My question is what is 'higher frequency' specifically? 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. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. Hence, there is no optimum single-fit solution. = 1/30.e6 = 33 nS. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. A 100pF silvered mica was connected in shunt with the transformer primary. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? . 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 in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Proudly created withWix.com. Wow, Gary! Let me review the salient observations from the previous work. 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 then used a piece of heat shrink on the outside to hold everything in place. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. I came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. From that we can find Mismatch Loss. No wire counterpoise is used to reproduce the SOTA setup. Yes, indeed EFHW antennas are very useful for SOTA or other field 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. 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. The SWR was measured for each of the three antennas across the CW portion of the bands. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. 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. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. . xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! P.S. The antenna is up. Thanks! Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. Research salary, company info, career paths, and top skills for Software Engineer - EDI Just the bare 80m wire is shown in red. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. The antenna is effective and the materials and construction are of a very high quality. If not a lightning strike, I will write an article about the experience as well. I was curious why this capacitor was added to the transformer. See the table above. It is not necessary to calculate the above; the results are sown in the following table. 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. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. 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 also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. Is FT8 popularity growing at the cost of SSB Phone and CW? Could it be something to do with the new vertical aerial I had recently installed? The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. 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. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. Very interesting design. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. There is much more that can be written about this antenna and its matching, but that was not my aim. 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. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Let us touch on some necessary theory to begin with. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. I decided to push for best efficiency with a 5-turn primary. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. Do I count the six loops around the pvc in the measurement? An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Start by wrapping the wire around the toroid. The technical storage or access that is used exclusively for statistical purposes. Best regards and thanks again for your comment. The band compensating inductor placed on the wire is another story. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Change), You are commenting using your Facebook account. 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. High self-resonant frequency. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. 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. Be sure to take a look for additional analysis and conclusions. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. I also will ask, why didnt it work for you. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. The worse SWR was 1:1.7 at the top end of 20 meters. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR. 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. The transformer fits sideways in the box with a few millimeters to spare. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. 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. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. 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. 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. Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. And now I am planning to build one for 160/80m. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. 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Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. 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. 2006. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. This can then, fed with coaxial cable, in many cases be . What are its disadvantages? With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. 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 used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. 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. 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. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Jim, do you mind if I add your email and my answer as a comment to the article? This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. This provides proper insulation from the relatively high voltages on the seconder winding. 2. I found it very useful to label the tuner with switch and capacitance positions. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. It does not need any special components; in fact, most of us may have them in our shack drawers already. Finally the tank circuits specification is complete, which is sown below. 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. 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%. 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. The results are presented below. 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. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. After some internet research, I settled on making the former from a paint roller. I am currently working on measurements of an EFHW antenna. Jos van den Helm's (PA1ZP) article published in Radcom: Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. Make sure the first wire is wrapped evenly around the whole toroid. Which begs the question what happens when you attach the antenna? 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. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Why had I not noticed this before? PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. No capacitor was installed. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. This is perhaps one of the most hotly debated rookie topics in. So the differences I see in the data sheets hysteresis curves are not the correct explanation. 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. Consequently, this is how the capacitance values are determined. 2 0 obj 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. Many people use an inductor placed at the near end to make things level out on the higher bands. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. If you really want to get the heat out, add some fins to the aluminum box. Interpretation of S-Meter Noise Floor in HF Radio Receivers. I ran WSPR at 10mW for about 2 hours and got the results below. I wish you lots of productive experimentations and successful portable operations. Isn't it? 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. 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. (LogOut/ This suggests an inductive reactance. The SWR figures were as follows: FT240-43 132ft/100pF capacitor These dimensions were derived from modelling the antenna in EZNEC. 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. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. 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. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. This antenna is only 15m long using 2 loading coils. The equation in the article is corrected now. 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 should be no surprise that 80pF is close to optimal. = .00 00 00 00 0 258 My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. It performed well on both the 2m and 70cm bands. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. I added some Christmas colored zip ties to hold everything in place. For the last step, I put together a RF choke to use between the radio and the feedline. 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. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). 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. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. In this case, it looks important. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. 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. (LogOut/ 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. 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. A radio station is as good or as bad as the antenna it has. The negative effects of local QRM on an, How does antenna radiation occur? It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. 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. 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. 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. = .000001 / 3868.88 A method for estimating the impedance of a ferrite cored toroidal inductor at RF. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Below is the schematic of the final build. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). In comparison to the EFHW antenna, a simple dipole offers a far better prospect. There are two aspects, however that we need to consider: Lets begin with the transformer. 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. I will publish my findings, but I cannot not promise to complete it until early fall. One point of my small-core, compact winding design was to be able to cool the core. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. Highest frequency = 14.350 MHz. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The highest voltages as well as radiation are also at the end of the antenna wire. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. That is an end-fed, but very different then the half wave construction. I mounted the transformer on a tree for testing. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. 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. %PDF-1.4 But before we do, let us look at the insertion and transmission loss that the VNA is reporting. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Looking at several builds and discussions, such as commercial antennas (e.g. Some hams swear by them, yet some completely demean it. Basu Bhattacharya (VU2NSB). 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. The goal of the temperature characterization is to determine how much temperature difference (core to ambient) there will be for a given level of power dissipation. The highest frequency could be14.350MHz. Graphed with a log scale, it makes a nice straight line. It is not necessary to calculate the above; the results are sown in the following table. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. 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. 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. Can I get away with no capacitor in my design? This article will not address that antenna type. I checked the wall brackets and mast, but all the fixings were nice and tight. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency.

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