efhw compensation coil efhw compensation coil

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. 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. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. It is very hard to know what will be the best solution for a given antenna installation if you want to hit all of the bands exactly. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. How far could it possibly reach? The 2 coils are 35uh and 90uh. There is much more that can be written about this antenna and its matching, but that was not my aim. Thank you for an interesting and informative read. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. This suggests an inductive reactance. So, how to construct an end-fed half wave antenna? And not all hf antenna installation are same, with most requiring bit of tinkering. Lowest measured inductivity = 2.0 H. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. It is recommended to use at least 2W non-inductive resistors for this purpose. 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. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. Lets do a quick calculation to see how much an issue is this output capacitance. For a quarter wave that is about 8 nS. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. The real power limit will be core heating. Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Cmzett: Weince joseph How can we help? You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 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. I mounted the transformer on a tree for testing. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Of course, you will need to find your tuning positions and apply your own position scale. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. All Rights Reserved. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. I wish I had a simple answer, but really this is where some experimentation can pay off. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. High self-resonant frequency. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. This article will not address that antenna type. The equation should have a 10^6 and not 10^-6 in the nominator. I will go back and have the article corrected. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. After some internet research, I settled on making the former from a paint roller. 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. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. clear. 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. Change), You are commenting using your Twitter account. Interpretation of S-Meter Noise Floor in HF Radio Receivers. The SWR was measured for each of the three antennas across the CW portion of the bands. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. No wire counterpoise is used to reproduce the SOTA setup. I added some Christmas colored zip ties to hold everything in place. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . 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. = .00 00 00 00 0 258 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). 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. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. The SWR for the 20 meter EFHW antenna was < 1.2:1 Thank you Gary. 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. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The overlaid VSWR plots are shown below. Then I covered the coil in kapton tape to hold it together. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. 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. 5) It is very hard to avoid stray capacitance on the output. I look at the end-fed as just an extreme example of an off-center-fed antenna. Thank you for your comment and feedback on the article about the EFHW antenna. Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. If not a lightning strike, I will write an article about the experience as well. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. 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. 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. Workers' Comp. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? (LogOut/ The original coil is designed for low power portable applications. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Can I get away with no capacitor in my design? Thirty turns #28 are wound on the two FT114-43 cores. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. To be safe, better not get much above 120 C. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. 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. The Counterpoise is a short, typically one twentieth (0.05 *. ) The technical storage or access that is used exclusively for anonymous statistical purposes. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Thanks in advance, good health for you in these times, ROB@COMCOIL.COM With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. The EFHW transformer box from outside. I decided to push for best efficiency with a 5-turn primary. Start by wrapping the wire around the toroid. In theory, the examination is supposed to be used to help clarify your medical condition and . . However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Below about 7 MHz, transmission losses increase as the core temperature increases. Regards VE9HAM. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 73 Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. I use shock cord to connect the insulator at the end of the wire to my fence. The combination of the transformer with the end-fed dipole results in a positive reactance. Next, I started winding the transformer. Why had I not noticed this before? 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. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. 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. That is an end-fed, but very different then the half wave construction. (Tvir s tvbeszl gpek s kszlkek) Ksznm. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. 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 . Note: If we change the primary number of turns, the impedance ratios will considerable change also. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. 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. The resistance (real) component of the impedance is right where we want it near 50 ohms. 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. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. 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??). 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. 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. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Can a diode be used to rectify signals smaller than its threshold voltage? The technical storage or access that is used exclusively for statistical purposes. 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. Two layers of 1mil Kapton tape are placed over the winding. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. 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 chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. 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. 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 designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Csatlakozz csapatunkhoz! I decided to play with this to see what I could accomplish. My design objectives were: 1. 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. You cant really see the antenna wire, but the red line shows the antenna path. 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). 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. Some say you do not need a counterpoise, but that is false. It is important that resonance may be achieved at each tap of the inductance. Krem, rja le, mi a krdse. I first mounted the SO239 connector to the box. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. The basic question before us is how does an antenna work? 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . 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 found that sometimes the multimeter that was measuring the temperature would give unreliable information when RF was present, so the off periods provided regular intervals for measuring the temperature.