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. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. There is lot of controversy around the EFHW antennas. 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. The overlaid VSWR plots are shown below. The antenna is effective and the materials and construction are of a very high quality. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. 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. 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. The original coil is designed for low power portable applications. Many people use an inductor placed at the near end to make things level out on the higher bands. This gave me an effective coil diameter of 40.5mm. It requires a set distance to hang both ends of the antenna, and that is not always given. 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. 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. 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 wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. It performed well on both the 2m and 70cm bands. One end is about 5 meters high on an extended fishing pole. The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. end fed half wave antenna - awsh.org From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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 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. Although it is simple to build and is a multiband antenna, it has several attributes that . 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. The next important parameter is the parallel resonant circuits resonant frequency. So, how to construct an end-fed half wave antenna? First, note that the transformer has low transmission loss up to nearly 50MHz. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. The aluminum box is the logical heatsink, so I cut a few scraps of aluminum to make a thermal connection to the bottom of the box and to the lid, adjusting with aluminum shims so that when the box lid is screw down, the entire thermal assembly, with the cores in the middle, is under a little compression. The technical storage or access that is used exclusively for anonymous statistical purposes. Of course, if both ends are raised higher, it will produce a more efficiently radiating antenna, but the portable and temporary installation is always compromised by conditions given by a location and its restrictions. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. With no counterpoise wire it will be the coaxs shield providing it. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. At this point, I'm leaning towards the EFHW, but any of these antennas seem . It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Interpretation of S-Meter Noise Floor in HF Radio Receivers. The transformer fits sideways in the box with a few millimeters to spare. = 1/30.e6 = 33 nS. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite 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. How to get started on ISS Cross band Repeater? And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near 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. You can see the coil in the picture below (red arrow). 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. Even at 15W the voltage at the ends may reach 100-200V. 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 will publish my findings, but I cannot not promise to complete it until early fall. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. Above is a sweep of the roughly compensated transformer. Of course, you will need to find your tuning positions and apply your own position scale. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. Trapped five band EFHW SOTA antenna. This is typically a weak spot. The equation in the article is corrected now. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. Thanks! End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio 100W on a Wire Antenna How far would it reach? Below is the schematic of the final build. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. A short 80m antenna for my lot - KB6NU's Ham Radio Blog It will present its parameters, so anybody with basic home-brew skills will be able to build it. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. I am building an EFHW antenna for my new. These dimensions were derived from modelling the antenna in EZNEC. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! Isn't it? To be safe, better not get much above 120 C. EFHW Antenna Frequency Compensation Lead - YouTube Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. The model results show the need for a not entirely insignificant counterpoise. 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. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. I settled on a compact secondary using #28 wire. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. MyAntennas.com Group | When I'm measuring the half way point on my EFHW I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? 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. 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. (Tvir s tvbeszl gpek s kszlkek) Ksznm. The latest news about Efhw Compensation Coil Experiment. For a quarter wave that is about 8 nS. The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). 73! It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. The 2 coils are 35uh and 90uh. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. Let's find out! 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. It does not need any special components; in fact, most of us may have them in our shack drawers already. 100W on a Wire Antenna - How far would it reach? Krem, rja le, mi a krdse. Be sure to take a look for additional analysis and conclusions. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. 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. Above 7MHz, there is very little temperature dependence at all. So, I embarked on testing it for myself. The antenna is up. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. 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. I dont have an amplifier, so only need to be able to handle 100W. So I built myself an improved replacement matching transformer. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. The impedance matching circuit is essentially a simple parallel resonant LC circuit. VK1OD.net (offline). The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . 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 solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. 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. 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. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Will there be the same performance for single band EFHWs? I used the 14g enameled wire and wound it on the FT240-43. What kind of balun is this? Select components with good insolating materials and properly chosen, relatively high voltage rated parts. 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. . However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. More designs can be found by Googling "80m loaded dipole.". 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. Frank VK1VK. Why does a wire carrying RF current radiates to produce EM waves which travel through, Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. Highest frequency = 14.350 MHz. 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. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC Finally the tank circuits specification is complete, which is sown below. 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. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. A 100pF silvered mica was connected in shunt with the transformer . End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. 2015. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. 73 Instead, this shifts everything down and makes it very easy to tune 10m. Why had I not noticed this before? Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. This antenna is only 15m long using 2 loading coils. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Basu Bhattacharya (VU2NSB). From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The SWR for the 20 meter EFHW antenna was < 1.2:1 Can a diode be used to rectify signals smaller than its threshold voltage? It is not necessary to calculate the above; the results are sown in the following table. Now I just need to build or acquire a decent radio to utilize this new antenna. Hence, there is no optimum single-fit solution. Change), You are commenting using your Twitter account. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Thank you for your comment and feedback on the article about the EFHW antenna. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com There is much more that can be written about this antenna and its matching, but that was not my aim. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. The antenna is effective and the materials and construction are of a very high quality. The resistance (real) component of the impedance is right where we want it near 50 ohms. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. 2 0 obj 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. No capacitor was installed. 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. From that we can find Mismatch Loss. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Note: If we change the primary number of turns, the impedance ratios will considerable change also. I would mention first its ease of installation. I added some Christmas colored zip ties to hold everything in place. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. It uses a coil as a compensation unit, and no counterpoise. The technical storage or access that is used exclusively for statistical purposes. 3) Total losses are approximately independent of core volume. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. In his article, I will try to bust some of the myths associated with Inverted. 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. As I reexamined my formula, you pointed it out correctly, there is an error in it. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. Well, in ham radio, everything works. The previous table already contains these measurements. 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. The highest frequency could be14.350MHz. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. Can you give me an idea for your 100 W version, you built for 80/60/40 m. This reveals we only need to compensate for the reactive component. We use cookies to optimize our website and our service. stream Not the ideal antenna, but convenient! 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. The band compensating inductor placed on the wire is another story. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. 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. 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'. It is best to make the impedance matching adjustable, using switched transformation ratio. I first mounted the SO239 connector to the box. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. This will also be handling 100W. Regards VE9HAM. 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