Even at 15W the voltage at the ends may reach 100-200V. I wish I had a simple answer, but really this is where some experimentation can pay off. The technical storage or access that is used exclusively for statistical purposes. The resistance (real) component of the impedance is right where we want it near 50 ohms. Very interesting design. 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. of the wavelength. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! VSWR<1.8 over all of HF. 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. Does your station desperately need a good RF ground to behave properly? 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. 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. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. 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. Be cautious, such voltages may cause a quite painful skin scorch. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. Now I just need to build or acquire a decent radio to utilize this new antenna. I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. It is best to make the impedance matching adjustable, using switched transformation ratio. I chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 100W on a Wire Antenna - How far would it reach? Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. It is worth experimenting with its length also. Let me review the salient observations from the previous work. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). 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. 73! I suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. 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. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. My favorite SOTA antenna is the End-Fed Half Wave Antenna. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. After some internet research, I settled on making the former from a paint roller. The EFHW transformer box from outside. The photos above show a method that works fairly well. 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. Will there be the same performance for single band EFHWs? |k"^N>F.AnJkJsq'PV}o0I. IIRC they call it a "compensator". Instead, this shifts everything down and makes it very easy to tune 10m. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! 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. Thanks for your comments. (Tvir s tvbeszl gpek s kszlkek) Ksznm. 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.) 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. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. 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. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. The original coil is designed for low power portable applications. 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. Low SSN Why do most Hams find HF Radio so difficult? It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 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. A week or two later I started to notice an occasional knocking sound inside the house. I look at the end-fed as just an extreme example of an off-center-fed antenna. The results are presented below. The bridge than will measure zero voltage across the bridge, and the LED will turn off. 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. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. The antenna is up. Above, 3t on the primary delivers Gcore<0.002S. This is perhaps one of the most hotly debated rookie topics in. It requires a set distance to hang both ends of the antenna, and that is not always given. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. 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. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. This reveals we only need to compensate for the reactive component. 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. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The SWR results are as follows: Next, I started winding the transformer. . You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. If you really want to get the heat out, add some fins to the aluminum box. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. 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%. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Transmitting on 15 meters was impossible because of RF into the radio. 2 0 obj I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. I decided to play with this to see what I could accomplish. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Klubunknl folyamatos a tagfelvtel. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. How does this SWR meter works? Finally the tank circuits specification is complete, which is sown below. 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. 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. 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. It uses a coil as a compensation unit, and no counterpoise. Interpretation of S-Meter Noise Floor in HF Radio Receivers. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. = .000001 / 3868.88 Jim, do you mind if I add your email and my answer as a comment to the article? I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. 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??). An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. This will also be handling 100W. I would mention first its ease of installation. I assume you know the GNARC source for EFHW antennas. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Two layers of 1mil Kapton tape are placed over the winding. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. High Q, hence low loss. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. We do not know what the actual impedance will be at the end of the antenna radiator. The negative effects of local QRM on an, How does antenna radiation occur? It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). 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. 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. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. 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. 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. The coil is just 12 turns of wire wrapped around a 0.7 inch diameter tube, located about 6 feet past the antenna's feedpoint. I also will ask, why didnt it work for you. 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. High self-resonant frequency. Zin=46.52+j6.72. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. 2015. 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. The SWR was measured for each of the three antennas across the CW portion of the bands. Looking at several builds and discussions, such as commercial antennas (e.g. (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. 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. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. There are two aspects, however that we need to consider: Lets begin with the transformer. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. Thirty turns #28 are wound on the two FT114-43 cores. 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. I settled on a compact secondary using #28 wire. A week or two later I started to notice an occasional knocking sound inside the house. In this case, it looks important. 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). Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. 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. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. 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. Elnzst krnk, de elsikkadt az zenete. However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings. For . I was curious why this capacitor was added to the transformer. Why had I not noticed this before? At this point, I'm leaning towards the EFHW, but any of these antennas seem . This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . What kind of balun is this? The real power limit will be core heating. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. In theory, the examination is supposed to be used to help clarify your medical condition and . Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. I used the 14g enameled wire and wound it on the FT240-43. 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. I added some Christmas colored zip ties to hold everything in place. That is an end-fed, but very different then the half wave construction. 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. 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 last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. 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. We also need to know what are the frequencies or bands for which we plant to use this antenna. I can give a link if you need. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. No wire counterpoise is used to reproduce the SOTA setup. I installed a QRP SWR meter into the tuner that makes tuning very handy. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. i liked it a lot, you give good ideas, many thanks. 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. 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. 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. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. To further improve the flux linkage, I wound the primary on top of the secondary. Then I covered the coil in kapton tape to hold it together. The previous table already contains these measurements. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. That will be the missing resistor in the resistor bridge of the below circuit. Show more. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Your article was well written and very informative, thanks. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. This provides proper insulation from the relatively high voltages on the seconder winding. The combination of the transformer with the end-fed dipole results in a positive reactance. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. 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. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. On the transformer, I added a few wingnuts to tighten down the antenna wire. Do I count the six loops around the pvc in the measurement? So I built myself an improved replacement matching transformer. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 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. What are the advantages and disadvantages of the end-fed half wave antenna? Why had I not noticed this before? 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. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. I checked the wall brackets and mast, but all the fixings were nice and tight. It may be one or even five kilo-ohms. 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. These dimensions were derived from modelling the antenna in EZNEC. 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). It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. It is worth experimenting with its length also. What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Why does antenna radiation occur? Csatlakozz csapatunkhoz! I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. Best regards and thanks again for your comment. (LogOut/ Well, in ham radio, everything works. Your posting put it all together for meTHANK YOU!!!! Most of the time 5 to 20W will be adequate for activation anyway. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. This is typically a weak spot. 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 tests here were using a dummy load on the transformer, and that did allow confirmation of the design and expected loss at 3.6MHz. Basu Bhattacharya (VU2NSB). Basically, the loading coil is operating as a trap. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. So, I embarked on testing it for myself. Most informative and appreciated. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Just the bare 80m wire is shown in red. Also find news related to Efhw Compensation Coil Experiment which is trending today. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email.
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