The cooling curve I measured is shown below. 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. 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 transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. This will yield the maximum capacity of the variable capacitor. The SWR figures were as follows: FT240-43 132ft/100pF capacitor My design objectives were: 1. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. It performed well on both the 2m and 70cm bands. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. All Rights Reserved. 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. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. As you look to use this transformer at higher power levels, I can imagine that the bottleneck might be voltage breakdown or corona in the windings. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. On the transformer, I added a few wingnuts to tighten down the antenna wire. Wow, Gary! 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. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. 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. 100W on a Wire Antenna - How far would it reach? Hi Ajai, Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. I also will ask, why didnt it work for you. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. The negative effects of local QRM on an, How does antenna radiation occur? clear. 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. The bridge than will measure zero voltage across the bridge, and the LED will turn off. Finally the tank circuits specification is complete, which is sown below. 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. This is perhaps one of the most hotly debated rookie topics in. How to get started on ISS Cross band Repeater? 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. 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. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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). I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. Very interesting design. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! The results are presented below. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. Im very happy with the result. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. 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. 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. 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. 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. Which begs the question what happens when you attach the antenna? Some hams swear by them, yet some completely demean it. 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. Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). I can give a link if you need. 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 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. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. 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. 3) Total losses are approximately independent of core volume. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. With no counterpoise wire it will be the coaxs shield providing it. Change). For a quarter wave that is about 8 nS. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. 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. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Nagyon j ez a cikk. Wrap the first wire around the toroid 27 times (I used a black wire for this). This is not an optimal value, benefit may be obtained by exploring small changes to that value. Trapped five band EFHW SOTA antenna. 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. Compensation. VSWR<1.8 over all of HF. With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. 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. Many people use an inductor placed at the near end to make things level out on the higher bands. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! 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. Do I count the six loops around the pvc in the measurement? This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 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. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Thanks for your comments. The next important parameter is the parallel resonant circuits resonant frequency. More designs can be found by Googling "80m loaded dipole.". However, a key restriction is its 25W power rating, due to the small matching transformer. 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. 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. The equation in the article is corrected now. The results are shown below. blue: 250pF, to much compensation. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. What are its disadvantages? The difference here is that the target bands are low frequency. Workers' Comp. Krem, rja le, mi a krdse. Is it any good? 5) It is very hard to avoid stray capacitance on the output. 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). It is best to make the impedance matching adjustable, using switched transformation ratio. Show more. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. 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. 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. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. 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. 100W on a Wire antenna! 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. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. We use cookies to optimize our website and our service. And not all hf antenna installation are same, with most requiring bit of tinkering. Does your station desperately need a good RF ground to behave properly? 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. Refurbishing aluminium antenna parts affected by weather / corrosion. This article will not address that antenna type. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. See the second completed tuner depicted below. I decided to play with this to see what I could accomplish. I ran WSPR at 10mW for about 2 hours and got the results below. We do not know what the actual impedance will be at the end of the antenna radiator. We need to measure the inductances of the toroid with the tapped coil. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. I am currently working on measurements of an EFHW antenna. 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. 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. Current Balun 1. 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. 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. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? . Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. The Counterpoise is a short, typically one twentieth (0.05 *. ) The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. 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. Frank VK1VK. I then added two 220pf capacitors in series between the center conductor and ground. I am building an EFHW antenna for my new. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Hello, a wonderful approach for the problems.. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. 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. 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. P.S. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. 100W on a Wire Antenna How far would it reach?
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