Re: Topband: My Turn For a Brain Pick - Sanity Check
Hi Jim How well did you do on FieldDay? How well did the 2 element vertical array perform? -- Jim K9TF _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Right. There's some discussion of this in the ON4UN book, where I found the Christman matching. As published there, it's 84 degrees of 50 ohm line in each element, plus 71 degrees of 50 ohm line in the element facing the desired forward direction,change directions by switching the 71 degree section. So the forward element is actually feed at 155 degrees? Phase shift is NOT the length of a transmission line unless the line has 1:1 SWR, is lossless, and/or is a multiple of 90 degrees. In a phased array, with equal 90 degree lines feeding each element, the lines cancel out. Phase shift modification between elements caused by the feedlines to the elements is zero. In the Christman system, or any system where lines are not 90 degrees or multiples of 90 and are also mismatched, the two 84-degree lines do not quite cancel each other out. They reduce the effect of each other, but not to zero like a 90 line or a matched line. They do add some phase shift, but certainly nowhere near 84 degrees. Also the 71 degree line, since it is not 90 and not matched, does not shift phase 71 degrees. Adding the line lengths together without considering impedance and transmission line effects doesn't work. It is really a more complex answer that requires looking at the system. Voltage and current are not even in phase, so we also have to know if the element is driven by voltage, current, or someplace between. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Jim Sounds like you have a great 40M antenna for filed Day. QRP sounds like fun. All you need now is brats and beer and something to keep you warm at night. Right. There's some discussion of this in the ON4UN book, where I found the Christman matching. As published there, it's 84 degrees of 50 ohm line in each element, plus 71 degrees of 50 ohm line in the element facing the desired forward direction,change directions by switching the 71 degree section. So the forward element is actually feed at 155 degrees? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 3:34 PM, Tom W8JI wrote: I can't think of a reason to pick 90 degrees as a target value, unless it is a system designed to protect something on groundwave that happens to be straight in line with the elements. I agree. For me, the primary design objectives are maximizing forward gain, beamwidth, and gain bandwidth. I don't care about F/B. 73, Jim K9YC Ditto as Ive already mentioned as F/R isnt useful to me since I have several receiving antennas. Gain variation with reasonable lengths of coax are miniscule and its not being wasted in a hybrid either. Carl KM1H All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
I agree. For me, the primary design objectives are maximizing forward gain, beamwidth, and gain bandwidth. I don't care about F/B. Null depth is maximum when radiation is equal from the two elements, and that occurs with equal effective ampere-feet in the antennas. Equal construction antennas require equal current. The current ratio controls null depth. Maximum effective front-to-rear and maximum gain always occurs at some phase shift more than 180 - spacing. So if spaced 45 degrees, maximum effective F/R (deepest usable null depth off the back) and maximum gain is some phase shift more than 180-45 = 135, or in the case of 1/4 wave spacing more than 180 - 90 = 90. Phase positions the nulls. I can't imagine anyone would want one single-point null at zero elevation off the back, when they could have a null cone that is just as deep and covers a very wide area, or why they might want less gain, since they get more gain with that null cone that gives much better F/R. Perhaps the problem is years and years of not wording things properly in our handbooks, or not thinking through the problem, has confused people. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 3:34 PM, Tom W8JI wrote: I can't think of a reason to pick 90 degrees as a target value, unless it is a system designed to protect something on groundwave that happens to be straight in line with the elements. I agree. For me, the primary design objectives are maximizing forward gain, beamwidth, and gain bandwidth. I don't care about F/B. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Right. There's some discussion of this in the ON4UN book, where I found the Christman matching. As published there, it's 84 degrees of 50 ohm line in each element, plus 71 degrees of 50 ohm line in the element facing the desired forward direction,change directions by switching the 71 degree section. It is critical to understand that a 71 degree line does not necessarily delay phase 71 degrees. Also, if the lines to the elements are not multiples of 90 degrees, those lines will alter phase relationship between the two elements based on the impedance mismatch on the lines. Since the elements in a two element unidirectional array have grossly different impedances, and since the lines to the elements are not multiples of 90 degrees, phase delay and current distribution changes in the element feedlines themselves are different. This means we cannot look at the system and conclude anything. Along the same note, almost every Ham transmitting antenna setup I have seen does not have the phase shift and current ratios the builders or designers think. It's common to think a hybrid gives 90-degrees phase shift, that a 3/8th line gives 135 degrees delay, and other similar thingsbut that rarely is true. It might, but a cardioid with a null at zero degrees elevation straight off the back is a pretty poor pattern for skywave use, as well as for gain. Gain increases and the effective or useful F/R ratio increases significantly when phase shift between the elements is some value greater than 90 degrees. I can't think of a reason to pick 90 degrees as a target value, unless it is a system designed to protect something on groundwave that happens to be straight in line with the elements. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 10:10 AM, Jim GM wrote: What kind of gain readings are you getting now? We didn't measure gain, but we did measure F/B. Gain is rather difficult to pin down. Even F/B is tricky -- there was at least 6dB of QSB on the rear setup (with the 71 degree line traded to the other element). Measurement distance was 5 miles mid-afternoon. BTW -- many thanks for all the helpful ideas. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 10:18 AM, Jim GM wrote: Sounds like your gearing up for Field Day. If so where are you going to set up? With the K6MI "Chews Ridge Gang," about 50 miles E of Monterey, CA. We do QRP battery. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
I guess 90 degree phase shift might result in a cardioid pattern? Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Wednesday, June 12, 2013 2:58 PM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check > Christman phasing is at 71 degrees? I was thinking 90 degree phasing. > Whats the reasoning for this? Optimum phasing of two verticals 1/4 wave apart is never 90 degrees, unless the user for some reason wants a single-point zero-angle null and less than maximum gain. Optimum element current delay for Ham use is always more than 90 degrees, and generally around 110-120 degrees, with 1/4 wave spacing. Making things more complex, phase shift in a delay line is never the line length unless the line is either 1/4 wave long or a multiple of 1/4 wave, or the line has a reasonably well-matched termination. With that in mind, a 71 degree long line might produce considerably different phase shift than the electrical line length, and the user probably wants phase to be some other value than 90 degrees (if the user understands arrays and patterns). 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 11:58 AM, Tom W8JI wrote: Christman phasing is at 71 degrees? I was thinking 90 degree phasing. Whats the reasoning for this? Optimum phasing of two verticals 1/4 wave apart is never 90 degrees, unless the user for some reason wants a single-point zero-angle null and less than maximum gain. Optimum element current delay for Ham use is always more than 90 degrees, and generally around 110-120 degrees, with 1/4 wave spacing. Making things more complex, phase shift in a delay line is never the line length unless the line is either 1/4 wave long or a multiple of 1/4 wave, or the line has a reasonably well-matched termination. With that in mind, a 71 degree long line might produce considerably different phase shift than the electrical line length, and the user probably wants phase to be some other value than 90 degrees (if the user understands arrays and patterns). Right. There's some discussion of this in the ON4UN book, where I found the Christman matching. As published there, it's 84 degrees of 50 ohm line in each element, plus 71 degrees of 50 ohm line in the element facing the desired forward direction,change directions by switching the 71 degree section. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Christman phasing is at 71 degrees? I was thinking 90 degree phasing. Whats the reasoning for this? Optimum phasing of two verticals 1/4 wave apart is never 90 degrees, unless the user for some reason wants a single-point zero-angle null and less than maximum gain. Optimum element current delay for Ham use is always more than 90 degrees, and generally around 110-120 degrees, with 1/4 wave spacing. Making things more complex, phase shift in a delay line is never the line length unless the line is either 1/4 wave long or a multiple of 1/4 wave, or the line has a reasonably well-matched termination. With that in mind, a 71 degree long line might produce considerably different phase shift than the electrical line length, and the user probably wants phase to be some other value than 90 degrees (if the user understands arrays and patterns). 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Read and envy: http://shakespeare-military.com/masts.asp They take Visa and Mastercard! Tim N3QE -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim GM Sent: Wednesday, June 12, 2013 1:19 PM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check I have seen some thing like those military surplus mast sections. I believe the ones I saw were made by Shakespear. I think this is the same company that made those good trout fishing rods and reels like the one I have. Sounds like your gearing up for Field Day. If so where are you going to set up? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
