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Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. 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. 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. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Make sure the first wire is wrapped evenly around the whole toroid. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Thanks for your comments. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). Firstly, bandwidth on 80m is restricted to about 80 kHz at . VK1OD.net (offline). The SWR figures were as follows: FT240-43 132ft/100pF capacitor 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. 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. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Thanks in advance, good health for you in these times, There is much more that can be written about this antenna and its matching, but that was not my aim. 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. 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. More designs can be found by Googling "80m loaded dipole.". Let's find out! 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. As I reexamined my formula, you pointed it out correctly, there is an error in it. 3) Total losses are approximately independent of core volume. Highest frequency = 14.350 MHz. 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. It may be one or even five kilo-ohms. The antenna is effective and the materials and construction are of a very high quality. 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. Apply for the Job in Software Engineer - EDI at St. Louis, MO. There are many good descriptions on the net about this type of antenna. stream The highest frequency could be14.350MHz. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. clear. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. I wish you lots of productive experimentations and successful portable operations. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. 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. However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings. Trapped five band EFHW SOTA antenna. 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. 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. Cmzett: Weince joseph How can we help? This can then, fed with coaxial cable, in many cases be . Lets call this element the LoadAttenuator. 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. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. Some hams swear by them, yet some completely demean it. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. A 100pF silvered mica was connected in shunt with the transformer . If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. It is all about getting the heat out. Graphed with a log scale, it makes a nice straight line. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Then I covered the coil in kapton tape to hold it together. The computation method is also touched on. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. We use cookies to optimize our website and our service. I tossed the line as far up as I could in a tree. 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. <> A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. But I would caution its usage for higher power than 10-15W. A 100pF silvered mica was connected in shunt with the transformer primary. However, a key restriction is its 25W power rating, due to the small matching transformer. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. 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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 am planning to use this latest one at the Field Day next year. It requires a set distance to hang both ends of the antenna, and that is not always given. 100W on a Wire Antenna How far would it reach? Jim, do you mind if I add your email and my answer as a comment to the article? 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. With such a switch, it is impossible to forget to switch back to operational mode. Zin=46.52+j6.72. I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. I used four parallel #28 wires (not twisted) for the primary. Frank VK1VK. 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. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. Above is a sweep of the roughly compensated transformer. The results are presented below. 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. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. 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. Copyright 2014-2023. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. If you stare at the above frequency sweeps you will discover a few things. Let me review the salient observations from the previous work. See the table above. 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. The antenna is effective and the materials and construction are of a very high quality. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Start by wrapping the wire around the toroid. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Show more. One point of my small-core, compact winding design was to be able to cool the core. 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. The biggest uncertainty in these measurements was the actual power level used. Two layers of 1mil Kapton tape are placed over the winding. Above, 3t on the primary delivers Gcore<0.002S. Your posting put it all together for meTHANK YOU!!!! It is worth experimenting with its length also. Thank you Gary. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. I decided to play with this to see what I could accomplish. You can start with the links below. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. 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. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. 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 .