As is often the case, packaging was determined by what boxes I had laying around. Most informative and appreciated. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Make sure the first wire is wrapped evenly around the whole toroid. 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. It does not need any special components; in fact, most of us may have them in our shack drawers already. The biggest uncertainty in these measurements was the actual power level used. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. How big and where to place it is likely best determined empirically. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. The highest voltages as well as radiation are also at the end of the antenna wire. 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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. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Note: If we change the primary number of turns, the impedance ratios will considerable change also. 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 assume you know the GNARC source for EFHW antennas. Show more. 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. 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. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. I first mounted the SO239 connector to the box. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Some say you do not need a counterpoise, but that is false. 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. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. I particularly want to know how counterpoise affects the common mode currents on the coax. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. What kind of balun is this? 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. 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. This will yield the minimal capacitance of the variable capacitor. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Why does antenna radiation occur? Well, in ham radio, everything works. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. This is not an optimal value, benefit may be obtained by exploring small changes to that value. 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. 2006. It is recommended to use at least 2W non-inductive resistors for this purpose. The model results show the need for a not entirely insignificant counterpoise. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. 73 100W on a Wire Antenna - How far would it reach? Thank you Gary. Could it be something to do with the new vertical aerial I had recently installed? Looking at several builds and discussions, such as commercial antennas (e.g. 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. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. 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. The computation method is also touched on. The real power limit will be core heating. 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 ROB@COMCOIL.COM Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. No capacitor was installed. The bridge than will measure zero voltage across the bridge, and the LED will turn off. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The photos above show a method that works fairly well. My question is what is 'higher frequency' specifically? The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. Why had I not noticed this before? From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. The SWR for the 20 meter EFHW antenna was < 1.2:1 A week or two later I started to notice an occasional knocking sound inside the house. 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. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. 2015. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Lowest frequency = 7.000 MHz. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Ismerje meg a hozzszls adatainak feldolgozst . This is perhaps one of the most hotly debated rookie topics in. 73! This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Your article was well written and very informative, thanks. Although it is simple to build and is a multiband antenna, it has several attributes that . In comparison to the EFHW antenna, a simple dipole offers a far better prospect. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. I used four parallel #28 wires (not twisted) for the primary. How does this SWR meter works? A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. IIRC they call it a "compensator". Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. This suggests an inductive reactance. Below about 7 MHz, transmission losses increase as the core temperature increases. % View the job description, responsibilities and qualifications for this position. The equation in the article is corrected now. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Change), You are commenting using your Facebook account. Very interesting design. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Lowest measured inductivity = 2.0 H. 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%. I tossed the line as far up as I could in a tree. First, note that the transformer has low transmission loss up to nearly 50MHz. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I dont have an amplifier, so only need to be able to handle 100W. 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. 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). Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. coil inductance calculator at 66pacific.com. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. 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. Most of the time 5 to 20W will be adequate for activation anyway. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. It depends on the selection of the inductance and the capacitor values. Thank you for an interesting and informative read. 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. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. More designs can be found by Googling "80m loaded dipole.". 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. Is it any good? Trapped five band EFHW SOTA antenna. This article will not address that antenna type. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Jim, do you mind if I add your email and my answer as a comment to the article? One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Just the bare 80m wire is shown in red. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. It is worth experimenting with its length also. As I reexamined my formula, you pointed it out correctly, there is an error in it. 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. I settled on a compact secondary using #28 wire. 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. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Impressive article and so well done that I may give it a try. Could it be something to do with the new vertical aerial I had recently installed? The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. It is all about getting the heat out. Hence, we need to move along and start to include the antenna with our testing. = .00 00 00 00 0 258 Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. You cant really see the antenna wire, but the red line shows the antenna path. 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. And not all hf antenna installation are same, with most requiring bit of tinkering. We use cookies to optimize our website and our service. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. We need to measure the inductances of the toroid with the tapped coil. 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. Which begs the question what happens when you attach the antenna? 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. And of course, a counterpoise with various lengths. The antenna is effective and the materials and construction are of a very high quality. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. We also need to know what are the frequencies or bands for which we plant to use this antenna. 100W on a Wire Antenna How far would it reach? You can see the coil in the picture below (red arrow). The antennas are set up as a sloper as in my SOTA outings. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Look at the compensation coil slide. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? 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. In an urban area we are much more restricted, especially if we need to be stealth about it. 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. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. . It is important that resonance may be achieved at each tap of the inductance. Interpretation of S-Meter Noise Floor in HF Radio Receivers. Above is a thermograph of the transformer at 20W input at 3.6MHz. Copyright 2014-2023. By using traps, the antenna works on all three bands with no operator interaction. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. 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. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. 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. How badly can high Local Ambient QRM affect HF Radio? Not the ideal antenna, but convenient! (LogOut/ 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. Looking at several builds and discussions, such as commercial antennas (e.g. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The technical storage or access that is used exclusively for anonymous statistical purposes. Can you give me an idea for your 100 W version, you built for 80/60/40 m. It performed well on both the 2m and 70cm bands. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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? The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Regards VE9HAM. 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. Some website features may not function optimally without cookies. 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. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. |k"^N>F.AnJkJsq'PV}o0I. Check your inbox or spam folder to confirm your subscription. The resistance (real) component of the impedance is right where we want it near 50 ohms. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. 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. 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. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. 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.
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