(Tvir s tvbeszl gpek s kszlkek) Ksznm. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. It is not necessary to calculate the above; the results are sown in the following table. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. 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. How badly can high Local Ambient QRM affect HF Radio? The SWR was measured for each of the three antennas across the CW portion of the bands. Which begs the question what happens when you attach the antenna? The antenna is effective and the materials and construction are of a very high quality. 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. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. Now I just need to build or acquire a decent radio to utilize this new antenna. Jim, do you mind if I add your email and my answer as a comment to the article? 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. The next important parameter is the parallel resonant circuits resonant frequency. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. Thank you Gary. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. 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. 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. 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. 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. How to get started on ISS Cross band Repeater? Subscribe to our newsletter and receive regular updates on new posts and articles. Consequently, this is how the capacitance values are determined. The impedance matching circuit is essentially a simple parallel resonant LC circuit. This reveals we only need to compensate for the reactive component. Csatlakozz csapatunkhoz! Yes, indeed EFHW antennas are very useful for SOTA or other field operation. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. Look at the compensation coil slide. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. You can start with the links below. The parasitic reactances near the feed-point also vary between installations. 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. 73 However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. The technical storage or access that is used exclusively for anonymous statistical purposes. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The antenna is effective and the materials and construction are of a very high quality. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. It will present its parameters, so anybody with basic home-brew skills will be able to build it. 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. . You cant really see the antenna wire, but the red line shows the antenna path. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. On the transformer, I added a few wingnuts to tighten down the antenna wire. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. 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. 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. 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. 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. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. 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. For the last step, I put together a RF choke to use between the radio and the feedline. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Most informative and appreciated. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. To be safe, better not get much above 120 C. I mounted the transformer on a tree for testing. This is perhaps one of the most hotly debated rookie topics in. 5) It is very hard to avoid stray capacitance on the output. Klubunknl folyamatos a tagfelvtel. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Many people use an inductor placed at the near end to make things level out on the higher bands. 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. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. 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 an urban area we are much more restricted, especially if we need to be stealth about it. Below is the schematic of the final build. = .00 00 00 00 0 258 Im very happy with the result. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Research salary, company info, career paths, and top skills for Software Engineer - EDI 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). clear. 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. One way or another there is always a counterpoise involved if the antenna is tuned correctly. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Thank you for an interesting and informative read. Hello, a wonderful approach for the problems.. 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 wire as I strung it up seemed to resist having a good SWR for the 20m band. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Regards VE9HAM. P.S. '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. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. I also will ask, why didnt it work for you. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. How far could it possibly reach? Below about 7 MHz, transmission losses increase as the core temperature increases. You can see the coil in the picture below (red arrow). It performed well on both the 2m and 70cm bands. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. 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). The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. We use cookies to optimize our website and our service. Does your station desperately need a good RF ground to behave properly? Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Looking at several builds and discussions, such as commercial antennas (e.g. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Z8Vq9_@x C\Agv#. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. 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. 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. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? In his article, I will try to bust some of the myths associated with Inverted. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. The original coil is designed for low power portable applications. The toroid with its many taps may be soldered directly on a multi-position switch. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. 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. I wish I had a simple answer, but really this is where some experimentation can pay off. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). 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. of the wavelength. Basu Bhattacharya (VU2NSB). 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. One point of my small-core, compact winding design was to be able to cool the core. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. At this point, I'm leaning towards the EFHW, but any of these antennas seem . 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" 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. 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. With such a switch, it is impossible to forget to switch back to operational mode. Let me review the salient observations from the previous work. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. I would mention first its ease of installation. 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. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. Why does antenna radiation occur? It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 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.) When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Ismerje meg a hozzszls adatainak feldolgozst . The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Show more. 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. To further improve the flux linkage, I wound the primary on top of the secondary. View the job description, responsibilities and qualifications for this position. 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 He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. Highest frequency = 14.350 MHz. I decided to push for best efficiency with a 5-turn primary. The results are shown below. The overlaid VSWR plots are shown below. 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. This article will not address that antenna type. 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. Compensation. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. 100W on a Wire Antenna - How far would it reach? A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. 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. Frank VK1VK. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. The combination of the transformer with the end-fed dipole results in a positive reactance. I tossed the line as far up as I could in a tree. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. 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. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. From that we can find Mismatch Loss. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. The EFHW transformer box from outside. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Change), You are commenting using your Twitter account. 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. Be cautious, such voltages may cause a quite painful skin scorch. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. And not all hf antenna installation are same, with most requiring bit of tinkering. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. 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'. With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. Lowest measured inductivity = 2.0 H. Just the bare 80m wire is shown in red. 100W on a Wire antenna! 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. It uses a coil as a compensation unit, and no counterpoise. The final turns ratio turned out to be 3:29. 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. One possible explanation is that the core losses drop with temperature. 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. I can give a link if you need. Taking the time derivative of the above equation you get the power dissipation. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. 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. Your article was well written and very informative, thanks. |k"^N>F.AnJkJsq'PV}o0I. Above 7MHz, there is very little temperature dependence at all. 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. 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??). 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Firstly, bandwidth on 80m is restricted to about 80 kHz at . This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. 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. 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. IIRC they call it a "compensator". I am currently working on measurements of an EFHW antenna. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. The band compensating inductor placed on the wire is another story. 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). 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 Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. Can a diode be used to rectify signals smaller than its threshold voltage? Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. 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. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! However, it has its idiosyncrasies. 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. If you stare at the above frequency sweeps you will discover a few things. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. A week or two later I started to notice an occasional knocking sound inside the house. It does not need any special components; in fact, most of us may have them in our shack drawers already. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Hence, there is no optimum single-fit solution. I assume you know the GNARC source for EFHW antennas. Thirty turns #28 are wound on the two FT114-43 cores. This suggests an inductive reactance. 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 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. The SWR figures were as follows: FT240-43 132ft/100pF capacitor . Why had I not noticed this before? High self-resonant frequency. The highest voltages as well as radiation are also at the end of the antenna wire. I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. I added some Christmas colored zip ties to hold everything in place. The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. Above is a sweep of the roughly compensated transformer. This is typically a weak spot. Trapped five band EFHW SOTA antenna. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. All Rights Reserved. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former.