In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. Graphed with a log scale, it makes a nice straight line. 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. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC The cooling curve I measured is shown below. It not a loading coil. 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. = .000001 / 3868.88 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. It performed well on both the 2m and 70cm bands. . 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. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. Not the ideal antenna, but convenient! 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. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. I am planning to use this latest one at the Field Day next year. What are the advantages and disadvantages of the end-fed half wave antenna? And of course, a counterpoise with various lengths. First, note that the transformer has low transmission loss up to nearly 50MHz. Hence, there is no optimum single-fit solution. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. I use shock cord to connect the insulator at the end of the wire to my fence. 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. Let us touch on some necessary theory to begin with. 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??). used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Lets do a quick calculation to see how much an issue is this output capacitance. As is often the case, packaging was determined by what boxes I had laying around. 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. 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. Make sure the first wire is wrapped evenly around the whole toroid. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. (LogOut/ Jim, do you mind if I add your email and my answer as a comment to the article? (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . A Smith chart view of EFHW transformer compensation These dimensions were derived from modelling the antenna in EZNEC. We also need to know what are the frequencies or bands for which we plant to use this antenna. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I ran WSPR at 10mW for about 2 hours and got the results below. 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. Let me review the salient observations from the previous work. = .00 00 00 00 0 258 Independent Medical Evaluation - IME | Cynthia Hennessey The bridge than will measure zero voltage across the bridge, and the LED will turn off. 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. Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. With no counterpoise wire it will be the coaxs shield providing it. The computation method is also touched on. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. The transformer fits sideways in the box with a few millimeters to spare. 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. Best regards and thanks again for your comment. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. It performed well on both the 2m and 70cm bands. After some internet research, I settled on making the former from a paint roller. 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. 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. Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. nanoVNA-H can firmware be updated if it has a broken USB socket? With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. 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. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. 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. 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. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Trapped five band EFHW SOTA antenna | VK3IL Blog I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. ENDFED/EFHW Antenna & Choke - F5NPV - V85NPV You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. I look at the end-fed as just an extreme example of an off-center-fed antenna. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Start by wrapping the wire around the toroid. 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. 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. How big and where to place it is likely best determined empirically. It is worth experimenting with its length also. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. Transmitting on 15 meters was impossible because of RF into the radio. By using traps, the antenna works on all three bands with no operator interaction.
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