After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! Isn't it? Below is the schematic of the final build. 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. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Could it be something to do with the new vertical aerial I had recently installed? A 100pF silvered mica was connected in shunt with the transformer . The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Change), You are commenting using your Twitter account. VSWR<1.8 over all of HF. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. Two layers of 1mil Kapton tape are placed over the winding. 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 illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. 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. Why does antenna radiation occur? 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). ROB@COMCOIL.COM These dimensions were derived from modelling the antenna in EZNEC. Taking the time derivative of the above equation you get the power dissipation. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. I assume you know the GNARC source for EFHW antennas. 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. I can give a link if you need. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 100W on a Wire Antenna - How far would it reach? 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. 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. 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. 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. One end is about 5 meters high on an extended fishing pole. Compensation. 2015. Very interesting design. 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. (LogOut/ I installed a QRP SWR meter into the tuner that makes tuning very handy. . The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. 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. 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. 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. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. 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'. However, it has its idiosyncrasies. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 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. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. How far could it possibly reach? How big and where to place it is likely best determined empirically. Many people use an inductor placed at the near end to make things level out on the higher bands. 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'. Do I count the six loops around the pvc in the measurement? Some say you do not need a counterpoise, but that is false. Best regards and thanks again for your comment. 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 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. %PDF-1.4 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. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. There is lot of controversy around the EFHW antennas. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. 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 went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. The worse SWR was 1:1.7 at the top end of 20 meters. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. (LogOut/ It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. 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! 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. The next important parameter is the parallel resonant circuits resonant frequency. clear. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Thanks again Jim. For . 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. 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. The bridge than will measure zero voltage across the bridge, and the LED will turn off. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. You can see the coil in the picture below (red arrow). Be sure to take a look for additional analysis and conclusions. And now I am planning to build one for 160/80m. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. . I wish you lots of productive experimentations and successful portable operations. In his article, I will try to bust some of the myths associated with Inverted. 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. There is much more that can be written about this antenna and its matching, but that was not my aim. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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. 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. One point of my small-core, compact winding design was to be able to cool the core. 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. This can then, fed with coaxial cable, in many cases be . This will also be handling 100W. Im very pleased with that indeed. Lets do a quick calculation to see how much an issue is this output capacitance. Graphed with a log scale, it makes a nice straight line. 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. We use cookies to optimize our website and our service. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Looking at several builds and discussions, such as commercial antennas (e.g. Make sure the first wire is wrapped evenly around the whole toroid. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. 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. So, I embarked on testing it for myself. I would mention first its ease of installation. A ktelez mezket * karakterrel jelltk. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. Jim, do you mind if I add your email and my answer as a comment to the article? No capacitor was installed. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. For the last step, I put together a RF choke to use between the radio and the feedline. I found it very useful to label the tuner with switch and capacitance positions. The photos above show a method that works fairly well. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? Does your station desperately need a good RF ground to behave properly? Wow, Gary! This provides proper insulation from the relatively high voltages on the seconder winding. Most of the time 5 to 20W will be adequate for activation anyway. This gave me an effective coil diameter of 40.5mm. These four data points are plotted on the Transmission Losses chart shown below as the yellow squares, all but the 80 meter point coming in a bit lower than expected losses based on the VNA measurements. A 100pF silvered mica was connected in shunt with the transformer primary. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. Let us touch on some necessary theory to begin with. 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). This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Will there be the same performance for single band EFHWs? 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. The antenna is up. 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? On the transformer, I added a few wingnuts to tighten down the antenna wire. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. All Rights Reserved. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. I am building an EFHW antenna for my new. Which begs the question what happens when you attach the antenna? This will yield the minimal capacitance of the variable capacitor. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. Can a diode be used to rectify signals smaller than its threshold voltage? The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. The final turns ratio turned out to be 3:29. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. 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 depends on the selection of the inductance and the capacitor values. This antenna is only 15m long using 2 loading coils. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. 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 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. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. 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. The equation should have a 10^6 and not 10^-6 in the nominator. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. stream I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? My favorite SOTA antenna is the End-Fed Half Wave Antenna. 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. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. The Counterpoise is a short, typically one twentieth (0.05 *. ) I look at the end-fed as just an extreme example of an off-center-fed antenna. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. 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. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. The real power limit will be core heating. 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. Change), You are commenting using your Facebook account. 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. 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 dont have an amplifier, so only need to be able to handle 100W. Let me review the salient observations from the previous work. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. (LogOut/ 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. No wire counterpoise is used to reproduce the SOTA setup. To further improve the flux linkage, I wound the primary on top of the secondary. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. So, how to construct an end-fed half wave antenna? This will yield the maximum capacity of the variable capacitor. The latest news about Efhw Compensation Coil Experiment. Not the ideal antenna, but convenient! Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. Understanding Antennas The Good, the Bad, and the Ugly. 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. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. This article will not address that antenna type. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. I used four parallel #28 wires (not twisted) for the primary.

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