I have seen some thing like those military surplus mast sections. I believe the ones I saw were made by Shakespear. I think this is the same company that made those good trout fishing rods and reels like the one I have. Sounds like your gearing up for Field Day. If so where are you going to set up? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Very fine Jim. What kind of gain readings are you getting now? Christman phasing is at 71 degrees? I was thinking 90 degree phasing. Whats the reasoning for this? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/11/2013 9:24 AM, Jim GM wrote: So Jim, what are your final conclusions? I was convinced by K2AV that the Yagi idea (passive reflector) was a bad idea because it is too sensitive to ground characteristics. I went to the Christman phasing method and it plays nicely. Another mistake I made in NEC was trying to model the radials a fraction of an inch above High Accuracy Ground (I'm using the NEC2 engine), so I was making the elements too long. I switched to a much simpler model with the MiniNEC ground model, the elements grounded with a source at the bottom, and a small resistance load to simulate ground losses. That gave me numbers for element lengths that correlated well with measurement (one element in place at a time). The physical implementation of this antenna is pretty slick. We're using the military surplus tubular metal mast sections, supported by the standard tripod base fixture, with sections of PVC mast section as each leg of the tripod. There are several vendors who sell these parts mail order or on the net (several are usually at Dayton). Each mast section has an overall length of 4 ft, but you lose 4 1/2 inches when you mate the sections. One person can raise an element unassisted -- the tripod section is about 5 ft off the ground, so you simply insert sections from below, push them up, add the next. We have also used this mast construction to support small tri-banders and even inverted V dipoles for FD and CQP. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
So Jim, what are your final conclusions? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Regarding how the RBN works: You will be re-spotted if you change frequency (more than about 0.1 kHz), or after 10 minutes. Note that due to QRN/QRM/QSB, some Skimmers may not hear you the first time you call. For this type of testing, you might want to call several times in a row, on the same frequency. The RBN team suggests using the keyword TEST instead of CQ for this type of testing. For example: TEST TEST ZL2HAM ZL2HAM You will get the best results if you use the same WPM for all words (or use a keyer). Keep in mind that many RBN nodes, including mine, only listen on 80 and 160 during their local night -- so calling at different times may well result in different Skimmers hearing you. You might also consider using my ViewProp tool to help visualize Skimmer locations and spots. See http://zl2ham.wikispaces.com/ 73, Rick ZL2HAM -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim GM Sent: Saturday, June 08, 2013 4:14 AM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check I think your too close to tell, or just coupling into every thing around there. Knowing you I am sure you have done every thing right. Try calling CQ during day light hours and see what signal strengths the Reverse beacons give you. http://www.reversebeacon.net/main.php Problem with doing this is the beacons may not re-spot you until your off the air for say 15 minutes or shift frequency. I do not know how they really tick. -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
See correction below in RED. Looks like the Reflector wouldn't pass the EZNEC attachment. I'll have to forward that in separate e-mails - not on the reflector -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Charlie Cunningham Sent: Friday, June 07, 2013 4:05 PM To: 'Jim GM'; 'topband'; Tom W8JI Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check Hi, Jim I'm most suspicious regarding your radial systems: * Are your radials resonant? For the purposes that you are attempting, they need to be, in order to maintain the phase relationship between the driven element and the parasite. * Are your radials elevated? * Do your radial systems overlap or pass close to each other?? You can have considerable unintended and competing coupling via the radials that can destroy the parasitic relationship between the driver and parasite. I am attaching and EZNEC file of a 5-element 80m array that I designed and built some years ago, for a friend, Jim, W4RS, when he was in Virginia. It was a wonderful "kick-ass" "knock-'em-dead" antenna for tough long-haul international DX paths and a real "pile-up buster"! If you have access to EZNEC you can have a look. It consists of a central GP with 4 parasites arranged around it in a square. Each of the parasites has a 6 ft shorted line of 450 ohm ladder line at the base. The inductance of the 6 ft shorted line tunes the parasite as a REFLECTOR director. Then the shorted line can be shorted an inch or so from the attach point at the vertical element and the radials, to switch it to director tuning. The result is that in the diagonal directions the array basically operates as vertical 3-element 1/2 yagi. In the N/S/E/W directions it operates as two horizontally stacked 3-element 1/2 yagis that share a common driver. If you have access to EZNEC. Please examine