You can start with the links below. Most of the time 5 to 20W will be adequate for activation anyway. Could it be something to do with the new vertical aerial I had recently installed? . Lowest frequency = 7.000 MHz. This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. 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. 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 wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. A radio station is as good or as bad as the antenna it has. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. Next, I started winding the transformer. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. 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 is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. If you really want to get the heat out, add some fins to the aluminum box. 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'. The combination of the transformer with the end-fed dipole results in a positive reactance. The original coil is designed for low power portable applications. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. For . 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. 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). Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. Although it is simple to build and is a multiband antenna, it has several attributes that . We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. 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. I use shock cord to connect the insulator at the end of the wire to my fence. With such a switch, it is impossible to forget to switch back to operational mode. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. 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. Above, 3t on the primary delivers Gcore<0.002S. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Make sure the first wire is wrapped evenly around the whole toroid. The equation should have a 10^6 and not 10^-6 in the nominator. The difference here is that the target bands are low frequency. 100W on a Wire Antenna - Is it good enough for DX? But before we do, let us look at the insertion and transmission loss that the VNA is reporting. . Can I get away with no capacitor in my design? 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. Basically, the loading coil is operating as a trap. Thanks for your comments. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 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. 73! My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. Very interesting design. The total lenght is about 15mtr only and using 2 coils and a little stub (s) on the 80m coil or/and the 40m coil. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! In his article, I will try to bust some of the myths associated with Inverted. Even at 15W the voltage at the ends may reach 100-200V. The basic question before us is how does an antenna work? This antenna is working for 80,40,20,10 and 6m bands. 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. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. You can see the coil in the picture below (red arrow). Thanks in advance, good health for you in these times, Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. nanoVNA-H can firmware be updated if it has a broken USB socket? 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. 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. 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. (LogOut/ In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Lets do a quick calculation to see how much an issue is this output capacitance. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. 100W on a Wire antenna! Why does a wire carrying RF current radiates to produce EM waves which travel through, Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Could it be something to do with the new vertical aerial I had recently installed? Firstly, bandwidth on 80m is restricted to about 80 kHz at . This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Zin=46.52+j6.72. 3) Total losses are approximately independent of core volume. 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. 100W on a Wire Antenna - How far would it reach? To be safe, better not get much above 120 C. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. I wish you lots of productive experimentations and successful portable operations. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. It should be no surprise that 80pF is close to optimal. 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. 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. The impedance matching circuit is essentially a simple parallel resonant LC circuit. Which begs the question what happens when you attach the antenna? 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??). 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 is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. i liked it a lot, you give good ideas, many thanks. A week or two later I started to notice an occasional knocking sound inside the house. I used the 14g enameled wire and wound it on the FT240-43. 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. The photos above show a method that works fairly well. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The model results show the need for a not entirely insignificant counterpoise. For a quarter wave that is about 8 nS. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. The radiation pattern of this antenna on most bands produces multiple lobes. blue: 250pF, to much compensation. Refurbishing aluminium antenna parts affected by weather / corrosion. CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. 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. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. 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 permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Lets call this element the LoadAttenuator. This provides proper insulation from the relatively high voltages on the seconder winding. 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. IIRC they call it a "compensator". 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Many people use an inductor placed at the near end to make things level out on the higher bands. The overlaid VSWR plots are shown below. 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. Now I just need to build or acquire a decent radio to utilize this new antenna. As I reexamined my formula, you pointed it out correctly, there is an error in it. 2006. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. I checked the wall brackets and mast, but all the fixings were nice and tight. The equation in the article is corrected now. I am planning to use this latest one at the Field Day next year. 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. How badly can high Local Ambient QRM affect HF Radio? Show more. VSWR<1.8 over all of HF. After some internet research, I settled on making the former from a paint roller. Why had I not noticed this before? 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. The cooling curve I measured is shown below. 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. 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. 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. I decided to push for best efficiency with a 5-turn primary. I am building an EFHW antenna for my new. Some hams swear by them, yet some completely demean it. On the transformer, I added a few wingnuts to tighten down the antenna wire. I would mention first its ease of installation. Klubunknl folyamatos a tagfelvtel. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. Be aware counterpoise or ground radials are required for all hf antennas for better performance. 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. Taking the time derivative of the above equation you get the power dissipation. The aluminum box is the logical heatsink, so I cut a few scraps of aluminum to make a thermal connection to the bottom of the box and to the lid, adjusting with aluminum shims so that when the box lid is screw down, the entire thermal assembly, with the cores in the middle, is under a little compression. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. 100W on a Wire Antenna How far would it reach? 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. Nagyon j ez a cikk. = 258 * 10^-12. 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. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. I then used a piece of heat shrink on the outside to hold everything in place. 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. Elnzst krnk, de elsikkadt az zenete. 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. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . For the last step, I put together a RF choke to use between the radio and the feedline. They will be adjusted for resonance at or close to the CW portion of the bands. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. Current Balun 1. A ktelez mezket * karakterrel jelltk. 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. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. A week or two later I started to notice an occasional knocking sound inside the house. Some website features may not function optimally without cookies. The results are presented below. The Counterpoise is a short, typically one twentieth (0.05 *. ) Let us touch on some necessary theory to begin with. The SWR figures were as follows: FT240-43 132ft/100pF capacitor If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. The 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. Change), You are commenting using your Twitter account. Will there be the same performance for single band EFHWs? RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Note: If we change the primary number of turns, the impedance ratios will considerable change also. 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. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. What kind of balun is this? Most informative and appreciated. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The worse SWR was 1:1.7 at the top end of 20 meters. Why does antenna radiation occur? One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. 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. 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. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. 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. We use cookies to optimize our website and our service. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. This suggests an inductive reactance. 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. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. If not a lightning strike, I will write an article about the experience as well. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Apply for the Job in Software Engineer - EDI at St. Louis, MO. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. 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. I was curious why this capacitor was added to the transformer. High self-resonant frequency. Z8Vq9_@x C\Agv#. 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. It is important to consider the voltages on this tank circuit. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? You cant really see the antenna wire, but the red line shows the antenna path. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. The antenna is effective and the materials and construction are of a very high quality. The SWR was measured for each of the three antennas across the CW portion of the bands. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. Graphed with a log scale, it makes a nice straight line. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. It is worth experimenting with its length also. The results are shown below. 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). 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. |k"^N>F.AnJkJsq'PV}o0I. High Q, hence low loss. More designs can be found by Googling "80m loaded dipole.". 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. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Below about 7 MHz, transmission losses increase as the core temperature increases. A 100pF silvered mica was connected in shunt with the transformer 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%. Change), You are commenting using your Facebook account. So I built myself an improved replacement matching transformer. The computation method is also touched on. The toroid with its many taps may be soldered directly on a multi-position switch. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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 again Jim. Impressive article and so well done that I may give it a try. 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. The wire as I strung it up seemed to resist having a good SWR for the 20m band. This gave me an effective coil diameter of 40.5mm. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). % 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.

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