Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. ON7EQ EFHW Antenna - qsl.net So I built myself an improved replacement matching transformer. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. I found it very useful to label the tuner with switch and capacitance positions. Look at the compensation coil slide. PDF shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m I use shock cord to connect the insulator at the end of the wire to my fence. clear. The antennas are set up as a sloper as in my SOTA outings. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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. Research salary, company info, career paths, and top skills for Software Engineer - EDI Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. 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. Understanding Antennas The Good, the Bad, and the Ugly. Many people use an inductor placed at the near end to make things level out on the higher bands. I will go back and have the article corrected. 2 0 obj Thanks in advance, good health for you in these times, Small efficient matching transformer for an EFHW - owenduffy.net Wrap the first wire around the toroid 27 times (I used a black wire for this). It uses a coil as a compensation unit, and no counterpoise. Your posting put it all together for meTHANK YOU!!!! Frank VK1VK. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. 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. <> 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. Next, I started winding the transformer. 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. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. 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. Be sure to take a look for additional analysis and conclusions. 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. I settled on a compact secondary using #28 wire. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. 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. How does this SWR meter works? Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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??). In an urban area we are much more restricted, especially if we need to be stealth about it. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. %PDF-1.4 . 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! Independent Medical Evaluation - IME | Cynthia Hennessey Highest frequency = 14.350 MHz. VSWR<1.8 over all of HF. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. 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. These dimensions were derived from modelling the antenna in EZNEC. I used the 14g enameled wire and wound it on the FT240-43. 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. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. ROB@COMCOIL.COM Instead, this shifts everything down and makes it very easy to tune 10m. 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. 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. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. 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. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. 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. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Taking the time derivative of the above equation you get the power dissipation. 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. Efhw Compensation Coil Experiment - Local Search Denver Post 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. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. 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. With no counterpoise wire it will be the coaxs shield providing it. The wire as I strung it up seemed to resist having a good SWR for the 20m band. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. The next important parameter is the parallel resonant circuits resonant frequency. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 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. That will be the missing resistor in the resistor bridge of the below circuit. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Current Balun 1. 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. It performed well on both the 2m and 70cm bands. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. = 258 * 10^-12. 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. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. This is perhaps one of the most hotly debated rookie topics in. It requires a set distance to hang both ends of the antenna, and that is not always given. 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. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. The radiation pattern of this antenna on most bands produces multiple lobes. Check your inbox or spam folder to confirm your subscription. At this point, I'm leaning towards the EFHW, but any of these antennas seem . Klubunknl folyamatos a tagfelvtel. Krem, rja le, mi a krdse. 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. Will there be the same performance for single band EFHWs? Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. How far could it possibly reach? The End-Fed Half Wave Antenna a bit Differently 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. This article will not address that antenna type. Also find news related to Efhw Compensation Coil Experiment which is trending today. There is lot of controversy around the EFHW antennas. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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. 5) It is very hard to avoid stray capacitance on the output. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. uBITX HF Transceiver Build - My Adventures in Engineering Not the ideal antenna, but convenient! I am building an EFHW antenna for my new. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The SWR results are as follows: The impedance per unit length of a lumped transmission line is where L and C are values per unit length. And not all hf antenna installation are same, with most requiring bit of tinkering. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. 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. Compensation. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. = .00 00 00 00 0 258 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. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. A radio station is as good or as bad as the antenna it has. Best regards and thanks again for your comment. So, how to construct an end-fed half wave antenna? 2015. Lowest frequency = 7.000 MHz. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. The tests here were using a dummy load on the transformer, and that did allow confirmation of the design and expected loss at 3.6MHz. 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. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. 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. 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. You cant really see the antenna wire, but the red line shows the antenna path. I look at the end-fed as just an extreme example of an off-center-fed antenna. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - DX Engineering All Rights Reserved. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Change), You are commenting using your Twitter account. 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. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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. Impressive article and so well done that I may give it a try. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. |k"^N>F.AnJkJsq'PV}o0I. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite It is all about getting the heat out. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Hence, we need to move along and start to include the antenna with our testing. Why does antenna radiation occur? Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Zin=46.52+j6.72. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Could it be something to do with the new vertical aerial I had recently installed? A method for estimating the impedance of a ferrite cored toroidal inductor at RF. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. There are many good descriptions on the net about this type of 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? Change), You are commenting using your Facebook account. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . 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. The difference here is that the target bands are low frequency. 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. There are two aspects, however that we need to consider: Lets begin with the transformer. In his article, I will try to bust some of the myths associated with Inverted. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. In theory, the examination is supposed to be used to help clarify your medical condition and . 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. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. 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 ran WSPR at 10mW for about 2 hours and got the results below. So the differences I see in the data sheets hysteresis curves are not the correct explanation. 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Is FT8 popularity growing at the cost of SSB Phone and CW? Be cautious, such voltages may cause a quite painful skin scorch. Experiments with 160m antennas | VK3IL Blog 2. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. 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. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. Then I covered the coil in kapton tape to hold it together. 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. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Hello, a wonderful approach for the problems.. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer 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. By using traps, the antenna works on all three bands with no operator interaction. From that we can find Mismatch Loss. As is often the case, packaging was determined by what boxes I had laying around. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. So far so good. For a quarter wave that is about 8 nS. Cmzett: Weince joseph How can we help? This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Apply for the Job in Software Engineer - EDI at St. Louis, MO. The technical storage or access that is used exclusively for anonymous statistical purposes. If you stare at the above frequency sweeps you will discover a few things. To further improve the flux linkage, I wound the primary on top of the secondary. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. Why had I not noticed this before? The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. The latest news about Efhw Compensation Coil Experiment. 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. 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. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. The Truth, ,and Nothing But The Truth (as I've experienced it) I decided to play with this to see what I could accomplish. This will yield the maximum capacity of the variable capacitor. Thanks for your comments. The negative effects of local QRM on an, How does antenna radiation occur? 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. Workers' Comp. First, note that the transformer has low transmission loss up to nearly 50MHz. What are its disadvantages? I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 73! The 2 coils are 35uh and 90uh. 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. 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. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. I tossed the line as far up as I could in a tree. It is recommended to use at least 2W non-inductive resistors for this purpose. Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. And now I am planning to build one for 160/80m. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. 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. Can a diode be used to rectify signals smaller than its threshold voltage? 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.) An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. It is not necessary to calculate the above; the results are sown in the following table. blue: 250pF, to much compensation. 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. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. This antenna is only 15m long using 2 loading coils. Trapped five band EFHW SOTA antenna. Isn't it? The toroid with its many taps may be soldered directly on a multi-position switch. It does not need any special components; in fact, most of us may have them in our shack drawers already. My design objectives were: 1. I mounted the transformer on a tree for testing. The technical storage or access that is used exclusively for statistical purposes. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside.