A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. What are the advantages and disadvantages of the end-fed half wave antenna? 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. Which begs the question what happens when you attach the antenna? With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. 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. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. of the wavelength. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 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. There is lot of controversy around the EFHW antennas. Basu Bhattacharya (VU2NSB). Apply for the Job in Software Engineer - EDI at St. Louis, MO. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. Some website features may not function optimally without cookies. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. Above is a sweep of the uncompensated prototype with a 3220+50 load. . It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. 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. Is it any good? 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. It will present its parameters, so anybody with basic home-brew skills will be able to build it. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. Transmitting on 15 meters was impossible because of RF into the radio. blue: 250pF, to much compensation. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. ROB@COMCOIL.COM I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. A 100pF silvered mica was connected in shunt with the transformer primary. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. : I see you were able to post your comment now, so I just copied my email answer here for others to see. It is not necessary to calculate the above; the results are sown in the following table. It not a loading coil. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. More designs can be found by Googling "80m loaded dipole.". Be aware counterpoise or ground radials are required for all hf antennas for better performance. Most informative and appreciated. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. 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. It is worth experimenting with its length also. I checked the wall brackets and mast, but all the fixings were nice and tight. 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 . I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. 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. Change), You are commenting using your Twitter account. Note: If we change the primary number of turns, the impedance ratios will considerable change also. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. 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. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. The negative effects of local QRM on an, How does antenna radiation occur? Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). 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 mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. Also find news related to Efhw Compensation Coil Experiment which is trending today. The antennas are set up as a sloper as in my SOTA outings. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. The EFHW transformer box from outside. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. 100W on a Wire Antenna - How far would it reach? Most of the time 5 to 20W will be adequate for activation anyway. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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. Below about 7 MHz, transmission losses increase as the core temperature increases. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. 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. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. 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. . In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. So I built myself an improved replacement matching transformer. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. 3) Total losses are approximately independent of core volume. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Highest frequency = 14.350 MHz. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Why had I not noticed this before? 100W on a Wire antenna! Above, 3t on the primary delivers Gcore<0.002S. 2006. So, how to construct an end-fed half wave antenna? There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. Let us touch on some necessary theory to begin with. Refurbishing aluminium antenna parts affected by weather / corrosion. The bridge than will measure zero voltage across the bridge, and the LED will turn off. That is an end-fed, but very different then the half wave construction. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. Wow, Gary! One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. They will be adjusted for resonance at or close to the CW portion of the 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, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. I can give a link if you need. It is not necessary to calculate the above; the results are sown in the following table. 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. The technical storage or access that is used exclusively for anonymous statistical purposes. (LogOut/ The Counterpoise is a short, typically one twentieth (0.05 *. ) What are its disadvantages? From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Csatlakozz csapatunkhoz! Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Understanding Antennas The Good, the Bad, and the Ugly. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. Start by wrapping the wire around the toroid. 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. I tossed the line as far up as I could in a tree. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. 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. The parasitic reactances near the feed-point also vary between installations. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. 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. 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. 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. Check your inbox or spam folder to confirm your subscription. 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. 100W on a Wire Antenna How far would it reach? Not the ideal antenna, but convenient! Can I get away with no capacitor in my design? 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. One way or another there is always a counterpoise involved if the antenna is tuned correctly. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. 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.
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