efhw compensation coil

The impedance per unit length of a lumped transmission line is where L and C are values per unit length. 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. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. For . 73! It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 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. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. The final turns ratio turned out to be 3:29. The original coil is designed for low power portable applications. 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. It will present its parameters, so anybody with basic home-brew skills will be able to build it. 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. View the job description, responsibilities and qualifications for this position. 100W on a Wire Antenna How far would it reach? This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Lets do a quick calculation to see how much an issue is this output capacitance. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. They will be adjusted for resonance at or close to the CW portion of the bands. The negative effects of local QRM on an, How does antenna radiation occur? Some hams swear by them, yet some completely demean it. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. 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. Zin=46.52+j6.72. Could it be something to do with the new vertical aerial I had recently installed? Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. 100W on a Wire Antenna - Is it good enough for DX? High Q, hence low loss. = .00 00 00 00 0 258 The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. My question is what is 'higher frequency' specifically? The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. It should be no surprise that 80pF is close to optimal. The radiation pattern of this antenna on most bands produces multiple lobes. What are its disadvantages? I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. You can see the coil in the picture below (red arrow). 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. I assume you know the GNARC source for EFHW antennas. A radio station is as good or as bad as the antenna it has. Next, I started winding the transformer. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, Once I had upgraded the matching transformer for my EF-10/20/40 MKII "EndFedz" (see Part 1) my thoughts turned to the loading coil. Some say you do not need a counterpoise, but that is false. stream 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. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! I then used a piece of heat shrink on the outside to hold everything in place. Hence, there is no optimum single-fit solution. 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. Thanks! This will yield the maximum capacity of the variable capacitor. 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. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. i liked it a lot, you give good ideas, many thanks. 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. I settled on a compact secondary using #28 wire. This provides proper insulation from the relatively high voltages on the seconder winding. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. 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. With no counterpoise wire it will be the coaxs shield providing it. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 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. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. I used the 14g enameled wire and wound it on the FT240-43. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. 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. 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. 100W on a Wire antenna! Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave 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? I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. 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. 2006. Graphed with a log scale, it makes a nice straight line. Then I covered the coil in kapton tape to hold it together. The original coil is designed for low power portable applications. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. 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. 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. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. = .000001 / 3868.88 A ktelez mezket * karakterrel jelltk. The highest frequency could be14.350MHz. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. From that we can find Mismatch Loss. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. 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. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF It is all about getting the heat out. 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. 2 0 obj Be cautious, such voltages may cause a quite painful skin scorch. One possible explanation is that the core losses drop with temperature. 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. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. Start by wrapping the wire around the toroid. It does not need any special components; in fact, most of us may have them in our shack drawers already. Most informative and appreciated. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. You can start with the links below. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. 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. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. Above is a thermograph of the transformer at 20W input at 3.6MHz. How far could it possibly reach? I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. 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. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). I am planning to use this latest one at the Field Day next year. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. This will yield the minimal capacitance of the variable capacitor. 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. I found it very useful to label the tuner with switch and capacitance positions. 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. Just the bare 80m wire is shown in red. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" Pacific Ridge School Teacher Salary, Grandson Killed Grandfather, Articles E