Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. The highest voltages as well as radiation are also at the end of the antenna wire. Above is a thermograph of the transformer at 20W input at 3.6MHz. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. 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. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 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. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. The band compensating inductor placed on the wire is another story. It is important that resonance may be achieved at each tap of the inductance. 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. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. of the wavelength. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. I checked the wall brackets and mast, but all the fixings were nice and tight. = .000001 / 3868.88 It will present its parameters, so anybody with basic home-brew skills will be able to build it. Could it be something to do with the new vertical aerial I had recently installed? It is not necessary to calculate the above; the results are sown in the following table. My question is what is 'higher frequency' specifically? Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. I needed to add an additional coil (approx 12.5 uH) about . The radiation pattern of this antenna on most bands produces multiple lobes. By using traps, the antenna works on all three bands with no operator interaction. 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. 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. It may be one or even five kilo-ohms. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. stream 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. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. There are two aspects, however that we need to consider: Lets begin with the transformer. Very interesting design. A ktelez mezket * karakterrel jelltk. 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. 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. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. 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. Below is the schematic of the final build. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. The total lenght is about 15mtr only and using 2 coils and a little stub (s) on the 80m coil or/and the 40m coil. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. 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. The cooling curve I measured is shown below. 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. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. : I see you were able to post your comment now, so I just copied my email answer here for others to see. 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. Im very pleased with that indeed. The results are shown below. One end is about 5 meters high on an extended fishing pole. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. P.S. VSWR<1.8 over all of HF. The wire as I strung it up seemed to resist having a good SWR for the 20m band. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Jim, do you mind if I add your email and my answer as a comment to the article? End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. 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. 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. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. I used four parallel #28 wires (not twisted) for the primary. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. I would mention first its ease of installation. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. Why had I not noticed this before? It is hard to wait an infinitely long time for the box to equilibrate to a given power level. That will be the missing resistor in the resistor bridge of the below circuit. 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. I can give a link if you need. I then used a piece of heat shrink on the outside to hold everything in place. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. I tossed the line as far up as I could in a tree. Copyright 2014-2023. The technical storage or access that is used exclusively for anonymous statistical purposes. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. I am planning to use this latest one at the Field Day next year. The transformer fits sideways in the box with a few millimeters to spare. 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 . Change), You are commenting using your Facebook account. We do not know what the actual impedance will be at the end of the antenna radiator. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. In theory, the examination is supposed to be used to help clarify your medical condition and . Trapped five band EFHW SOTA antenna. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. 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. All Rights Reserved. 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. The SWR for the 20 meter EFHW antenna was < 1.2:1 The results are presented below. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. We use cookies to optimize our website and our service. 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. To be safe, better not get much above 120 C. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. 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. With such a switch, it is impossible to forget to switch back to operational mode. 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. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. 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. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. I will go back and have the article corrected. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. And now I am planning to build one for 160/80m. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 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. i liked it a lot, you give good ideas, many thanks. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, Once I had upgraded the matching transformer for my EF-10/20/40 MKII "EndFedz" (see Part 1) my thoughts turned to the loading coil. 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??). 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. Thanks in advance, good health for you in these times, = 258 * 10^-12. 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. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. This antenna is only 15m long using 2 loading coils. I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. Be sure to take a look for additional analysis and conclusions. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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? I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. 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. 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). 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. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Basu Bhattacharya (VU2NSB). One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. A week or two later I started to notice an occasional knocking sound inside the house. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. 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! Thanks! 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 The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. Zin=46.52+j6.72. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. %PDF-1.4 Wrap the first wire around the toroid 27 times (I used a black wire for this). Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. Current Balun 1. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. 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 toroid with its many taps may be soldered directly on a multi-position switch. 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. 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. The EFHW transformer box from outside. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? 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. If not a lightning strike, I will write an article about the experience as well. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. How does this SWR meter works? 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. 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. They will be adjusted for resonance at or close to the CW portion of the bands. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. 100W on a Wire Antenna - Is it good enough for DX? If you stare at the above frequency sweeps you will discover a few things. My design objectives were: 1. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. For the last step, I put together a RF choke to use between the radio and the feedline. 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. So, how to construct an end-fed half wave antenna? It is all about getting the heat out. 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. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands.
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