The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Jos van den Helm's (PA1ZP) article published in Radcom: 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. The original coil is designed for low power portable applications. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. The antenna is up. The EFHW transformer box from outside. The real power limit will be core heating. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. However, a key restriction is its 25W power rating, due to the small matching transformer. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. Looking at several builds and discussions, such as commercial antennas (e.g. Lets do a quick calculation to see how much an issue is this output capacitance. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. The cooling curve I measured is shown below. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. Could it be something to do with the new vertical aerial I had recently installed? If we wish to limit the ferrite temperature to 130 C, then assuming ambient temperature of 30 C, we can tolerate a 100 C temperature rise. |k"^N>F.AnJkJsq'PV}o0I. Apply for the Job in Software Engineer - EDI at St. Louis, MO. 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. End Fed Half Wave Antenna Coupler (EFHW) - M0UKD I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. Current Balun 1. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. I can give a link if you need. The final turns ratio turned out to be 3:29. The Counterpoise is a short, typically one twentieth (0.05 *. ) The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. To be safe, better not get much above 120 C. MyAntennas.com Group | When I'm measuring the half way point on my EFHW Above is a sweep of the roughly compensated transformer. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. How far could it possibly reach? My favorite SOTA antenna is the End-Fed Half Wave Antenna. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. Be cautious, such voltages may cause a quite painful skin scorch. Workers' Comp. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. Below about 7 MHz, transmission losses increase as the core temperature increases. 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. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. It is recommended to use at least 2W non-inductive resistors for this purpose. Thanks! This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. That will be the missing resistor in the resistor bridge of the below circuit. Looking at several builds and discussions, such as commercial antennas (e.g. IIRC they call it a "compensator". Above is a thermograph of the transformer at 20W input at 3.6MHz. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Im very pleased with that indeed. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. 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 . Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! 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). Thank you Gary. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. This can then, fed with coaxial cable, in many cases be . I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. 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. I would mention first its ease of installation. I assume you know the GNARC source for EFHW antennas. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. From that we can find Mismatch Loss. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. I found it very useful to label the tuner with switch and capacitance positions. 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. 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 that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. I tossed the line as far up as I could in a tree. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. One point of my small-core, compact winding design was to be able to cool the core. Your posting put it all together for meTHANK YOU!!!! The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. 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. 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 . Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. With such a switch, it is impossible to forget to switch back to operational mode. EFHW 80m extension - MI0KXX PDF shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m This is typically a weak spot. 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. 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. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. I checked the wall brackets and mast, but all the fixings were nice and tight. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. On the transformer, I added a few wingnuts to tighten down the antenna wire. 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. 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. To further improve the flux linkage, I wound the primary on top of the secondary. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. Not the ideal antenna, but convenient! However, it has its idiosyncrasies. Highest frequency = 14.350 MHz. 2015. 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. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. I am currently working on measurements of an EFHW antenna. 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). An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. clear. Z8Vq9_@x C\Agv#. Lowest frequency = 7.000 MHz. This antenna is working for 80,40,20,10 and 6m bands. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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). Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. Pocket-tenna core is finally done! Wire and compensation coil being My End-Fed Half-Wave (EFHW) AmateurRadio.com 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. 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? A short 80m antenna for my lot - KB6NU's Ham Radio Blog If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Above 7MHz, there is very little temperature dependence at all. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Basu Bhattacharya (VU2NSB). PDF MANUAL: ENDFEDZ 40-10-KW EFHW 1KW ICAS ANTENNA - Vibroplex The worse SWR was 1:1.7 at the top end of 20 meters. Just the bare 80m wire is shown in red. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. The band compensating inductor placed on the wire is another story. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. 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. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. : I see you were able to post your comment now, so I just copied my email answer here for others to see. coil inductance calculator at 66pacific.com. These dimensions were derived from modelling the antenna in EZNEC. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. This will yield the maximum capacity of the variable capacitor. 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. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. One end is about 5 meters high on an extended fishing pole. 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. I settled on a compact secondary using #28 wire. 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. Efhw Compensation Coil Experiment - Local Search Denver Post Csatlakozz csapatunkhoz! The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. This is not an optimal value, benefit may be obtained by exploring small changes to that value. We do not know what the actual impedance will be at the end of the antenna radiator. 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. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the 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. I mounted the transformer on a tree for testing. 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. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 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. You cant really see the antenna wire, but the red line shows the antenna path. 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. 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. I will go back and have the article corrected. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. 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. I particularly want to know how counterpoise affects the common mode currents on the coax. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Jim, do you mind if I add your email and my answer as a comment to the article? 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. 5) It is very hard to avoid stray capacitance on the output. Can you give me an idea for your 100 W version, you built for 80/60/40 m. Thanks again Jim. My question is what is 'higher frequency' specifically? Interpretation of S-Meter Noise Floor in HF Radio Receivers. A week or two later I started to notice an occasional knocking sound inside the house. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. If you stare at the above frequency sweeps you will discover a few things. Look at the compensation coil slide. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. So far so good. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite . <> The transformer fits sideways in the box with a few millimeters to spare. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. High self-resonant frequency. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. It is worth experimenting with its length also. 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. 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. Cmzett: Weince joseph How can we help? 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. Wrap the first wire around the toroid 27 times (I used a black wire for this). This suggests an inductive reactance. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. The parasitic reactances near the feed-point also vary between installations. Understanding Antennas The Good, the Bad, and the Ugly. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . Some say you do not need a counterpoise, but that is false. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? Instead, this shifts everything down and makes it very easy to tune 10m. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. Some website features may not function optimally without cookies. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). How does this SWR meter works? What are the advantages and disadvantages of the end-fed half wave antenna? 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. 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. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. By using traps, the antenna works on all three bands with no operator interaction. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. 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. 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. 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. uBITX HF Transceiver Build - My Adventures in Engineering Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. I chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. This will also be handling 100W. Hi Ajai, 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. % The following is the most up-to-date information related to EFHW Compensation Coil Experiment. Most of the time 5 to 20W will be adequate for activation anyway. They will be adjusted for resonance at or close to the CW portion of the bands. I am building an EFHW antenna for my new. It will present its parameters, so anybody with basic home-brew skills will be able to build it. Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. 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. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. 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