How far could it possibly reach? 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. Im very happy with the result. The EFHW transformer box from outside. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 73 And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? Current Balun 1. 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. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. The results are shown below.
End Fed Half Wave Antenna Coupler (EFHW) - M0UKD How to get started on ISS Cross band Repeater? I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. The Counterpoise is a short, typically one twentieth (0.05 *. ) This will yield the maximum capacity of the variable capacitor.
The 40-10m EFHW camping antenna is late but done. More info in - reddit I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. The 2 coils are 35uh and 90uh. It requires a set distance to hang both ends of the antenna, and that is not always given. Hi Ajai, This graphical depiction makes it easier to visualize the current and impedance correlation between bands. 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. 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 antenna is effective and the materials and construction are of a very high quality.
Experiments with 160m antennas | VK3IL Blog 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. 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. The antenna is up. The photos above show a method that works fairly well. Although the original loading coil is very well engineered, I thought I could make a more efficient version given that I did not need to make it 'trail friendly'. The toroid with its many taps may be soldered directly on a multi-position switch. 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. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. 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. The worse SWR was 1:1.7 at the top end of 20 meters. Let me review the salient observations from the previous work.
It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. 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. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. I used the 14g enameled wire and wound it on the FT240-43.
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). 2015. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. %PDF-1.4 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. 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. To be safe, better not get much above 120 C.
A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. 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. Isn't it? This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. Ismerje meg a hozzszls adatainak feldolgozst . Graphed with a log scale, it makes a nice straight line. 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. It is not necessary to calculate the above; the results are sown in the following table. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. 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. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. High self-resonant frequency. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Could it be something to do with the new vertical aerial I had recently installed? Wow, Gary! But I would caution its usage for higher power than 10-15W. One end is about 5 meters high on an extended fishing pole. However, it has its idiosyncrasies. I added some Christmas colored zip ties to hold everything in place. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. 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. 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. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. 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. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. This antenna is only 15m long using 2 loading coils.
Efhw Compensation Coil Experiment - Local Search Denver Post 100W on a Wire antenna! Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. Not the ideal antenna, but convenient! Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. How does this SWR meter works? One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. (LogOut/ Thank you for an interesting and informative read. The original coil is designed for low power portable applications. Zin=46.52+j6.72. The highest frequency could be14.350MHz. Nagyon j ez a cikk. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. 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.
MyAntennas.com Group | When I'm measuring the half way point on my EFHW 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. 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. Change), You are commenting using your Facebook account. They will be adjusted for resonance at or close to the CW portion of the bands. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. A week or two later I started to notice an occasional knocking sound inside the house. 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.
My End-Fed Half-Wave (EFHW) AmateurRadio.com Lets do a quick calculation to see how much an issue is this output capacitance. The biggest uncertainty in these measurements was the actual power level used. 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. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. Very interesting design. I would mention first its ease of installation.
End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? I mounted the transformer on a tree for testing. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. 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. Check your inbox or spam folder to confirm your subscription. 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.
Energy Assistance (LIHEAP) | Crosswalk Community Action Agency Above 7MHz, there is very little temperature dependence at all. 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. The negative effects of local QRM on an, How does antenna radiation occur? During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. Why does antenna radiation occur? 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.
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. Workers' Comp. clear. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio.
EFHW Compensation Coil Experiment - YouTube Some website features may not function optimally without cookies. The SWR results are as follows:
EFHW 80m extension - MI0KXX I ran WSPR at 10mW for about 2 hours and got the results below. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. xZ
Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! Interpretation of S-Meter Noise Floor in HF Radio Receivers. This antenna is working for 80,40,20,10 and 6m bands. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. The SWR for the 20 meter EFHW antenna was < 1.2:1