The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. 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. I found it very useful to label the tuner with switch and capacitance positions. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 3) Total losses are approximately independent of core volume. For a quarter wave that is about 8 nS. 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. of the wavelength. The Counterpoise is a short, typically one twentieth (0.05 *. ) We do not know what the actual impedance will be at the end of the antenna radiator. The computation method is also touched on. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. = 1/30.e6 = 33 nS. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. Subscribe to our newsletter and receive regular updates on new posts and articles. Let me review the salient observations from the previous work. There is lot of controversy around the EFHW antennas. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. We use cookies to optimize our website and our service. Well, in ham radio, everything works. Z8Vq9_@x C\Agv#. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. It is all about getting the heat out. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. In an urban area we are much more restricted, especially if we need to be stealth about it. The negative effects of local QRM on an, How does antenna radiation occur? 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. 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. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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 . How badly can high Local Ambient QRM affect HF Radio? A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Elnzst krnk, de elsikkadt az zenete. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Even at 15W the voltage at the ends may reach 100-200V. Thanks in advance, good health for you in these times, It is not necessary to calculate the above; the results are sown in the following table. As is often the case, packaging was determined by what boxes I had laying around. This will yield the minimal capacitance of the variable capacitor. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. 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. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. 2006. I mounted the transformer on a tree for testing. The combination of the transformer with the end-fed dipole results in a positive reactance. Of course, you will need to find your tuning positions and apply your own position scale. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. It may be one or even five kilo-ohms. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Csatlakozz csapatunkhoz! 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.) Proudly created withWix.com. So far so good. 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 the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). How does this SWR meter works? 'Capacitor flattens SWR at higher frequencies' - WA7ARK. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The overall lenght is only 15m. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. 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. Your article was well written and very informative, thanks. (Tvir s tvbeszl gpek s kszlkek) Ksznm. We need to measure the inductances of the toroid with the tapped coil. 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. It uses a coil as a compensation unit, and no counterpoise. I used four parallel #28 wires (not twisted) for the primary. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. I used the 14g enameled wire and wound it on the FT240-43. 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. A radio station is as good or as bad as the antenna it has. And of course, a counterpoise with various lengths. Current Balun 1. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The wire as I strung it up seemed to resist having a good SWR for the 20m band. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. I then used a piece of heat shrink on the outside to hold everything in place. This will also be handling 100W. What are the advantages and disadvantages of the end-fed half wave antenna? 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. Apply for the Job in Software Engineer - EDI at St. Louis, MO. 2 0 obj A 100pF silvered mica was connected in shunt with the transformer primary. The biggest uncertainty in these measurements was the actual power level used. 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. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. Lowest frequency = 7.000 MHz. All Rights Reserved. I first mounted the SO239 connector to the box. It requires a set distance to hang both ends of the antenna, and that is not always given. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Do I count the six loops around the pvc in the measurement? 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. I decided to push for best efficiency with a 5-turn primary. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. Can a diode be used to rectify signals smaller than its threshold voltage? 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??). Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. 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. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. Some hams swear by them, yet some completely demean it. 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. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. Hence, there is no optimum single-fit solution. I will publish my findings, but I cannot not promise to complete it until early fall. That is an end-fed, but very different then the half wave construction. 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. 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. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). No wire counterpoise is used to reproduce the SOTA setup. Looking at several builds and discussions, such as commercial antennas (e.g. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. nanoVNA-H can firmware be updated if it has a broken USB socket? The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Why does a wire carrying RF current radiates to produce EM waves which travel through, Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. Most of the time 5 to 20W will be adequate for activation anyway. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. On the transformer, I added a few wingnuts to tighten down the antenna wire. The toroid with its many taps may be soldered directly on a multi-position switch. A ktelez mezket * karakterrel jelltk. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. See the second completed tuner depicted below. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. 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. 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! This antenna is working for 80,40,20,10 and 6m bands. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Very interesting design. Could it be something to do with the new vertical aerial I had recently installed? Not the ideal antenna, but convenient! It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Why had I not noticed this before? Select components with good insolating materials and properly chosen, relatively high voltage rated parts. This can then, fed with coaxial cable, in many cases be . is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 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. I decided to play with this to see what I could accomplish. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. 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. Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. Thank you for your comment and feedback on the article about the EFHW antenna. 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. Check your inbox or spam folder to confirm your subscription. 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'. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . I decided to play with this to see what I could accomplish. From that we can find Mismatch Loss. Low SSN Why do most Hams find HF Radio so difficult? The SWR for the 20 meter EFHW antenna was < 1.2:1 With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. Does your station desperately need a good RF ground to behave properly? I wish I had a simple answer, but really this is where some experimentation can pay off. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Looking at several builds and discussions, such as commercial antennas (e.g. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. 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. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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. 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. 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. 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. Make sure the first wire is wrapped evenly around the whole toroid. 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. I assume you know the GNARC source for EFHW antennas. It is not necessary to calculate the above; the results are sown in the following table. The EFHW transformer box from outside. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. Instead, this shifts everything down and makes it very easy to tune 10m. The real power limit will be core heating. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. A 100pF silvered mica was connected in shunt with the transformer . 100W on a Wire Antenna - Is it good enough for DX? 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. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. I checked the wall brackets and mast, but all the fixings were nice and tight. Although it is simple to build and is a multiband antenna, it has several attributes that . I am currently working on measurements of an EFHW antenna. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. You cant really see the antenna wire, but the red line shows the antenna path. 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. Start by wrapping the wire around the toroid. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. As I reexamined my formula, you pointed it out correctly, there is an error in it. 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. There is much more that can be written about this antenna and its matching, but that was not my aim. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. What kind of balun is this? 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. 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. Research salary, company info, career paths, and top skills for Software Engineer - EDI 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 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. Isn't it? Lets do a quick calculation to see how much an issue is this output capacitance. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. The equation in the article is corrected now. 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. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. 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. 100W on a Wire Antenna How far would it reach? Consider the RC time for a source with 2500 impedance into a 1pF capacitor. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. But systems that work better increase the prospects of contacts. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. It should be no surprise that 80pF is close to optimal. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? 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. 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. 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 last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. 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). 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. With such a switch, it is impossible to forget to switch back to operational mode. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. 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. The basic question before us is how does an antenna work? The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Thirty turns #28 are wound on the two FT114-43 cores. 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. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. 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. There are many good descriptions on the net about this type of antenna. : I see you were able to post your comment now, so I just copied my email answer here for others to see. 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). = .000001 / 3868.88 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. 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. A week or two later I started to notice an occasional knocking sound inside the house. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. Transmitting on 15 meters was impossible because of RF into the radio. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. % Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. The impedance matching circuit is essentially a simple parallel resonant LC circuit. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. With no counterpoise wire it will be the coaxs shield providing it. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. 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%. Taking the time derivative of the above equation you get the power dissipation. Zin=46.52+j6.72. I dont have an amplifier, so only need to be able to handle 100W.