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. Although it is simple to build and is a multiband antenna, it has several attributes that . The computation method is also touched on. Subscribe to our newsletter and receive regular updates on new posts and articles. Thanks! The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. In the case of the EFHW 49:1 transformer, the major shortcomings of the most popular current designs are excessive leakage inductance and poor heat transfer from the ferrite material to the environment. 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). Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. This is typically a weak spot. 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. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . Current Balun 1. We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. I use shock cord to connect the insulator at the end of the wire to my fence. 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. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . 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 technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. For a quarter wave that is about 8 nS. A radio station is as good or as bad as the antenna it has. The EFHW transformer box from outside. What are its disadvantages? Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. And not all hf antenna installation are same, with most requiring bit of tinkering. 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%. The SWR for the 20 meter EFHW antenna was < 1.2:1 Frank VK1VK. 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. 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. 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. Let us touch on some necessary theory to begin with. More designs can be found by Googling "80m loaded dipole.". I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. The overlaid VSWR plots are shown below. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. The transformer fits sideways in the box with a few millimeters to spare. Just the bare 80m wire is shown in red. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. This will yield the maximum capacity of the variable capacitor. Wow, Gary! Thank you for your comment and feedback on the article about the EFHW antenna. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. The difference here is that the target bands are low frequency. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. Lowest frequency = 7.000 MHz. 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. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. 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. 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. Taking the time derivative of the above equation you get the power dissipation. Best regards and thanks again for your comment. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. How big and where to place it is likely best determined empirically. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Thank you for an interesting and informative read. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. 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. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. The next important parameter is the parallel resonant circuits resonant frequency. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. 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. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Zin=46.52+j6.72. Elnzst krnk, de elsikkadt az zenete. 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. Change). On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. The radiation pattern of this antenna on most bands produces multiple lobes. I installed a QRP SWR meter into the tuner that makes tuning very handy. However, a key restriction is its 25W power rating, due to the small matching transformer. Very interesting design. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Note: If we change the primary number of turns, the impedance ratios will considerable change also. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. And now I am planning to build one for 160/80m. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. 2015. This suggests an inductive reactance. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. Basically, the loading coil is operating as a trap. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). But systems that work better increase the prospects of contacts. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. 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. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. With no counterpoise wire it will be the coaxs shield providing it. I found it very useful to label the tuner with switch and capacitance positions. The antenna is effective and the materials and construction are of a very high quality. See the table above. The SWR results are as follows: Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. 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. 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. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. 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. This antenna is working for 80,40,20,10 and 6m bands. So, how to construct an end-fed half wave antenna? 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??). A 100pF silvered mica was connected in shunt with the transformer . Below about 7 MHz, transmission losses increase as the core temperature increases. It is not necessary to calculate the above; the results are sown in the following table. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. 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. Highest frequency = 14.350 MHz. 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. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. The antenna is effective and the materials and construction are of a very high quality. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? 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. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. P.S. Why does antenna radiation occur? After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. The final turns ratio turned out to be 3:29. 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 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. xZ
Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! 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. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Looking at several builds and discussions, such as commercial antennas (e.g. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. In his article, I will try to bust some of the myths associated with Inverted. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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 orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between 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. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Above, 3t on the primary delivers Gcore<0.002S. I added some Christmas colored zip ties to hold everything in place. But Ill find the error of my ways.and there are various on-line calculators to help me ensure I get the decimals and (H, mH, uH, pH, etc.) Then I covered the coil in kapton tape to hold it together. The impedance matching circuit is essentially a simple parallel resonant LC circuit. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. But I would caution its usage for higher power than 10-15W. So far so good. coil inductance calculator at 66pacific.com. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. Hence, there is no optimum single-fit solution. The real power limit will be core heating. 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. 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. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. However, it has its idiosyncrasies. Show more. 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