Re: Topband: Verticals on the beach
Stan Stockton wrote: >>> Specifically what I want to find out is how much louder I would likely be >>> in Europe from 25 degrees to 50 degrees if the vertical was on that line >>> you drew as compared to being 70 feet below the line. >>> Can AutoEZ be used to model this? Yes, but only assuming that the water's edge is a straight line parallel to the Y axis. Here's a comparison of the azimuth patterns at a 10° elevation angle when a) the vertical is right at the water's edge and b) the vertical is 70 feet back from the water. Land is to the left of the Y axis and water is to the right. https://i.postimg.cc/j5RDRMGz/image.png The green dot marker is at 5° "into the water" since the water's edge is along the up/down Y axis. At that azimuth there is a 5.3 dB advantage to having the vertical at the water's edge. In contrast, looking straight out over the water (along the X axis) the advantage of being at the edge is only 0.8 dB. In the image above, a second set of azimuth ring labels (in parenthesis) has been added. This "compass rose" set of labels will help to mentally rotate the entire chart such that the water's edge (the Y axis) aligns with your physical location. Here's another image explaining that second set of labels. https://i.postimg.cc/zfrBkdD9/image.png Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Verticals on the beach
Stan Stockton wrote: Maybe someone has some idea of just how much better my signal would be if I had a 160m vertical 65 feet closer to the water? Stan, I have it on good authority that you have a modeling wizard in your back pocket. :-) So for anyone who might be interested in modeling a "Vertical on the Beach" scenario, in addition to Grant's QST article this AutoEZ page might be of interest: https://ac6la.com/aepatterns.html#Part4 Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: ON4UN (SK): Before "Low-Band DXing" there was ... what?
For the answer to that question see this tribute post by ON5AU: http://on5au.be/Homage_to_ON4UN.html Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground Conductivity
Grant wrote: >>> If you really want to know the parameters, see antennasbyn6lf.com as Rudy >>> describes techniques for ground RF properties measuring. Turns out that very subject was being kicked around on a recent qrz.com thread: https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/ Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: EZNEC
Bob wrote: >>> The problem I’m having is I can’t figure out how to separate the radials >>> from the vertical and put the source at the base of the vertical and the >>> radials. All five wires are connected and I can’t separate them. That has to be the #1 point of confusion for folks just getting started with modeling. With a "real" antenna there is a break in the wire where you want to attach the coax, like in the center of a dipole or at the base of a vertical with radials. However, with a "model" of the antenna there is *no* break in the wire. In your case the vertical wire really should be attached to the radials. You put a "source" at the point where you would normally break the wire. The source serves both to apply power to the wires and to effectively "break" the wire at that point, all in one. As Mike mentioned, one of the sample models is "Vhfgp.ez". Take a look at the source placement in that one and you'll see there is no break between the vertical and the (sloped) radials. Or take a look at sample "Bydipole.ez". Again, no physical break in the wire. You might want to also read through the "Test Drive" section in the Help. Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: K9ay loop not performing
As others have said, a good *RF* ground is a requirement. Here's a comparison of modeled elevation patterns for a K9AY loop with a very good (low impedance) RF ground vs one with a very poor (high impedance) RF ground. https://i.postimg.cc/N0MqJg0x/image.png The trick to modeling a good ground while at the same time using EZNEC "High Accuracy" (Sommerfeld-Norton) ground is explained in EZNEC Help section "Connecting to High Accuracy Ground". For AutoEZ users, *right*-click on http://ac6la.com/adhoc/K9AY_Loop.weq , choose "Save file", download to your computer, then use the AutoEZ "Open Model File" button. The K9AY_Loop.weq model makes it easy to adjust the length of the very low height radials which are used to simulate a good ground connection, as mentioned in the EZNEC help. Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: A nice grayline app and more
