I then used a piece of heat shrink on the outside to hold everything in place. This article will not address that antenna type. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. Hello, a wonderful approach for the problems.. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. The SWR for the 20 meter EFHW antenna was < 1.2:1 How to get started on ISS Cross band Repeater? The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. 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. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. It performed well on both the 2m and 70cm bands. Consequently, this is how the capacitance values are determined. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. The real power limit will be core heating. The previous table already contains these measurements. To further improve the flux linkage, I wound the primary on top of the secondary. 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 found it very useful to label the tuner with switch and capacitance positions. Your article was well written and very informative, thanks. Looking at several builds and discussions, such as commercial antennas (e.g. Can you give me an idea for your 100 W version, you built for 80/60/40 m. This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. <> The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. And not all hf antenna installation are same, with most requiring bit of tinkering. 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. The resistance (real) component of the impedance is right where we want it near 50 ohms. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. As I reexamined my formula, you pointed it out correctly, there is an error in it. Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. It performed well on both the 2m and 70cm bands. Be sure to take a look for additional analysis and conclusions. The results are shown below. IIRC they call it a "compensator". The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. I first mounted the SO239 connector to the box. What are its disadvantages? In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings. I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. Instead, this shifts everything down and makes it very easy to tune 10m. Some website features may not function optimally without cookies. The next important parameter is the parallel resonant circuits resonant frequency. 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. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. I used four parallel #28 wires (not twisted) for the primary. 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. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. Workers' Comp. From that we can find Mismatch Loss. 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. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. Basically, the loading coil is operating as a trap. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. I decided to play with this to see what I could accomplish. Above is a sweep of the roughly compensated transformer. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. The technical storage or access that is used exclusively for statistical purposes. 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. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Low SSN Why do most Hams find HF Radio so difficult? The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. A week or two later I started to notice an occasional knocking sound inside the house. Subscribe to our newsletter and receive regular updates on new posts and articles. At this point, I'm leaning towards the EFHW, but any of these antennas seem . That is an end-fed, but very different then the half wave construction. A week or two later I started to notice an occasional knocking sound inside the house. 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 common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. This antenna is working for 80,40,20,10 and 6m bands. 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 does not need any special components; in fact, most of us may have them in our shack drawers already. The smallest number I measured was 1.6 pF, derived from the self-resonance at 41 MHz with the leakage inductance (measured at 198 nH) when the secondary was shorted. I will publish my findings, but I cannot not promise to complete it until early fall. The latest news about Efhw Compensation Coil Experiment. Lowest measured inductivity = 2.0 H. 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'. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. It is all about getting the heat out. 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. 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 basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. One possible explanation is that the core losses drop with temperature. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Frank VK1VK. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. But systems that work better increase the prospects of contacts. It uses a coil as a compensation unit, and no counterpoise. Which begs the question what happens when you attach the antenna? The comparison is done on 4 bands - 10m, 20m, 40, and 80m. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. I will go back and have the article corrected. The model results show the need for a not entirely insignificant counterpoise. 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. Im very pleased with that indeed. But I would caution its usage for higher power than 10-15W. By using traps, the antenna works on all three bands with no operator interaction. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Nagyon j ez a cikk. Wow, Gary! Isn't it? My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. But Ill find the error of my ways.and there are various on-line calculators to help me ensure I get the decimals and (H, mH, uH, pH, etc.) The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. 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. 100W on a Wire antenna! In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). Trapped five band EFHW SOTA antenna. Below is the schematic of the final build. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Next, I started winding the transformer. stream This will also be handling 100W. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. 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. 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. With such a switch, it is impossible to forget to switch back to operational mode. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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. Thanks for your comments. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. 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. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. 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. 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. 73 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. The results are presented below. 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. I checked the wall brackets and mast, but all the fixings were nice and tight. You can see the coil in the picture below (red arrow). Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. 1. The toroid with its many taps may be soldered directly on a multi-position switch. 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 . 100W on a Wire Antenna - How far would it reach? Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L.