'Capacitor flattens SWR at higher frequencies' - WA7ARK. The original coil is designed for low power portable applications. The overlaid VSWR plots are shown below. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. To be safe, better not get much above 120 C. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. 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%. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. application of Kirchhoff's current Law on a typical EFHW antenna configuration. They will be adjusted for resonance at or close to the CW portion of the bands. This article will not address that antenna type. 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. The model results show the need for a not entirely insignificant counterpoise. It is not necessary to calculate the above; the results are sown in the following table. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. Hence, there is no optimum single-fit solution. Low SSN Why do most Hams find HF Radio so difficult? = 258 * 10^-12. Could it be something to do with the new vertical aerial I had recently installed? Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. Check your inbox or spam folder to confirm your subscription. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 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. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. I am currently working on measurements of an EFHW antenna. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Next, I started winding the transformer. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. We need to measure the inductances of the toroid with the tapped coil. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The SWR for the 20 meter EFHW antenna was < 1.2:1 (LogOut/ Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. Although it is simple to build and is a multiband antenna, it has several attributes that . One point of my small-core, compact winding design was to be able to cool the core. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. 5) It is very hard to avoid stray capacitance on the output. Compensation. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. I needed to add an additional coil (approx 12.5 uH) about . Klubunknl folyamatos a tagfelvtel. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. 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. The final turns ratio turned out to be 3:29. 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? A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? This is not an optimal value, benefit may be obtained by exploring small changes to that value. How does this SWR meter works? This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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. I decided to push for best efficiency with a 5-turn primary. 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. Why had I not noticed this before? The equation should have a 10^6 and not 10^-6 in the nominator. blue: 250pF, to much compensation. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. coil inductance calculator at 66pacific.com. Why does antenna radiation occur? The patterns fro the horizontal wire is compared with those of an inverted-V configuration. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. 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. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? In an urban area we are much more restricted, especially if we need to be stealth about it. 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. Impressive article and so well done that I may give it a try. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Change), You are commenting using your Twitter account. 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. 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. Below is the schematic of the final build. 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. These dimensions were derived from modelling the antenna in EZNEC. 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. Regards VE9HAM. Above, 3t on the primary delivers Gcore<0.002S. It should be no surprise that 80pF is close to optimal. . The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. The toroid with its many taps may be soldered directly on a multi-position switch. 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. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Cmzett: Weince joseph How can we help? Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. It not a loading coil. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Elnzst krnk, de elsikkadt az zenete. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. 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. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. 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 .