The photos above show a method that works fairly well. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. High self-resonant frequency. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Lets call this element the LoadAttenuator. It is best to make the impedance matching adjustable, using switched transformation ratio. In an urban area we are much more restricted, especially if we need to be stealth about it. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. I first mounted the SO239 connector to the box. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! This graphical depiction makes it easier to visualize the current and impedance correlation between bands. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? (Tvir s tvbeszl gpek s kszlkek) Ksznm. i liked it a lot, you give good ideas, many thanks. For . High Q, hence low loss. 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? At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Thanks for your comments. Engineering the EFHW 49:1 Transformer and Antenna For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Above, 3t on the primary delivers Gcore<0.002S. 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. Instead, this shifts everything down and makes it very easy to tune 10m. By using traps, the antenna works on all three bands with no operator interaction. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. 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. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Trapped five band EFHW SOTA antenna | VK3IL Blog The highest voltages as well as radiation are also at the end of the antenna wire. Also find news related to Efhw Compensation Coil Experiment which is trending today. It uses a coil as a compensation unit, and no counterpoise. Show more. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. How to tune a multi-band EFHW antenna using a loading coil 100W on a Wire Antenna How far would it reach? The antenna is effective and the materials and construction are of a very high quality. As is often the case, packaging was determined by what boxes I had laying around. Could it be something to do with the new vertical aerial I had recently installed? Let's find out! The End-Fed Half Wave Antenna a bit Differently The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. See the table above. 2 0 obj It performed well on both the 2m and 70cm bands. The worse SWR was 1:1.7 at the top end of 20 meters. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. The transformer fits sideways in the box with a few millimeters to spare. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. Lowest frequency = 7.000 MHz. 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. I particularly want to know how counterpoise affects the common mode currents on the coax. I needed to add an additional coil (approx 12.5 uH) about . It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. This reveals we only need to compensate for the reactive component. 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. ROB@COMCOIL.COM It is not necessary to calculate the above; the results are sown in the following table. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. I ran WSPR at 10mW for about 2 hours and got the results below. This provides proper insulation from the relatively high voltages on the seconder winding. What are the advantages and disadvantages of the end-fed half wave antenna? First, note that the transformer has low transmission loss up to nearly 50MHz. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. . This can then, fed with coaxial cable, in many cases be . Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. How big and where to place it is likely best determined empirically. PDF shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m 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. 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. 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. We use cookies to optimize our website and our service. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. The latest news about Efhw Compensation Coil Experiment. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. 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. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. If you really want to get the heat out, add some fins to the aluminum box. 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. I suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. 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. (LogOut/ 3) Total losses are approximately independent of core volume. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 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. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. 1. 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. Will there be the same performance for single band EFHWs? For a quarter wave that is about 8 nS. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Thank you for an interesting and informative read. Below about 7 MHz, transmission losses increase as the core temperature increases. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. Software Engineer - EDI - salary.com This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). AC Coil Replacement Cost 2023 - Forbes Home The SWR for the 20 meter EFHW antenna was < 1.2:1 Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. Z8Vq9_@x C\Agv#. Transmitting on 15 meters was impossible because of RF into the radio. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. 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. Impressive article and so well done that I may give it a try. The real power limit will be core heating. My question is what is 'higher frequency' specifically? 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. 5) It is very hard to avoid stray capacitance on the output. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Current Balun 1. 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. Does your station desperately need a good RF ground to behave properly? Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. 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. The antenna is up. In his article, I will try to bust some of the myths associated with Inverted. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com There is lot of controversy around the EFHW antennas. Make sure the first wire is wrapped evenly around the whole toroid. Simulating the end-fed half-wave (EFHW) dipole antenna The overall lenght is only 15m. My favorite SOTA antenna is the End-Fed Half Wave Antenna. The Counterpoise is a short, typically one twentieth (0.05 *. ) Then I covered the coil in kapton tape to hold it together. Subscribe to our newsletter and receive regular updates on new posts and articles. Hi Ajai, There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. 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 technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Above is a sweep of the roughly compensated transformer. Klubunknl folyamatos a tagfelvtel. 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. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Refurbishing aluminium antenna parts affected by weather / corrosion. 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. I will publish my findings, but I cannot not promise to complete it until early fall. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. 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. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. Best regards and thanks again for your comment. 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. Let us touch on some necessary theory to begin with. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. = 1/30.e6 = 33 nS. . (LogOut/ Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net Research salary, company info, career paths, and top skills for Software Engineer - EDI However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. A Smith chart view of EFHW transformer compensation Efhw Compensation Coil Experiment - Local Search Denver Post 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. Can you give me an idea for your 100 W version, you built for 80/60/40 m. Some hams swear by them, yet some completely demean it. Hello, a wonderful approach for the problems.. The parasitic reactances near the feed-point also vary between installations. 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. If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. 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 . You can start with the links below. Is FT8 popularity growing at the cost of SSB Phone and CW? A ktelez mezket * karakterrel jelltk. Look at the compensation coil slide. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration.