The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The transformer fits sideways in the box with a few millimeters to spare. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. Z8Vq9_@x C\Agv#. I will go back and have the article corrected. . 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'. Does your station desperately need a good RF ground to behave properly? For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. For . This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. It may be one or even five kilo-ohms. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com The toroid with its many taps may be soldered directly on a multi-position switch. This is not an optimal value, benefit may be obtained by exploring small changes to that value. I tossed the line as far up as I could in a tree. I am planning to use this latest one at the Field Day next year. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. All Rights Reserved. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. It performed well on both the 2m and 70cm bands. But systems that work better increase the prospects of contacts. 3) Total losses are approximately independent of core volume. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Copyright 2014-2023. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. I decided to push for best efficiency with a 5-turn primary. It is all about getting the heat out. It is worth experimenting with its length also. For our transformer at 100W (==> 71 Vrms into 50 ) , the core cross section for the two FT114s is 0.74 cm2 , consider the lowest frequency as 3.5 MHz and our 5-turn primary, then plugging in the numbers we find Bmax = 0.012 T. Lets consider a much more challenging extreme: 1000W and the 160m band. You cant really see the antenna wire, but the red line shows the antenna path. I will publish my findings, but I cannot not promise to complete it until early fall. 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. From that we can find Mismatch Loss. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The antenna is effective and the materials and construction are of a very high quality. 73 I am currently working on measurements of an EFHW antenna. This antenna is working for 80,40,20,10 and 6m bands. . 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. The technical storage or access that is used exclusively for statistical purposes. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. Thanks in advance, good health for you in these times, However, it has its idiosyncrasies. i liked it a lot, you give good ideas, many thanks. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Firstly, bandwidth on 80m is restricted to about 80 kHz at . The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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? With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Next, I started winding the transformer. So far so good. 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. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. The biggest uncertainty in these measurements was the actual power level used. No capacitor was installed. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Of course, you will need to find your tuning positions and apply your own position scale. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency 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. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. 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. 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. Jim, do you mind if I add your email and my answer as a comment to the article? 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. 100W on a Wire Antenna - Is it good enough for DX? In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. 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. Highest frequency = 14.350 MHz. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The resistance (real) component of the impedance is right where we want it near 50 ohms. The photos above show a method that works fairly well. 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. First, note that the transformer has low transmission loss up to nearly 50MHz. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. 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. Consequently, this is how the capacitance values are determined. This reveals we only need to compensate for the reactive component. The cooling curve I measured is shown below. The Counterpoise is a short, typically one twentieth (0.05 *. ) I fashioned an antenna connector with washers made from some acrylic rod I had on hand. With no counterpoise wire it will be the coaxs shield providing it. Change). The computation method is also touched on. Not the ideal antenna, but convenient! I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. The difference here is that the target bands are low frequency. I checked the wall brackets and mast, but all the fixings were nice and tight. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. 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 recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. 100W on a Wire antenna! Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Transmitting on 15 meters was impossible because of RF into the radio. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? MyAntennas.com Group | When I'm measuring the half way point on my EFHW stream 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. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. If you stare at the above frequency sweeps you will discover a few things. The next important parameter is the parallel resonant circuits resonant frequency. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. Although it is simple to build and is a multiband antenna, it has several attributes that . In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. The antenna is effective and the materials and construction are of a very high quality. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. Thank you for an interesting and informative read. My favorite SOTA antenna is the End-Fed Half Wave Antenna. High self-resonant frequency. 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. Interpretation of S-Meter Noise Floor in HF Radio Receivers.