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 In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Thanks! 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. 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. 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 antenna is working for 80,40,20,10 and 6m bands. Nagyon j ez a cikk. Isn't it? Change), You are commenting using your Facebook account. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. The SWR results are as follows: 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 coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. coil inductance calculator at 66pacific.com. Can I get away with no capacitor in my design? The antenna is up. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. The resistance (real) component of the impedance is right where we want it near 50 ohms. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. A week or two later I started to notice an occasional knocking sound inside the house. Hello, a wonderful approach for the problems.. Look at the compensation coil slide. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. 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. And not all hf antenna installation are same, with most requiring bit of tinkering. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 73 I look at the end-fed as just an extreme example of an off-center-fed antenna. . 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. I wish you lots of productive experimentations and successful portable operations. In this case, it looks important. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. xZ
Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! 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). 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). The biggest uncertainty in these measurements was the actual power level used. As is often the case, packaging was determined by what boxes I had laying around. Start by wrapping the wire around the toroid. Compensation. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. High self-resonant frequency. Is FT8 popularity growing at the cost of SSB Phone and CW? I decided to play with this to see what I could accomplish. I used the 14g enameled wire and wound it on the FT240-43. It may be one or even five kilo-ohms. The SWR figures were as follows: FT240-43 132ft/100pF capacitor The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Z8Vq9_@x C\Agv#. I can give a link if you need. 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. What kind of balun is this? I settled on a compact secondary using #28 wire. Hi Ajai, 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. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. Klubunknl folyamatos a tagfelvtel. The original coil is designed for low power portable applications. Show more. Krem, rja le, mi a krdse. 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. Two layers of 1mil Kapton tape are placed over the winding. 2015. 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. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. The SWR was measured for each of the three antennas across the CW portion of the bands. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Some website features may not function optimally without cookies. First, note that the transformer has low transmission loss up to nearly 50MHz. The final turns ratio turned out to be 3:29. To further improve the flux linkage, I wound the primary on top of the secondary. In his article, I will try to bust some of the myths associated with Inverted. The band compensating inductor placed on the wire is another story. A week or two later I started to notice an occasional knocking sound inside the house. Research salary, company info, career paths, and top skills for Software Engineer - EDI A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. Basu Bhattacharya (VU2NSB). The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. It is important that resonance may be achieved at each tap of the inductance. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. It is not necessary to calculate the above; the results are sown in the following table. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Can you give me an idea for your 100 W version, you built for 80/60/40 m. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. With no counterpoise wire it will be the coaxs shield providing it. 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. Thank you Gary. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. It performed well on both the 2m and 70cm bands. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. (LogOut/ I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. Above, 3t on the primary delivers Gcore<0.002S. 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. Very interesting design. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. The next important parameter is the parallel resonant circuits resonant frequency. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. 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. 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. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. 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. I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. The latest news about Efhw Compensation Coil Experiment. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. This will also be handling 100W. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. Which begs the question what happens when you attach the antenna? It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. Some hams swear by them, yet some completely demean it. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. The photos above show a method that works fairly well. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. However, a key restriction is its 25W power rating, due to the small matching transformer. As I reexamined my formula, you pointed it out correctly, there is an error in it. 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. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. 2. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. I decided to play with this to see what I could accomplish. We do not know what the actual impedance will be at the end of the antenna radiator. P.S. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. This is perhaps one of the most hotly debated rookie topics in. Lowest frequency = 7.000 MHz. My question is what is 'higher frequency' specifically? So, I embarked on testing it for myself. 2006. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. Frank VK1VK. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). These dimensions were derived from modelling the antenna in EZNEC. What are its disadvantages? The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. Not the ideal antenna, but convenient! But before we do, let us look at the insertion and transmission loss that the VNA is reporting. That will be the missing resistor in the resistor bridge of the below circuit. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. It is recommended to use at least 2W non-inductive resistors for this purpose. I first mounted the SO239 connector to the box. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. 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. After some internet research, I settled on making the former from a paint roller. Now I just need to build or acquire a decent radio to utilize this new antenna. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. 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. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. The combination of the transformer with the end-fed dipole results in a positive reactance. More designs can be found by Googling "80m loaded dipole.". Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Csatlakozz csapatunkhoz! Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. 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. I am currently working on measurements of an EFHW antenna. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 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.