay off. The radiation pattern of this antenna on most bands produces multiple lobes. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Im very happy with the result. ROB@COMCOIL.COM 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. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. 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. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. |k"^N>F.AnJkJsq'PV}o0I. Refurbishing aluminium antenna parts affected by weather / corrosion. Also find news related to Efhw Compensation Coil Experiment which is trending today. 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. You can start with the links below. 2015. 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. With no counterpoise wire it will be the coaxs shield providing it. This will yield the minimal capacitance of the variable capacitor. It is recommended to use at least 2W non-inductive resistors for this purpose. A 100pF silvered mica was connected in shunt with the transformer primary. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. This gave me an effective coil diameter of 40.5mm. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. But systems that work better increase the prospects of contacts. The SWR for the 20 meter EFHW antenna was < 1.2:1 I am currently working on measurements of an EFHW antenna. How to get started on ISS Cross band Repeater? 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. 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. The worse SWR was 1:1.7 at the top end of 20 meters. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Elnzst krnk, de elsikkadt az zenete. The tests here were using a dummy load on the transformer, and that did allow confirmation of the design and expected loss at 3.6MHz. Can you give me an idea for your 100 W version, you built for 80/60/40 m. I wish you lots of productive experimentations and successful portable operations. The technical storage or access that is used exclusively for anonymous statistical purposes. A radio station is as good or as bad as the antenna it has. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Looking at several builds and discussions, such as commercial antennas (e.g. How big and where to place it is likely best determined empirically. The previous table already contains these measurements. First, note that the transformer has low transmission loss up to nearly 50MHz. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH 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. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. So, how to construct an end-fed half wave antenna? Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Looking at several builds and discussions, such as commercial antennas (e.g. 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. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Lets call this element the LoadAttenuator. I will publish my findings, but I cannot not promise to complete it until early fall. The model results show the need for a not entirely insignificant counterpoise. In an urban area we are much more restricted, especially if we need to be stealth about it. 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. 73 (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . 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. 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. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. 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. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. 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. You cant really see the antenna wire, but the red line shows the antenna path. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Hello, a wonderful approach for the problems.. Compensation. And of course, a counterpoise with various lengths. Let me review the salient observations from the previous work. The results are presented below. More designs can be found by Googling "80m loaded dipole.". It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. 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.
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efhw compensation coil