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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 . 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. 100W on a Wire Antenna How far would it reach? This is typically a weak spot. 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. 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. 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. Refurbishing aluminium antenna parts affected by weather / corrosion. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. 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 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 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. % Not the ideal antenna, but convenient! 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. Current Balun 1. Many people use an inductor placed at the near end to make things level out on the higher bands. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. A 100pF silvered mica was connected in shunt with the transformer . Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. The cooling curve I measured is shown below. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. Let us touch on some necessary theory to begin with. Of course, you will need to find your tuning positions and apply your own position scale. The technical storage or access that is used exclusively for anonymous statistical purposes. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. This article will not address that antenna type. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. You can start with the links below. 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. The worse SWR was 1:1.7 at the top end of 20 meters. Above is a sweep of the uncompensated prototype with a 3220+50 load. View the job description, responsibilities and qualifications for this position. It is best to make the impedance matching adjustable, using switched transformation ratio. I am currently working on measurements of an EFHW antenna. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. 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. How far could it possibly reach? After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. One point of my small-core, compact winding design was to be able to cool the core. 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. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. 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. The results are shown below. Zin=46.52+j6.72. 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. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. This provides proper insulation from the relatively high voltages on the seconder winding. The SWR for the 20 meter EFHW antenna was < 1.2:1 Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. Copyright 2014-2023. 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). 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. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. It may be one or even five kilo-ohms. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! 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. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. 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. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. I wish I had a simple answer, but really this is where some experimentation can pay off. 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. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. The original coil is designed for low power portable applications. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. 2 0 obj End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. 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. Change), You are commenting using your Twitter account. The difference here is that the target bands are low frequency. Then I covered the coil in kapton tape to hold it together. You can see the coil in the picture below (red arrow). 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). It performed well on both the 2m and 70cm bands. 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. 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. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. 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 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. I first mounted the SO239 connector to the box. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. And now I am planning to build one for 160/80m. 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. Lowest frequency = 7.000 MHz. Hello, a wonderful approach for the problems.. I mounted the transformer on a tree for testing. 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. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength.