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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! The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Z8Vq9_@x C\Agv#. My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. What are the advantages and disadvantages of the end-fed half wave antenna? The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. 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. 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 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. 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. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! After some internet research, I settled on making the former from a paint roller. The results are presented below. Most of the time 5 to 20W will be adequate for activation anyway. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. 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). Then I covered the coil in kapton tape to hold it together. My design objectives were: 1. Subscribe to our newsletter and receive regular updates on new posts and articles. 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. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Make sure the first wire is wrapped evenly around the whole toroid. 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. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? I look at the end-fed as just an extreme example of an off-center-fed antenna. Thanks for your comments. (LogOut/ Thank you for an interesting and informative read. 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). 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. 73! During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. See the second completed tuner depicted below. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. Why does antenna radiation occur? I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Regards VE9HAM. Can you give me an idea for your 100 W version, you built for 80/60/40 m. High Q, hence low loss. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. Taking the time derivative of the above equation you get the power dissipation. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. And now I am planning to build one for 160/80m. Looking at several builds and discussions, such as commercial antennas (e.g. Looking at several builds and discussions, such as commercial antennas (e.g. 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. They will be adjusted for resonance at or close to the CW portion of the bands. 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. Best regards and thanks again for your comment. My favorite SOTA antenna is the End-Fed Half Wave Antenna. i liked it a lot, you give good ideas, many thanks. Check your inbox or spam folder to confirm your subscription. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. I checked the wall brackets and mast, but all the fixings were nice and tight. The worse SWR was 1:1.7 at the top end of 20 meters. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. Above, 3t on the primary delivers Gcore<0.002S. . Some website features may not function optimally without cookies. 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. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. of the wavelength. Will there be the same performance for single band EFHWs? I tossed the line as far up as I could in a tree. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. 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. 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. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. = .00 00 00 00 0 258 Current Balun 1. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. 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. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. The antenna is up. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. If you really want to get the heat out, add some fins to the aluminum box. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. I was curious why this capacitor was added to the transformer. Workers' Comp. 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. 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. IIRC they call it a "compensator". It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. We do not know what the actual impedance will be at the end of the antenna radiator. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. There are two aspects, however that we need to consider: Lets begin with the transformer. Be cautious, such voltages may cause a quite painful skin scorch. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Basu Bhattacharya (VU2NSB). Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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. Thanks again Jim. We need to measure the inductances of the toroid with the tapped coil. Let us touch on some necessary theory to begin with. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). Yes, indeed EFHW antennas are very useful for SOTA or other field operation. 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. The parasitic reactances near the feed-point also vary between installations. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. In the case of the EFHW 49:1 transformer, the major shortcomings of the most popular current designs are excessive leakage inductance and poor heat transfer from the ferrite material to the environment. 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. Also find news related to Efhw Compensation Coil Experiment which is trending today. 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 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. It is worth experimenting with its length also. 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. So, how to construct an end-fed half wave antenna? Highest frequency = 14.350 MHz. 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.