This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. However, it has its idiosyncrasies. 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. Let us touch on some necessary theory to begin with. Subscribe to our newsletter and receive regular updates on new posts and articles. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Could it be something to do with the new vertical aerial I had recently installed? 5) It is very hard to avoid stray capacitance on the output. ROB@COMCOIL.COM 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. I suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. Most informative and appreciated. The final turns ratio turned out to be 3:29. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. 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. Thank you for your comment and feedback on the article about the EFHW antenna. What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. Wrap the first wire around the toroid 27 times (I used a black wire for this). For the last step, I put together a RF choke to use between the radio and the feedline. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. Basu Bhattacharya (VU2NSB). This antenna is only 15m long using 2 loading coils. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. Simulating the end-fed half-wave (EFHW) dipole antenna To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. Many people use an inductor placed at the near end to make things level out on the higher bands. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. There is much more that can be written about this antenna and its matching, but that was not my aim. A 100pF silvered mica was connected in shunt with the transformer . Above 7MHz, there is very little temperature dependence at all. I checked the wall brackets and mast, but all the fixings were nice and tight. I am planning to use this latest one at the Field Day next year. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. No capacitor was installed. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Csatlakozz csapatunkhoz! The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. This suggests an inductive reactance. Be cautious, such voltages may cause a quite painful skin scorch. The negative effects of local QRM on an, How does antenna radiation occur? End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. For our transformer at 100W (==> 71 Vrms into 50 ) , the core cross section for the two FT114s is 0.74 cm2 , consider the lowest frequency as 3.5 MHz and our 5-turn primary, then plugging in the numbers we find Bmax = 0.012 T. Lets consider a much more challenging extreme: 1000W and the 160m band. To further improve the flux linkage, I wound the primary on top of the secondary. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. 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. Can I get away with no capacitor in my design? Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. So, how to construct an end-fed half wave antenna? A 100pF silvered mica was connected in shunt with the transformer primary. The combination of the transformer with the end-fed dipole results in a positive reactance. 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. Looking at several builds and discussions, such as commercial antennas (e.g. Hello, a wonderful approach for the problems.. 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 impedance per unit length of a lumped transmission line is where L and C are values per unit length. 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. Understanding Antennas The Good, the Bad, and the Ugly. I decided to push for best efficiency with a 5-turn primary. A short 80m antenna for my lot - KB6NU's Ham Radio Blog The equation in the article is corrected now. Is FT8 popularity growing at the cost of SSB Phone and CW? 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 technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 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. We use cookies to optimize our website and our service. It is better to build one for 160 and 80m, perhaps add 17m to the design described in this article, and for higher bands it is easier to use a linked dipole. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. ON7EQ EFHW Antenna - qsl.net Does your station desperately need a good RF ground to behave properly? I ran WSPR at 10mW for about 2 hours and got the results below. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. Low SSN Why do most Hams find HF Radio so difficult? Change), You are commenting using your Facebook account. One end is about 5 meters high on an extended fishing pole. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. In this case, it looks important. 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. . As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Consequently, this is how the capacitance values are determined. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. 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. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Show more. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. The computation method is also touched on. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. You cant really see the antenna wire, but the red line shows the antenna path. The original coil is designed for low power portable applications. 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. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. It is worth experimenting with its length also. 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. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. 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. Regards VE9HAM. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Thanks again Jim. These four data points are plotted on the Transmission Losses chart shown below as the yellow squares, all but the 80 meter point coming in a bit lower than expected losses based on the VNA measurements. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Above is a thermograph of the transformer at 20W input at 3.6MHz. We need to measure the inductances of the toroid with the tapped coil. A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. 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. 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. Nagyon j ez a cikk. 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 is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. The antenna is up. My design objectives were: 1. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Graphed with a log scale, it makes a nice straight line. High Q, hence low loss. The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex The End-Fed Half Wave Antenna a bit Differently The antenna is effective and the materials and construction are of a very high quality. Be sure to take a look for additional analysis and conclusions. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. As I reexamined my formula, you pointed it out correctly, there is an error in it. P.S. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. 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 started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 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. 2015. But I would caution its usage for higher power than 10-15W. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. The toroid with its many taps may be soldered directly on a multi-position switch. The model results show the need for a not entirely insignificant counterpoise. 2006. The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. It is not necessary to calculate the above; the results are sown in the following table. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. 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. If you really want to get the heat out, add some fins to the aluminum box. This will also be handling 100W. 100W on a Wire antenna! Proudly created withWix.com. 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. There are many good descriptions on the net about this type of antenna. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. End Fed Half Wave Antenna Coupler (EFHW) - M0UKD 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. To be safe, better not get much above 120 C. 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. 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. I then added two 220pf capacitors in series between the center conductor and ground. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. It should be no surprise that 80pF is close to optimal. 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. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! I first mounted the SO239 connector to the box. 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. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! The SWR figures were as follows: FT240-43 132ft/100pF capacitor It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Best regards and thanks again for your comment. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. EFHW 80m extension - MI0KXX Do I count the six loops around the pvc in the measurement? Ismerje meg a hozzszls adatainak feldolgozst . For . The cooling curve I measured is shown below. <> 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. This will yield the maximum capacity of the variable capacitor. This antenna is working for 80,40,20,10 and 6m bands. I checked the wall brackets and mast, but all the fixings were nice and tight. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. It is best to make the impedance matching adjustable, using switched transformation ratio. The band compensating inductor placed on the wire is another story. One way or another there is always a counterpoise involved if the antenna is tuned correctly. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Which begs the question what happens when you attach the antenna? The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. It is recommended to use at least 2W non-inductive resistors for this purpose. I dont have an amplifier, so only need to be able to handle 100W. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. uBITX HF Transceiver Build - My Adventures in Engineering These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. 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. 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? 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.

How To Remove Timestamp From Snapchat Memories, Shellpoint Mortgage Reo Department, 1987 High School Basketball Player Rankings, American Express Lounge Disney World, Phillipsburg Police Officer Kills Himself, Articles E