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. : I see you were able to post your comment now, so I just copied my email answer here for others to see. It depends on the selection of the inductance and the capacitor values. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. 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. This will yield the minimal capacitance of the variable capacitor. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. 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. 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). 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. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. 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. Although it is simple to build and is a multiband antenna, it has several attributes that . I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). The Counterpoise is a short, typically one twentieth (0.05 *. ) It is important that resonance may be achieved at each tap of the inductance. The antennas are set up as a sloper as in my SOTA outings. I am building an EFHW antenna for my new. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. nanoVNA-H can firmware be updated if it has a broken USB socket? During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. 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. The model results show the need for a not entirely insignificant counterpoise. 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. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. The results are shown below. For a quarter wave that is about 8 nS. It may be one or even five kilo-ohms. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. The results are presented below. Instead, this shifts everything down and makes it very easy to tune 10m. This gave me an effective coil diameter of 40.5mm. 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. The resistance (real) component of the impedance is right where we want it near 50 ohms. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. So I built myself an improved replacement matching transformer. 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. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. And not all hf antenna installation are same, with most requiring bit of tinkering. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. I needed to add an additional coil (approx 12.5 uH) about . Thanks again Jim. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. The highest frequency could be14.350MHz. Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . From that we can find Mismatch Loss. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Why does antenna radiation occur? Workers' Comp. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. In this case, it looks important. 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. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. 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. (LogOut/ 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. No wire counterpoise is used to reproduce the SOTA setup. If you stare at the above frequency sweeps you will discover a few things. No capacitor was installed. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. 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. In his article, I will try to bust some of the myths associated with Inverted. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. What are its disadvantages? High Q, hence low loss. % I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. It is all about getting the heat out. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. I mounted the transformer on a tree for testing. 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. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. I found it very useful to label the tuner with switch and capacitance positions. 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. 100W on a Wire Antenna - Is it good enough for DX? Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. It is worth experimenting with its length also. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. With no counterpoise wire it will be the coaxs shield providing it. I wish I had a simple answer, but really this is where some experimentation can pay off. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. clear. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). Zin=46.52+j6.72. Elnzst krnk, de elsikkadt az zenete. 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??). It performed well on both the 2m and 70cm bands. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. There are two aspects, however that we need to consider: Lets begin with the transformer. It does not need any special components; in fact, most of us may have them in our shack drawers already. This will yield the maximum capacity of the variable capacitor. 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. Krem, rja le, mi a krdse. The negative effects of local QRM on an, How does antenna radiation occur? = 258 * 10^-12. All Rights Reserved. 2015. The technical storage or access that is used exclusively for statistical purposes. Isn't it? . 3) Total losses are approximately independent of core volume. You can start with the links below. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Compensation. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. One possible explanation is that the core losses drop with temperature. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Thanks in advance, good health for you in these times, Wow, Gary! VK1OD.net (offline). 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. 2 0 obj 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. The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. I assume you know the GNARC source for EFHW antennas. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. Look at the compensation coil slide. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. Some hams swear by them, yet some completely demean it. 2. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. I decided to play with this to see what I could accomplish. Below about 7 MHz, transmission losses increase as the core temperature increases. (LogOut/ The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. 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. The original coil is designed for low power portable applications. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. 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? 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. This reveals we only need to compensate for the reactive component. A week or two later I started to notice an occasional knocking sound inside the house. How badly can high Local Ambient QRM affect HF Radio? To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. Trapped five band EFHW SOTA antenna. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. Thanks for your comments. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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. ROB@COMCOIL.COM The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. Why had I not noticed this before? There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Of course, you will need to find your tuning positions and apply your own position scale. Transmitting on 15 meters was impossible because of RF into the radio. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. It is not necessary to calculate the above; the results are sown in the following table. Above is a sweep of the uncompensated prototype with a 3220+50 load. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. Nagyon j ez a cikk. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Thanks! The wire as I strung it up seemed to resist having a good SWR for the 20m band. application of Kirchhoff's current Law on a typical EFHW antenna configuration. However, it has its idiosyncrasies. I used the 14g enameled wire and wound it on the FT240-43. I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. For . So far so good. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. Im very happy with the result. 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. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. However, a key restriction is its 25W power rating, due to the small matching transformer. It will present its parameters, so anybody with basic home-brew skills will be able to build it. The basic question before us is how does an antenna work? 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. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. 73! 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. Why had I not noticed this before? Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). Lowest measured inductivity = 2.0 H. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Jos van den Helm's (PA1ZP) article published in Radcom: Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. 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. 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. We use cookies to optimize our website and our service. 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. Ive spent some time on digital modes over the last week and and my signal reports seem very similar to the pre-80m-extension period, which is good, and I am getting out well past 1000 miles on 20, 40m and 80m digital. 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. Let us touch on some necessary theory to begin with. Two layers of 1mil Kapton tape are placed over the winding. There is much more that can be written about this antenna and its matching, but that was not my aim. Graphed with a log scale, it makes a nice straight line. A 100pF silvered mica was connected in shunt with the transformer primary. The next important parameter is the parallel resonant circuits resonant frequency. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. Subscribe to our newsletter and receive regular updates on new posts and articles. I checked the wall brackets and mast, but all the fixings were nice and tight. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. I ran WSPR at 10mW for about 2 hours and got the results below. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. 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. Note: If we change the primary number of turns, the impedance ratios will considerable change also. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. I first mounted the SO239 connector to the box. I particularly want to know how counterpoise affects the common mode currents on the coax. 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. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! I would mention first its ease of installation. The difference here is that the target bands are low frequency. 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. 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. 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. Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. 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). Check your inbox or spam folder to confirm your subscription. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 100W on a Wire Antenna How far would it reach? 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. There are many good descriptions on the net about this type of antenna. Current Balun 1. Basu Bhattacharya (VU2NSB). I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Proudly created withWix.com. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. 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. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. The original coil is designed for low power portable applications. stream xZ
Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! It is important to consider the voltages on this tank circuit. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 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 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. 100W on a Wire antenna! It is best to make the impedance matching adjustable, using switched transformation ratio. And of course, a counterpoise with various lengths. Also find news related to Efhw Compensation Coil Experiment which is trending today. 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. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. Thank you for your comment and feedback on the article about the EFHW antenna. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. More designs can be found by Googling "80m loaded dipole.". 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. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. Is FT8 popularity growing at the cost of SSB Phone and CW? 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. Even at 15W the voltage at the ends may reach 100-200V. 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 antenna is only 15m long using 2 loading coils. (LogOut/ 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. The cooling curve I measured is shown below. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. On the transformer, I added a few wingnuts to tighten down the antenna wire. 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. First, note that the transformer has low transmission loss up to nearly 50MHz. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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.