I found it very useful to label the tuner with switch and capacitance positions. 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. Lets call this element the LoadAttenuator. Can a diode be used to rectify signals smaller than its threshold voltage? There are many good descriptions on the net about this type of antenna. Trapped five band EFHW SOTA antenna | VK3IL Blog This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. So, how to construct an end-fed half wave antenna? As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. The basic question before us is how does an antenna work? The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. Two layers of 1mil Kapton tape are placed over the winding. How badly can high Local Ambient QRM affect HF Radio? A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. EFHW Antenna Frequency Compensation Lead - YouTube I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). It performed well on both the 2m and 70cm bands. How does this SWR meter works? I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Will there be the same performance for single band EFHWs? With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. My design objectives were: 1. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. The Counterpoise is a short, typically one twentieth (0.05 *. ) = 1/30.e6 = 33 nS. 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. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. Wrap the first wire around the toroid 27 times (I used a black wire for this). You can start with the links below. % It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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 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. 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 my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! The results are shown below. 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. 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. 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. 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. The EFHW transformer box from outside. Z8Vq9_@x C\Agv#. The computation method is also touched on. Pocket-tenna core is finally done! Wire and compensation coil being 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. 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??). 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 five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. It is best to make the impedance matching adjustable, using switched transformation ratio. Thanks again Jim. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). I am currently working on measurements of an EFHW antenna. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. Hence, we need to move along and start to include the antenna with our testing. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. The highest frequency could be14.350MHz. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. How far could it possibly reach? 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. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. 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. For the last step, I put together a RF choke to use between the radio and the feedline. 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. Not the ideal antenna, but convenient! Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. By using traps, the antenna works on all three bands with no operator interaction. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Does your station desperately need a good RF ground to behave properly? 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). 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. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. The impedance matching circuit is essentially a simple parallel resonant LC circuit. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. EFHW Compensation Coil Experiment - YouTube Next, I started winding 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. Most of the time 5 to 20W will be adequate for activation anyway. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Graphed with a log scale, it makes a nice straight line. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? It is worth experimenting with its length also. I assume you know the GNARC source for EFHW antennas. 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. Klubunknl folyamatos a tagfelvtel. Can I get away with no capacitor in my design? The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. This antenna is working for 80,40,20,10 and 6m bands. It is important that resonance may be achieved at each tap of the inductance. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? 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. Is it any good? Although it is simple to build and is a multiband antenna, it has several attributes that . Finally the tank circuits specification is complete, which is sown below. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 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 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. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Regards VE9HAM. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. 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. 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. Above is a sweep of the roughly compensated transformer. 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. 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. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Cmzett: Weince joseph How can we help? 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. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. The SWR was measured for each of the three antennas across the CW portion of the bands. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Above, 3t on the primary delivers Gcore<0.002S. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. 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 SWR for the 20 meter EFHW antenna was < 1.2:1 (LogOut/ 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. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. This suggests an inductive reactance. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. application of Kirchhoff's current Law on a typical EFHW antenna configuration. To be safe, better not get much above 120 C. 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. The Truth, ,and Nothing But The Truth (as I've experienced it) 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. Hi Ajai, Be sure to take a look for additional analysis and conclusions. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. The photos above show a method that works fairly well. Consequently, this is how the capacitance values are determined. The results are presented below. 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. A 100pF silvered mica was connected in shunt with the transformer primary. 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. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The previous table already contains these measurements. This will also be handling 100W. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. I look at the end-fed as just an extreme example of an off-center-fed antenna. P.S. 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. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency
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