Marcel De Canck, ON5AU, has recently revised his website: http://on5au.be This site is a gold mine of information related to antenna modeling and radio propagation. Much of it free, the remainder very low cost. A few examples: * Just so you'll know who he is: http://on5au.be/biography.html * Review by L.B. Cebik (SK) of Marcel's propagation articles: http://on5au.be/Animations/prop_Cebic.pdf * His page devoted to grayline: http://on5au.be/Grayzone.html * Complete set of W4RNL (SK) articles: http://on5au.be/Cebik%20documents.html * Several animation "wizards" in the form of downloadable, self-contained, exe mini-programs to show gif animations. For instance: http://on5au.be/Animations/Animation%203.EXE http://on5au.be/Animations/wiz_1dec.EXE Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radial length - Oops
Oops, dupe of part of Frank's reply. My apologies. Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radial length
Also see this 2004 NCJ article by Al Christman, K3LC. http://ncjweb.com/bonus-content/k3lcmaxgainradials.pdf Dan, AC6LA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Air Wound Coil
Grant wrote: >>> Or the inverse as I did, cut my T for the low end of the band. Then three >>> series capacitors with PCB relays to short each individually (none, 1, 2, >>> or 3) yielded nearly full band coverage <1.5:1 swr. My T is 85' to top and >>> a 50:25 ohm TLT is a close match, then the capacitor stack follows. I modeled Grant's configuration with AutoEZ, mostly to see how the optimizer would handle things. I ended up with capacitor values quite different from Grant's 4000/2000/1333 pF, but part of that could be because my modeled conditions do not equal Grant's reality. Here's a full-band SWR sweep which also shows the values I used for the variables. https://postimg.cc/image/6o9yxez4h/ Bob wrote: >>> A simple T antenna will have a radiation resistance of 10-12 Ohms with >>> electrical height of say 43ft with a Good ground system of quarter wave >>> radials. So then I went back and modeled something similar to what Bob described. For this one I first optimized on both the height of the vertical portion and the length of the T arms to get a feedpoint Z very close to 12.5+j0 at 1975 kHz with no series coil. Then I optimized the inductance values for the three lower band segments all at once. https://postimg.cc/image/3u6tk1241/ AutoEZ users, if you'd like to see the optimizer setup and the trick for making the capacitance/inductance values frequency-agile just drop me a note via private email and I'll send you the models (*.weq files). Dan, AC6LA https://ac6la.com/ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Subject: 80 meter 4-square
N8PR wrote: >>> You might consider four half wave sloping dipoles with the upper end hung >>> out about 3 – 4 feet from the top of the tower. For those who enjoy antenna modeling there are a few specialized AutoEZ models available to do just that. Everything is controlled via variables so it is easy to configure the elements of the 4-square (the dipoles) in any shape that fits your circumstances. And after the geometry is set you can include a Comtek-like hybrid coupler as part of the model. That lets you see the amount of dumped power as well as other performance metrics across an entire band. Complete details and downloadable models available here: https://ac6la.com/aecollection8.html Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Adding a parasitic reflector to a vertical
For AutoEZ users: A model similar to the parasitic array that Tim described is available on this page: http://ac6la.com/aecollection8.html In the first section of that page, scroll down to topic "Parasitic Elements" and then look for the text "For a vertical parasitic example I chose a model described by N6LF ...". The sample model is for 80m but everything is controlled via variables and there are instructions (within the model itself) on how to scale for other bands. Links to several references are also included on the above page. Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: K2AV Counterpoise
K8BHZ wrote: >>> The length to avoid is nothing more than a half wavelength, which >>> translates the same impedance from end to end >>> i.e., the high Z open end translates to a high Z antenna base end. This >>> results in minimum radial current. I'm not so sure I buy that and I don't think N6LF does either. If you look at the section "An Explanation for the Dips in Ga" (Part 1, QEX pg 40) in Rudy's document http://rudys.typepad.com/files/qex-mar-apr-2012.pdf you'll find this: ["L" is the variable for radial length] Why do we see these large dips in Ga for some values of L? We can investigate this by looking at the current distributions on the radials and the associated E and H-field intensities close to ground under the radials. ... For the same current at the feed point, with longer radials the currents are much higher as we go out from the base. We would expect these higher currents to increase both E and H-field intensities at ground level under the radials. ... Since the power dissipation in the soil will vary with the square of the field intensity, it’s pretty clear why the efficiency takes such a large dip when the radials are too long. So Rudy seems to be saying that the increased loss is due to higher radial currents, not minimum radial currents. Here's an animation showing how the currents on the vertical and on 1 of 4 identical radials change as the radial length changes. Segments 1-15 are the vertical with segment 1 being the base (constant 1 amp). Segments 16-37 are the radial with segment 16 being the inner end connected to the base of the vertical. Each radial always has 0.25 amps at the inner end but the current distribution across the rest of the radial changes as the length changes. The animation frames start with a radial length 0f 0.10 WL, step by 0.02 WL, and finish at 0.60 WL. The frame where the radial current in segment #29 peaks at ~1.02A corresponds to the sharp dip in efficiency. Radial length for that frame is 0.36 WL. https://s1.postimg.org/7a7f6pvu4f/N6_LFani.gif Above is at 1.85 MHz with 4 radials at 2" above ground. Below is a different animation, this time showing E-field intensity as the radial length changes. For this animation the radial height was 10 ft so the dip occurs at ~0.45 WL (frame 9). That corresponds to the highest radial current and the max E-field. https://s1.postimg.org/45ipxxhp73/MCVert_NF3_D.gif Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: K2AV Counterpoise
This page, and the links to a couple of N6LF documents that are included there, might help: http://ac6la.com/aecollection3.html Not covered on that page are a) how the efficiency changes as the radials are placed closer to the ground, and b) whether there is any difference in best radial length for a straight vertical vs an inverted L. To address those points I ran some additional test cases at 1.85 MHz. Instead of the radial height (and base of the antenna) at 10 ft, I put the radials at a height of 2 inches. On 160m that is very close to "on ground" radials. Then I ran scenarios for a straight vertical 129.6 ft high followed by an inverted L with vertical section 60 ft and horizontal section 73 ft. Both scenarios were with just 4 radials, average ground, bare #12 copper wire. https://s1.postimg.org/3f3wirjedb/N6_LF.png Two things become obvious: 1) As the radial height is lowered the "length to avoid" gets shorter. When the radials are at 10 ft the large drop in efficiency happens at a radial length of ~0.47 WL (~250 ft at 1.85 MHz). When the radials are at 2 inches the efficiency dip happens at a radial length of ~0.36 WL (~191 ft). 2) For both the straight vertical and the inverted L, the highest efficiency happens at a radial length of ~0.2 WL (~106 ft). But if you make them shorter, say the length of the vertical portion of the inverted L (60 ft, ~0.11 WL), you're really not giving up very much. For AutoEZ users, also see the 3rd section on this page: http://ac6la.com/aecollection8.html Model "Vertical with Tapered Seg Radials.weq" uses tapered segment lengths which greatly reduces the number of segments and hence the calculation times. If you'd like a copy of the model used to produce the above chart, drop me a note off-list. Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160M 8 Circle Array for transmit
Rick Karlquist wrote: >>> Models well on EZNEC. There are some fairly detailed 8-circle modeling studies in the last section on this page: http://ac6la.com/aecollection6.html Lots of illustrations and several url links for more info. Dan, AC6LA http://ac6la.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Which 4 directions?
Frank wrote: A 160 meter receiving 4-square can be built with verticals as short as 20 feet and can be built with 80 foot sides, or even smaller. Azimuth and elevation patterns for a few typical arrays can be found in the last section on this page: http://ac6la.com/aecollection6.html At the bottom of that section you'll also find various reference links, including Frank's 2014 Contest Univesity presentation that Jim just mentioned. Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Which 4 directions?
Mike Waters wrote: If anyone has patterns for those, that would be interesting. I haven't yet written a typical AC6LA more words than any human should be forced to read at one time example, but this post to the Shared Apex Loop Array Yahoo group shows some pattern comparisons: https://groups.yahoo.com/neo/groups/sharedapexloop/conversations/messages/568 Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: ZS6BKW
Marsh Stewart wrote: I found a website with detailed info on the ZS6BKW antenna. Another nice analysis of the ZS6BKW was done a while ago by K4SAV over on qrz.com: http://forums.qrz.com/showthread.php?442166-Which-is-better-G5RV-or-ZS6BKW Jerry showed pattern comparisons but did not include any SWR comparisons. That was done in a follow-up post which also included comparisons of total feedline loss (matching section plus coax): http://forums.qrz.com/showthread.php?442166-Which-is-better-G5RV-or-ZS6BKWp=3206821#post3206821 Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Antenna patterns (in close)
AutoEZ can display near field data on polar, rectangular, and 3D plots. For several illustrated examples see section Electric or Magnetic Field Strength - Near Field here: http://ac6la.com/aepatterns.html AutoEZ home page: http://ac6la.com/autoez.html Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Looking for 160m narrow beam RX advice
IV3PRK has several interesting papers available as links from this page http://www.iv3prk.it/TX3A-DHDL.htm including one which compares both a single DHDL and a dual DHDL with a Waller Flag. Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling W8JI and Hi-Z 8 Circles
Based on some user feedback, the 8-circle models mentioned earlier have been modified with an additional variable to control the azimuth direction of the main lobe. That lets you change the direction just by changing (or doing a sweep on) a single variable. So you can easily: 1) see how the azimuth patterns overlap as the array is steered in 45° steps, and 2) compare patterns against other models which may be fixed in a particular direction. For case 1, here's how the Hi-Z type (8 elements in use) 8-circle array patterns would overlap as you turn the knob on the control box. This is for a 200 ft diameter array with ±106° phasing, 20° TOA for the patterns. Compass rose angles are shown in parenthesis. http://ac6la.com/adhoc/8circle7.png For case 2, this is how a W8JI type (aka BroadSide/End-Fire or BSEF, 4 elements in use) 8-circle array with 0.604 wl broadside spacing and 125° phasing compares against a 4-square receiving array with 0.125 wl element spacing and Crossfire feeding. Both arrays use the same basic element, the top hat model rxvrhat.ez from Tom's page. At a 20° TOA the 4-square has a gain of -22.43 dBi compared to -10.95 dBi for the 8-circle. (But the RDF is only about 1 dB lower for a diameter of 94 ft compared to 348 ft for the 8-circle.) In order to get an accurate comparison of the pattern *shapes* on a common polar chart, the *gain* of the 4-square has been normalized to that of the 8-circle by reducing the value of the swamping resistors. Original gain below on left, normalized gain below on right. http://ac6la.com/adhoc/8circle8.png The 4-square can be fed either as Crossfire or BroadSide/End-Fire using exactly the same phasing lines, a neat idea picked up from IV3PRK. In the patterns below, the swamping resistors are back at the normal values (to give 75+j0 at the feedpoint for a standalone element). With Crossfire feeding the gain at 20° TOA is down 7.45 dB compared to BSEF feeding but the RDF is 2.1 dB better, below left. Note that a design criteria for IV3PRK was good rejection at backside 45°, below right. http://ac6la.com/adhoc/8circle9.png For more details on this dual-feed 4-square see the Receiving Antennas portion of the IV3PRK site and follow the links on the left side of the page. http://www.iv3prk.it/rx-antennas.htm Finally, thank you Jim Brown for mentioning the 2014 Contest University W3LPL Receiving Antennas presentation. Lots of good info there. Here's the direct link. http://www.contestuniversity.com/attachments/W3LPL_Receiving_Antennas_2014.pptx These are the revised 8-square models with the additional variable to change the pattern direction. http://ac6la.com/adhoc/W8JI_8_Circle__TopHat.weq http://ac6la.com/adhoc/W8JI_8_Circle__AL-24.weq http://ac6la.com/adhoc/Hi-Z_8_Circle__TopHat.weq http://ac6la.com/adhoc/Hi-Z_8_Circle__AL-24.weq And here's the 4-squareRX model with a variable that switches between Crossfire feed and BSEF feed. http://ac6la.com/adhoc/4SquareRX__TopHat.weq Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Modeling W8JI and Hi-Z 8 Circles
The recent thread on 8 circle arrays prompted me to create a few different AutoEZ models, mostly because I was curious about the relationship between array size, element phasing, and number of active elements (4 with W8JI, 8 with Hi-Z). First thing I did was educate myself. For W8JI type arrays: http://w8ji.com/small_vertical_arrays.htm http://n3ujj.com/manuals/8%20Circle%20Vertical%20Array%20for%20Low%20Band%20Receiving.pdf http://www.dxengineering.com/parts/dxe-rca8b-sys-3p http://static.dxengineering.com/global/images/instructions/dxe-rca8b-sys-3p-rev3.pdf Low-Band DXing, 4th ed, ON4UN, Chapter 7, Sections 1-21 and 1-30 And for Hi-Z type arrays: http://www.k7tjr.com/need.htm http://www.kkn.net/dayton2014/HiZ_DAYTON_2014_7n2.pdf http://www.hizantennas.com/HiZ8-16080_users_guide.pdf http://www.hizantennas.com/Hiz_8_16080_manual.pdf http://www.dxengineering.com/parts/hiz-8a-lv2-160-2 Then I created models where the array size (diameter) can be controlled via a single variable, along with another variable to control the phasing. For example, here's the AutoEZ Variables sheet tab for a W8JI type array. The Hi-Z is similar except that array size is specified in feet (or meters) rather than wavelengths. http://ac6la.com/adhoc/8circle1.png Since everything is controlled by variables you can run variable sweeps changing one or more parameters. Here's the W8JI array with the spacing (B) held constant while the phase delay (P) is swept from 80 to 140 degrees. For each test case AutoEZ will automatically calculate the RDF (last column). http://ac6la.com/adhoc/8circle2.png When the calculations finish you can step through the 2D patterns. Here are the elevation and azimuth (at 20° TOA) patterns for 0.604 wl broadside spacing and 125 degree phasing, as shown by B and P in the lower right corner. http://ac6la.com/adhoc/8circle3.png You can run similar sweeps changing the array size while holding the phase delay constant, or hold both size and phase constant and do a frequency sweep, or use the Generate Test Cases button to create any combination. For example, the setup below would vary broadside spacing B from 0.50 to 0.70 wavelengths; for each B the phase delay P would be varied from 115 to 135 degrees; all at a constant frequency of 1.85 MHz. That would be 25 test cases. You can run thousands if you like. http://ac6la.com/adhoc/8circle4.png You can also show 3D patterns. Here's an example of a Hi-Z array, diameter 200 ft with ±106 degree phasing, along with the 2D elevation pattern. http://ac6la.com/adhoc/8circle5.png And here's how the RDF for a 200 ft Hi-Z array varies as the phase is swept from ±100 to ±112 degrees. http://ac6la.com/adhoc/8circle6.png For both of the array types, I created one model using W8JI-style top hat loaded vertical elements (per the sample model on Tom's site) and a second model using simple aluminum tube elements (per the four-section, 23.25 ft, Hi-Z AL-24). Here are the models. Save to your computer then use the AutoEZ Open Model File button. http://ac6la.com/adhoc/W8JI_8_Circle__TopHat.weq http://ac6la.com/adhoc/W8JI_8_Circle__AL-24.weq http://ac6la.com/adhoc/Hi-Z_8_Circle__TopHat.weq http://ac6la.com/adhoc/Hi-Z_8_Circle__AL-24.weq Please note that these models have not been reviewed or approved by the authors of the references cited above. Any mistakes or misinterpretations are strictly mine. And the models may or may not be an accurate representation of any given commercial package. In all the models, a single variable (X) controls the segmentation. You can reduce that to speed up the calculations. You can also run a sweep on X to do a convergence test for model accuracy. For comparison with the 8 circle arrays, here's the W8WWV Benchmark Beverage model. With this one you can sweep the length and/or other parameters. http://ac6la.com/adhoc/W8WWV_Beverage.weq Greg's Beverage page for reference. http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/Beverage.htm Calculated results for this Beverage are shown in section Calculate 3D Data here. http://ac6la.com/aeuse3d.html === AutoEZ is an antenna modeling program which uses Microsoft Excel in combination with EZNEC. http://ac6la.com/autoez.html Current AutoEZ users, see here for recent maintenance updates and instructions on how to get the latest release. http://ac6la.com/aechanges.html Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Balun or no balun
Tom wrote: A resonant 160 meter loop around 20-30 feet above the ground has a feedpoint impedance of around 50 ohms on 160, and about 80 ohms on 80 meters. The antenna impedance isn't really high until 40 meters, where it would be resonant far outside the band and have a terrible mismatch to any feedline. Expanding a bit on what Tom said, the source resistance at resonance will also depend on the type of ground. With AutoEZ, I first used this dialog to create a 4-sided horizontal loop having a perimeter of P ft at a height of H ft above ground. http://ac6la.com/adhoc/160mLoop1.png I then created a series of test cases with H ranging from 10 to 90 ft (~0.02 to 0.16 λ at 1.8 MHz) in 5 ft steps and with P having an initial value of 560 ft (~1005/Freq). Then the Resonate button was used to automatically adjust the loop perimeter P for resonance at each height. http://ac6la.com/adhoc/160mLoop2.png Repeating that process for three different ground types gives this result for the source resistance. http://ac6la.com/adhoc/160mLoop3.png With the perimeter frozen at 560 ft, on 40m the loop will not be resonant, as Tom said. The source *reactance* will be a few hundred ohms negative. The source *resistance* will look like this. http://ac6la.com/adhoc/160mLoop4.png On the other hand, if you calculate the source resistance for a 40m *resonant* loop (*not* the scenario that the OP described nor which Tom addressed but just to illustrate), where the loop perimeter is ~145 ft and where 90 ft above ground is ~0.65 λ instead of ~0.16 λ, you'll get this. http://ac6la.com/adhoc/160mLoop5.png If you'd like to duplicate these results, or run calculations for a different band, the following model file is suitable for use with the free demo version of AutoEZ (http://ac6la.com/autoez.html). You'll also need EZNEC and Microsoft Excel. http://ac6la.com/adhoc/160mLoop.weq Download that file, use the AutoEZ Open Model File button to open it, tab to the Calculate sheet, select all the P values (cells D11-D27), and click the Resonate button. Or change all the frequencies to your new choice and set all the initial P values to ~1005/Freq (initial value not critical), then click Resonate. Or just set all the frequencies and P values as desired and click Calculate All Rows instead of Resonate. In any case, make sure EZNEC is already open in a separate window beforehand. When the calculations finish tab to the Custom chart sheet. Select R at Src for the chart Y axis and Variable 1 (which is H, height) for the chart X axis. Dan, AC6LA http://ac6la.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 160 GP Choke
W0BTU was kind enough to include a link to his inverted-L EZNEC model so I added that to a thread over on eHam which discusses using a dual-band autopilot matching network, in this case using the inverted-L on 160 and 80 with no tweaking or switching of the matching network needed: http://www.eham.net/ehamforum/smf/index.php/topic,99152.0.html Nothing to do with chokes, just thought it might be of interest. Dan, AC6LA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Matching network info for 80 160M needed
Nermin wrote: There was an article in recent issue of ARRL QST, A 20 and 40 meter Vertical on Autopilot, ... That article by K6MHE is available here: http://k6mhe.com/files/DualBandVert.pdf And here's a blog entry and a corresponding YouTube video by AB8XX for a similar 80m/40m antenna: http://ab8xx.blogspot.com/2008/12/80m40m-dual-band-vertical.html https://www.youtube.com/watch?v=WMfI_WRAIYQ This entire system, antenna plus autopilot matching network, can be modeled using AutoEZ and the EZNEC L Networks feature. A conventional low pass L network has an inductor in the series branch and a capacitor in the shunt branch. However, EZNEC L networks can have compound components in each branch. Hence the matching network can be modeled like this (from the K6MHE article). http://ac6la.com/adhoc/DualBand1.png Here is the AutoEZ L Networks table with variables K-L-M being used for the component C1-L1-C2 values. The source is on V1, the network input port. The network output port is the antenna feedpoint. http://ac6la.com/adhoc/DualBand2.png The following extract from the AutoEZ Variables sheet tab shows the initial values for the K6MHE 40m/20m setup. Instructions for setting the initial network component values (variables K-L-M) are found in additional comments on the sheet, not shown. Note that ground loss due to a less than perfect radial field is simulated using variable D in conjunction with MININEC-type ground; actual radials are not included in the model (although you may add them if you wish and change to High Accuracy ground). Approximate ground loss values are: 4 radials, 29 ohms; 8 radials, 18 ohms; 16 radials, 9 ohms; 32 radials, 4 ohms. http://ac6la.com/adhoc/DualBand3.png With the C1-L1-C2 component values as set above, the L network look like this when the model is passed to EZNEC. http://ac6la.com/adhoc/DualBand4.png Once the initial network values are set, the AutoEZ optimizer can be used to adjust components C1, L1, and C2 (variables K-L-M) to produce the lowest possible SWR at the two midband frequencies. http://ac6la.com/adhoc/DualBand5.png After optimization, here are the final SWR values for seven 40m frequencies and eight 20m frequencies. This is similar to Fig 5 in the K6MHE article except that all frequencies are shown on a single chart. (Blue markup added for clarity.) http://ac6la.com/adhoc/DualBand6.png Doing the same kind of analysis for 160m/80m (with radiator length B = 132 ft) gives these SWR values, this time shown with a different scale for SWR (on the right). The midband SWR values are fine (remember, right scale) but because of the relatively wider widths of 160 and 80 the band edge SWR values are higher. http://ac6la.com/adhoc/DualBand7.png Of course it would be possible to use relays to implement two different autopilot matching networks, one for the low end of 160 and 80 and a second for the high end of the bands; I didn't model that. For those who already have AutoEZ (http://ac6la.com/autoez.html) or who would like to experiment with the free demo version, here is the model used for this study. http://ac6la.com/adhoc/DualBandVert.weq Download that file, use the Open Model File button, then tab to the Variables sheet to get started. As downloaded, the model is ready to be optimized (Optimize tab, Start button) and then calculated over multiple frequencies (Calculate tab, Calculate All button). The number of segments has been set to allow use with the free demo version. I'll be happy to answer any questions even if you are using the demo version of AutoEZ. One last thing. Nermin, S58DX, has a really cute Golden Retriever: http://files.qrz.com/x/s58dx/21022011022.jpg Being a dog lover I just had to include that link! Dan, AC6LA http://ac6la.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Low-angle radiation from vertical antennas
This is somewhat related to the vertical on a beach thread but I figured if I put that in the subject line I might get lynched. In the past there have been questions about the accuracy of NEC far field calculations at low take-off angles for vertical antennas since the far field does not include the ground wave. To help resolve the issue I modeled a λ/4 vertical with and without the ground wave at multiple slant (radial) distances and plotted the results. This is for the 160m band at 10°, 1°, and 0.1° take-off angles with slant (radial) distances varying from 100 m to 100 km: http://ac6la.com/adhoc/VertFlds9.png And this is for 40m: http://ac6la.com/adhoc/VertFlds10.png As expected, the far field values decay at a 1/r rate. With log-log scales that's a one decade decrease for every one decade increase in radial distance. At close-in distances the far field does indeed under-estimate the total field which includes ground wave. However, for typical sky wave propagation the difference has vanished (plot lines converged) long before the ionosphere has been reached. For each of the 3 take-off angles, calculations were done at 100 different distances in order to get smooth curves. Obviously I didn't do those one at a time; I used AutoEZ with 100 test cases. Each test case generated an EZNEC Setups Near Field like this. http://ac6la.com/adhoc/VertFlds5.png Near Field calculations report the total field, including the ground wave, and are valid at any distance from the antenna. For the Far Field, also done for each test case, AutoEZ can convert the dBi values produced by EZNEC to the corresponding mV/m field strengths. Dan, AC6LA http://ac6la.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Modeling the proverbial vertical on a beach
The latest AutoEZ update includes the ability to create EZNEC models having 2 separate ground media. One typical use is to model a vertical located on a sandy beach next to salt water. Using AutoEZ you can assign a variable to the media 2 linear boundary and then run a series of test cases with different values for the boundary coordinate. Here is an animation of how the pattern for a 20m quarter-wave vertical changes as the distance to the water is varied from 0 to 100 feet. http://ac6la.com/aepatani5.gif For more information see Using 2 Ground Media here: http://ac6la.com/aepatterns.html Current AutoEZ users, there is no charge for AutoEZ updates. See here for a list of recent changes: http://ac6la.com/aechanges.html Dan, AC6LA http://ac6la.com _ Topband Reflector Archives - http://www.contesting.com/_topband
