The computation method is also touched on. Graphed with a log scale, it makes a nice straight line. 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. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 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 . 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. Hence, we need to move along and start to include the antenna with our testing. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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. Show more. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. It is not necessary to calculate the above; the results are sown in the following table. 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. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Could it be something to do with the new vertical aerial I had recently installed? However, a key restriction is its 25W power rating, due to the small matching transformer. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. Start by wrapping the wire around the toroid. This article will not address that antenna type. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Be cautious, such voltages may cause a quite painful skin scorch. But systems that work better increase the prospects of contacts. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. I particularly want to know how counterpoise affects the common mode currents on the coax. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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. Lowest measured inductivity = 2.0 H. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. Most informative and appreciated. What are the advantages and disadvantages of the end-fed half wave antenna? Firstly, bandwidth on 80m is restricted to about 80 kHz at . . Regards VE9HAM. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. Understanding Antennas The Good, the Bad, and the Ugly. 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. 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. A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. The results are shown below. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH Krem, rja le, mi a krdse. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. I am building an EFHW antenna for my new. It will present its parameters, so anybody with basic home-brew skills will be able to build it. 100W on a Wire Antenna - How far would it reach? 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. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. of the wavelength. Compensation. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 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. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. Just the bare 80m wire is shown in red. 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. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. For . I checked the wall brackets and mast, but all the fixings were nice and tight. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). To further improve the flux linkage, I wound the primary on top of the secondary. It is recommended to use at least 2W non-inductive resistors for this purpose. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. I first mounted the SO239 connector to the box. It depends on the selection of the inductance and the capacitor values. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. The model results show the need for a not entirely insignificant counterpoise. 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. Thanks! I then added two 220pf capacitors in series between the center conductor and ground. I then used a piece of heat shrink on the outside to hold everything in place. 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. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. It is not necessary to calculate the above; the results are sown in the following table. 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. 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. The results are presented below. It is clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. Hi Ajai, I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. 100W on a Wire Antenna How far would it reach? Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. If you stare at the above frequency sweeps you will discover a few things. Thanks again Jim. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. The photos above show a method that works fairly well. 100W on a Wire antenna! To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. 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. Make sure the first wire is wrapped evenly around the whole toroid. I checked the wall brackets and mast, but all the fixings were nice and tight. Instead, this shifts everything down and makes it very easy to tune 10m. As is often the case, packaging was determined by what boxes I had laying around. Will there be the same performance for single band EFHWs? The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. Below about 7 MHz, transmission losses increase as the core temperature increases. On the transformer, I added a few wingnuts to tighten down the antenna wire. Hence, there is no optimum single-fit solution. 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. However, a key restriction is its 25W power rating, due to the small matching transformer. First, note that the transformer has low transmission loss up to nearly 50MHz. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. = .000001 / 3868.88 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. 2015. 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. 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. High Q, hence low loss. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! 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. Can I get away with no capacitor in my design? I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. It is best to make the impedance matching adjustable, using switched transformation ratio. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Subscribe to our newsletter and receive regular updates on new posts and articles. 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. It performed well on both the 2m and 70cm bands. It uses a coil as a compensation unit, and no counterpoise. The equation in the article is corrected now. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. The wire as I strung it up seemed to resist having a good SWR for the 20m band. Apply for the Job in Software Engineer - EDI at St. Louis, MO. 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. The antenna is effective and the materials and construction are of a very high quality. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? I needed to add an additional coil (approx 12.5 uH) about . The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. Next, I started winding the transformer. Hello, a wonderful approach for the problems.. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Current Balun 1. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. I am currently working on measurements of an EFHW antenna. Which begs the question what happens when you attach the antenna? 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. Im very happy with the result. 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. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. The negative effects of local QRM on an, How does antenna radiation occur? Looking at several builds and discussions, such as commercial antennas (e.g. One possible explanation is that the core losses drop with temperature. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. A ktelez mezket * karakterrel jelltk. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. stream Copyright 2014-2023. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Is FT8 popularity growing at the cost of SSB Phone and CW? 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. You cant really see the antenna wire, but the red line shows the antenna path. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. This will yield the maximum capacity of the variable capacitor. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The biggest uncertainty in these measurements was the actual power level used. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Well, in ham radio, everything works. This is not an optimal value, benefit may be obtained by exploring small changes to that value. 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. I use shock cord to connect the insulator at the end of the wire to my fence. To be safe, better not get much above 120 C. Note: If we change the primary number of turns, the impedance ratios will considerable change also. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). It is very hard to know what will be the best solution for a given antenna installation if you want to hit all of the bands exactly. 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. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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. Research salary, company info, career paths, and top skills for Software Engineer - EDI After some internet research, I settled on making the former from a paint roller. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The cooling curve I measured is shown below. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. These dimensions were derived from modelling the antenna in EZNEC. Your article was well written and very informative, thanks. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. 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. 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. We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. Some hams swear by them, yet some completely demean it. Csatlakozz csapatunkhoz! The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. 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. Impressive article and so well done that I may give it a try. Above is a sweep of the roughly compensated transformer. 73 The previous table already contains these measurements. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Change), You are commenting using your Facebook account. 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. 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. Why had I not noticed this before? Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. Nagyon j ez a cikk. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. I tossed the line as far up as I could in a tree. Thank you for an interesting and informative read. I assume you know the GNARC source for EFHW antennas. (LogOut/ . Highest frequency = 14.350 MHz. 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. Thank you Gary. I installed a QRP SWR meter into the tuner that makes tuning very handy. In an urban area we are much more restricted, especially if we need to be stealth about it. Can a diode be used to rectify signals smaller than its threshold voltage? If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. I mounted the transformer on a tree for testing. I found it very useful to label the tuner with switch and capacitance positions. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. 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. Best regards and thanks again for your comment. The real power limit will be core heating. View the job description, responsibilities and qualifications for this position. 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. Thirty turns #28 are wound on the two FT114-43 cores. I decided to play with this to see what I could accomplish. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. No wire counterpoise is used to reproduce the SOTA setup. In his article, I will try to bust some of the myths associated with Inverted. Above is a sweep of the uncompensated prototype with a 3220+50 load. 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??). 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. They will be adjusted for resonance at or close to the CW portion of the bands. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF