. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. I added some Christmas colored zip ties to hold everything in place. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. Some say you do not need a counterpoise, but that is false. The combination of the transformer with the end-fed dipole results in a positive reactance. The next important parameter is the parallel resonant circuits resonant frequency. Your article was well written and very informative, thanks. Will there be the same performance for single band EFHWs? A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. The results are shown below. Elnzst krnk, de elsikkadt az zenete. 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. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. 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. I decided to play with this to see what I could accomplish. 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. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. The results are presented below. 73 Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. From that we can find Mismatch Loss. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. 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. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment 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. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. This article will not address that antenna type. How does this SWR meter works? One end is about 5 meters high on an extended fishing pole. The original coil is designed for low power portable applications. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. See the table above. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. 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. To further improve the flux linkage, I wound the primary on top of the secondary. It is not necessary to calculate the above; the results are sown in the following table. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. The technical storage or access that is used exclusively for statistical purposes. It performed well on both the 2m and 70cm bands. Low SSN Why do most Hams find HF Radio so difficult? It is recommended to use at least 2W non-inductive resistors for this purpose. 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. It will present its parameters, so anybody with basic home-brew skills will be able to build it. As you look to use this transformer at higher power levels, I can imagine that the bottleneck might be voltage breakdown or corona in the windings. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 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. 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. High Q, hence low loss. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. It is important to consider the voltages on this tank circuit. It not a loading coil. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Throw one end of the antenna wire, extended with a rope, as high as you can on a three, and walk away with the other end and attach it to the tuner. P.S. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! 2 0 obj Transmitting on 15 meters was impossible because of RF into the radio. Workers' Comp. For the last step, I put together a RF choke to use between the radio and the feedline. Below is the schematic of the final build. 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. 5) It is very hard to avoid stray capacitance on the output. Lowest frequency = 7.000 MHz. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Looking at several builds and discussions, such as commercial antennas (e.g. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! The smallest number I measured was 1.6 pF, derived from the self-resonance at 41 MHz with the leakage inductance (measured at 198 nH) when the secondary was shorted. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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. 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. Compensation. Above is a thermograph of the transformer at 20W input at 3.6MHz. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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. More designs can be found by Googling "80m loaded dipole.". This antenna is working for 80,40,20,10 and 6m bands. So, I embarked on testing it for myself. Hello, a wonderful approach for the problems.. Thanks in advance, good health for you in these times, First, note that the transformer has low transmission loss up to nearly 50MHz. The antenna is effective and the materials and construction are of a very high quality. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. It requires a set distance to hang both ends of the antenna, and that is not always given. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. Klubunknl folyamatos a tagfelvtel. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? 73! I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. Wow, Gary! In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. How badly can high Local Ambient QRM affect HF Radio? Finally the tank circuits specification is complete, which is sown below. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. I ran WSPR at 10mW for about 2 hours and got the results below. A week or two later I started to notice an occasional knocking sound inside the house. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. VK1OD.net (offline). 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. In his article, I will try to bust some of the myths associated with Inverted. If not a lightning strike, I will write an article about the experience as well. 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. I found it very useful to label the tuner with switch and capacitance positions. Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. Although it is simple to build and is a multiband antenna, it has several attributes that . 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. This will yield the maximum capacity of the variable capacitor. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Wrap the first wire around the toroid 27 times (I used a black wire for this). 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. This reveals we only need to compensate for the reactive component. The SWR was measured for each of the three antennas across the CW portion of the bands. 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. And of course, a counterpoise with various lengths. 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 other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. The 2 coils are 35uh and 90uh. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Understanding Antennas The Good, the Bad, and the Ugly. Thanks! Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. However, it has its idiosyncrasies. Consequently, this is how the capacitance values are determined. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Krem, rja le, mi a krdse. 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. One possible explanation is that the core losses drop with temperature. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Can you give me an idea for your 100 W version, you built for 80/60/40 m. 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. Current Balun 1. It does not need any special components; in fact, most of us may have them in our shack drawers already. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. It uses a coil as a compensation unit, and no counterpoise. The technical storage or access that is used exclusively for anonymous statistical purposes. 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. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. The EFHW transformer box from outside. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. 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. Can I get away with no capacitor in my design? 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. 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 checked the wall brackets and mast, but all the fixings were nice and tight. 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Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. 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. It is important that resonance may be achieved at each tap of the inductance. Not the ideal antenna, but convenient! 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 could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Start by wrapping the wire around the toroid. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. A radio station is as good or as bad as the antenna it has. See the second completed tuner depicted below. 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. 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. Hence, there is no optimum single-fit solution. The photos above show a method that works fairly well. This can then, fed with coaxial cable, in many cases be . And now I am planning to build one for 160/80m. The basic question before us is how does an antenna work? Thank you Gary. The equation in the article is corrected now. Csatlakozz csapatunkhoz! Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Research salary, company info, career paths, and top skills for Software Engineer - EDI Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. I assume you know the GNARC source for EFHW antennas. This will also be handling 100W. Highest frequency = 14.350 MHz. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). 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. It may be one or even five kilo-ohms. I particularly want to know how counterpoise affects the common mode currents on the coax. Zin=46.52+j6.72. We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. 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. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. As is often the case, packaging was determined by what boxes I had laying around. Z8Vq9_@x C\Agv#. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. The worse SWR was 1:1.7 at the top end of 20 meters. Frank VK1VK. 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. I then added two 220pf capacitors in series between the center conductor and ground. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. The negative effects of local QRM on an, How does antenna radiation occur? I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . The model results show the need for a not entirely insignificant counterpoise. Is it any good? The Counterpoise is a short, typically one twentieth (0.05 *. ) 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%. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. 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 - Is it good enough for DX? You can start with the links below. How big and where to place it is likely best determined empirically. Proudly created withWix.com. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. 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. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. There are two aspects, however that we need to consider: Lets begin with the transformer. 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. To be safe, better not get much above 120 C. Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern.