Re: Topband: trimming elevated radials
I wouldn't attempt to tune the radials exactly to resonance, because that will be most difficult to achieve due to a number of reasons... the worst that may happen is that just one radial is exactly resonant, as it will take (almost) all the return current and diminish the effect of (horizontal) cancellation... make them all a little longer (or shorter) and tune the radiator for resonance... My models do not seem to show any special advantage to doing that. If they are not symmetrical, current still seems to get uneven. Is there data somewhere that shows it promotes balanced currents? All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: trimming elevated radials
Thanks Dan, very excellent stuff (as you always do!!!). Your observation of the large shift in currents with small changes in length is exactly the problem I am concerned with. And the N6LF data shows the problems with asymetrical radials. So my question was how to make uniform the currents without having to simultaneously measure and iteratively trim for uniformity. I have gear to measure 6 radials at one time - but that brute-force method seems less than elegant. There have been quite a few comments back on this and while there are some articles published on this (beyond the N6LF QEX stuff from last year), but they seem to not be well known; KE7BT and K5UI. 73/jeff/ac0c www.ac0c.com alpha-charlie-zero-charlie -Original Message- From: Dan Maguire Sent: Sunday, March 31, 2013 2:40 AM To: topband@contesting.com Subject: Re: Topband: trimming elevated radials Jeff Blaine wrote: What is the preferred method of tuning elevated radials for uniformity? [snip] ... There are two methods that I thought of. Measuring the current at the base of the vertical/radial union and trimming lengths iteratively trying to get a uniform current reading on all elements. [snip] ... Lacking a good answer to Jeff's question about the preferred method of insuring uniformity in elevated radials I decided to look at the problem from the other direction. That is, intentionally make the radials non-uniform and then see what the difference in current magnitude/phase would be at the innermost point of each radial. I started with EZNEC sample model ELEVRAD2.ez. This model was developed by W7EL to demonstrate the correct way to model radials close to ground, so the first thing I did was raise the entire model by 120 inches. With a 1 amp source the current distribution as shown by EZNEC is: http://ac6la.com/adhoc/AsymRadials1.png Looking at the same data charted a different way confirms the expected symmetry. The yellow info boxes show the Wire number (W), Segment number (S), current magnitude, and current phase for selected segments as marked with the green dots: http://ac6la.com/adhoc/AsymRadials2.png Note that in the second chart the shape of the curve does *not* match the physical position of the segments. That's because in this particular model the segments do not have a uniform length. However, the magnitude/phase results are as expected; 1 amp at the source (Wire 1 Segment 2 [W1 S2]) and 0.25 amps at the inner end of each radial (such as Wire 9 Segment 1 [W9 S1]). Next I modified the model to make the length of the two adjacent radials along the +X and +Y axes be 95% of the original length (1482 vs 1560 for the radials along the -X and -Y axes). As expected the radiation pattern is now a bit skewed. Here's the azimuth pattern at 24 deg elevation angle: http://ac6la.com/adhoc/AsymRadials3.png And here's the rectangular plot of the pattern instead of the polar plot: http://ac6la.com/adhoc/AsymRadials4.png The really interesting result is how much the current on the radials has changed given just a 5% difference in length. Wire 9 Segment 1 [W9 S1] is the inner end of one of the shortened radials, W 27 S 1 is the inner end of one of the original length radials: http://ac6la.com/adhoc/AsymRadials5.png Jeff has some pretty fancy magnitude and phase measuring equipment developed in cooperation with Greg Ordy, W8WWV. Given the substantial changes in the current at the inner ends of the radials with just a 5% difference in lengths it seems reasonable that he could detect much smaller differences in non-uniformity of the radials. Of course, the part about trimming lengths iteratively might be more challenging. :) Blatant plug: Most of the charts shown above were created with the AutoEZ program. See http://ac6la.com/autoez.html for more information. Dan, AC6LA http://ac6la.com/ All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: trimming elevated radials
What is the preferred method of tuning elevated radials for uniformity? Hi Jeff, I'd say make the radials longer than you expect them to be, put on a carrier, and see if you can light a neon bulb at the end of a stick out at the end. As you approach the feedpoint the voltage will go through a null then start back up again. Cut the wire so that doesn't happen. This should work in theory. In practice I don't know. You get what you pay for in advice ! Rick K2XT All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: trimming elevated radials
I dont know if this is the preferred method but here is what I do. Before connecting the vertical I attach my SWR meter to the radials by pairs, just like tuning a dipole, pruning the radial pairs to resonance at my desired frequency. Then I connect the radials together and attach the SWR meter between the connected together radials and the vertical and prune the vertical for resonant freq. Bob K6UJ On Mar 29, 2013, at 9:56 AM, Jeff Blaine wrote: What is the preferred method of tuning elevated radials for uniformity? I realize you can measure the lengths, try to get uniform heights, etc so that you match the model as close as possible. However, it seems that this is good only to the first approximation. There are two methods that I thought of. Measuring the current at the base of the vertical/radial union and trimming lengths iteratively trying to get a uniform current reading on all elements. The second one was to disconnect all the radials. And then connect them one-by-one, trimming for the same resonance point for the single radial+vertical as a pair. 73/jeff/ac0c www.ac0c.com alpha-charlie-zero-charlie All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: trimming elevated radials
Jeff Blaine wrote: What is the preferred method of tuning elevated radials for uniformity? [snip] ... There are two methods that I thought of. Measuring the current at the base of the vertical/radial union and trimming lengths iteratively trying to get a uniform current reading on all elements. [snip] ... Lacking a good answer to Jeff's question about the preferred method of insuring uniformity in elevated radials I decided to look at the problem from the other direction. That is, intentionally make the radials non-uniform and then see what the difference in current magnitude/phase would be at the innermost point of each radial. I started with EZNEC sample model ELEVRAD2.ez. This model was developed by W7EL to demonstrate the correct way to model radials close to ground, so the first thing I did was raise the entire model by 120 inches. With a 1 amp source the current distribution as shown by EZNEC is: http://ac6la.com/adhoc/AsymRadials1.png Looking at the same data charted a different way confirms the expected symmetry. The yellow info boxes show the Wire number (W), Segment number (S), current magnitude, and current phase for selected segments as marked with the green dots: http://ac6la.com/adhoc/AsymRadials2.png Note that in the second chart the shape of the curve does *not* match the physical position of the segments. That's because in this particular model the segments do not have a uniform length. However, the magnitude/phase results are as expected; 1 amp at the source (Wire 1 Segment 2 [W1 S2]) and 0.25 amps at the inner end of each radial (such as Wire 9 Segment 1 [W9 S1]). Next I modified the model to make the length of the two adjacent radials along the +X and +Y axes be 95% of the original length (1482 vs 1560 for the radials along the -X and -Y axes). As expected the radiation pattern is now a bit skewed. Here's the azimuth pattern at 24 deg elevation angle: http://ac6la.com/adhoc/AsymRadials3.png And here's the rectangular plot of the pattern instead of the polar plot: http://ac6la.com/adhoc/AsymRadials4.png The really interesting result is how much the current on the radials has changed given just a 5% difference in length. Wire 9 Segment 1 [W9 S1] is the inner end of one of the shortened radials, W 27 S 1 is the inner end of one of the original length radials: http://ac6la.com/adhoc/AsymRadials5.png Jeff has some pretty fancy magnitude and phase measuring equipment developed in cooperation with Greg Ordy, W8WWV. Given the substantial changes in the current at the inner ends of the radials with just a 5% difference in lengths it seems reasonable that he could detect much smaller differences in non-uniformity of the radials. Of course, the part about trimming lengths iteratively might be more challenging. :) Blatant plug: Most of the charts shown above were created with the AutoEZ program. See http://ac6la.com/autoez.html for more information. Dan, AC6LA http://ac6la.com/ All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