how I handled the resonant radials. The central GP driver has 4 elevated resonant radials that extend outward past the parasites. The parasites each have two resonant elevated radials that are at right angles to one another and are led away from the center of the array to minimize the radial coupling. The result was a "killer" 80m DX array that was the envy of a few serious 80m DXer down here in our area. If you want to play the beam steering, go into the "Transmission Lines" menu in EZNEC and switch them between 6 ft and 0.1 ft. You'll get the idea. The beam can be steered around 8 points of the compass rose. The beamwidth is wide enough to provide complete azimuth coverage at full gain. F/B is excellent! As for 40m, I've never tried that with parasitic GPs. I have built several vertical 40m yagis that employed vertical 1/2 wave elements that were supported by trees or overhead lines for really tough "new ones" with huge hungry pile-ups with excellent results in all cases. (Electromagnetics works -even for us "poor folks"!) The array that I've shared with you should be scalable to 40m. I've done that with EZNEC, but never built it. I don't have any real feel for parasitic arrays with buried radials, or "radials on the ground". I expect that such arrays might require some tricky tuning. BTW - in my experience, with elevated resonant radials, once we have 4 - we seem to be reaching a "point of diminishing returns" and increasing the number of resonant elevated radials doesn't seem to buy much! Anyway, good luck! I would expect that a 2-element 40m parasitic array, that has provision for switching the parasite between reflector and director tuning could be made to play pretty well! If you are 5m from the array, I would think that your measurements are pretty good except for elevation effects. Best regards, Charlie, K4OTV -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim GM Sent: Friday, June 07, 2013 12:14 PM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check I think your too close to tell, or just coupling into every thing around there. Knowing you I am sure you have done every thing right. Try calling CQ during day light hours and see what signal strengths the Reverse beacons give you. http://www.reversebeacon.net/main.php Problem with doing this is the beacons may not re-spot you until your off the air for say 15 minutes or shift frequency. I do not know how they really tick. -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
* Are your radials resonant? For the purposes that you are attempting, they need to be, in order to maintain the phase relationship between the driven element and the parasite. Actually there are three cases that work: 1.) Where a limited size system has radials are exactly resonant 2.) Where the system is reasonably large, and because of size, has minimal (almost no) reactance contribution 3.) The small or resonant system is "tuned" to compensate ground system reactance out All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Hi, Jim I'm most suspicious regarding your radial systems: * Are your radials resonant? For the purposes that you are attempting, they need to be, in order to maintain the phase relationship between the driven element and the parasite. * Are your radials elevated? * Do your radial systems overlap or pass close to each other?? You can have considerable unintended and competing coupling via the radials that can destroy the parasitic relationship between the driver and parasite. I am attaching and EZNEC file of a 5-element 80m array that I designed and built some years ago, for a friend, Jim, W4RS, when he was in Virginia. It was a wonderful "kick-ass" "knock-'em-dead" antenna for tough long-haul international DX paths and a real "pile-up buster"! If you have access to EZNEC you can have a look. It consists of a central GP with 4 parasites arranged around it in a square. Each of the parasites has a 6 ft shorted line of 450 ohm ladder line at the base. The inductance of the 6 ft shorted line tunes the parasite as a director. Then the shorted line can be shorted an inch or so from the attach point at the vertical element and the radials, to switch it to director tuning. The result is that in the diagonal directions the array basically operates as vertical 3-element 1/2 yagi. In the N/S/E/W directions it operates as two horizontally stacked 3-element 1/2 yagis that share a common driver. If you have access to EZNEC. Please examine how I handled the resonant radials. The central GP driver has 4 elevated resonant radials that extend outward past the parasites. The parasites each have two resonant elevated radials that are at right angles to one another and are led away from the center of the array to minimize the radial coupling. The result was a "killer" 80m DX array that was the envy of a few serious 80m DXer down here in our area. If you want to play the beam steering, go into the "Transmission Lines" menu in EZNEC and switch them between 6 ft and 0.1 ft. You'll get the idea. The beam can be steered around 8 points of the compass rose. The beamwidth is wide enough to provide complete azimuth coverage at full gain. F/B is excellent! As for 40m, I've never tried that with parasitic GPs. I have built several vertical 40m yagis that employed vertical 1/2 wave elements that were supported by trees or overhead lines for really tough "new ones" with huge hungry pile-ups with excellent results in all cases. (Electromagnetics works -even for us "poor folks"!) The array that I've shared with you should be scalable to 40m. I've done that with EZNEC, but never built it. I don't have any real feel for parasitic arrays with buried radials, or "radials on the ground". I expect that such arrays might require some tricky tuning. BTW - in my experience, with elevated resonant radials, once we have 4 - we seem to be reaching a "point of diminishing returns" and increasing the number of resonant elevated radials doesn't seem to buy much! Anyway, good luck! I would expect that a 2-element 40m parasitic array, that has provision for switching the parasite between reflector and director tuning could be made to play pretty well! If you are 5m from the array, I would think that your measurements are pretty good except for elevation effects. Best regards, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim GM Sent: Friday, June 07, 2013 12:14 PM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check I think your too close to tell, or just coupling into every thing around there. Knowing you I am sure you have done every thing right. Try calling CQ during day light hours and see what signal strengths the Reverse beacons give you. http://www.reversebeacon.net/main.php Problem with doing this is the beacons may not re-spot you until your off the air for say 15 minutes or shift frequency. I do not know how they really tick. -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
I think your too close to tell, or just coupling into every thing around there. I get good F/B on arrays I test, even within a wavelength or two. As long as the elements are reasonable length (under 1/2 wave) and spacing reasonable, the pattern should be formed up almost totally by somewhere around ten times the widest element spacing. With two elements and 1/4 wave spacing, that's just two-three wavelengths (80-120 meters) away. As a matter of fact, it is usually better to test at a closer distance than out at the fringe of groundwave. There must be some problem with the system. Perhaps inadequate radials, coupling from element to element through radials, or too much other stuff making the array not work. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
I think your too close to tell, or just coupling into every thing around there. Knowing you I am sure you have done every thing right. Try calling CQ during day light hours and see what signal strengths the Reverse beacons give you. http://www.reversebeacon.net/main.php Problem with doing this is the beacons may not re-spot you until your off the air for say 15 minutes or shift frequency. I do not know how they really tick. -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Jim, Equipment wise, is this reciprocal if you use the array for your receive measurements? Jim, KR9U -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim Brown Sent: Thursday, June 06, 2013 5:29 PM To: 'TopBand' Subject: Topband: My Turn For a Brain Pick - Sanity Check I'm building a simple 2-el vertical array for 40M, with one element driven against radials, and a passive reflector with an equal number of radials. NEC predicts 2.7 dBi over lousy ground at 15 degrees, with peak gain of 3.6 dBi at 25 degrees elevation, and F/B of about 8 dB. We've got this set up in W6GJB's pasture, roughly 5 miles S of me, with me centered on the main lobe, and I'm looking signal strength with my K3 reading relative dB (and with AGC turned off). Our signal is 35 dB above the noise level with Glen's KX3 at 3 watts. Terrain is hilly between us, and we have 16 radials on both elements. We're making three measurements -- with the array as designed, with the reflector shortened by 3 ft (which should make it director) but still connected to the radials, and with the reflector simply insulated from the radial plate. What I hope to see if the antenna has the predicted directivity is 3 dB difference between the designed array and the reflector floating, and 6-8 dB difference between the array as designed and reversed. What I see instead is the same signal strength for all three configurations within 0.2 dB. So the question is, why? A vertical plot in NEC shows the F/B at all elevation angles, all the way down to 1 degree and up to 80 degrees. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Hi Jim, Have you tried measuring the current in the parasitic when connected? 73, Greg, ZL3IX On 2013-06-07 09:29 a.m., Jim Brown wrote: I'm building a simple 2-el vertical array for 40M, with one element driven against radials, and a passive reflector with an equal number of radials. NEC predicts 2.7 dBi over lousy ground at 15 degrees, with peak gain of 3.6 dBi at 25 degrees elevation, and F/B of about 8 dB. We've got this set up in W6GJB's pasture, roughly 5 miles S of me, with me centered on the main lobe, and I'm looking signal strength with my K3 reading relative dB (and with AGC turned off). Our signal is 35 dB above the noise level with Glen's KX3 at 3 watts. Terrain is hilly between us, and we have 16 radials on both elements. We're making three measurements -- with the array as designed, with the reflector shortened by 3 ft (which should make it director) but still connected to the radials, and with the reflector simply insulated from the radial plate. What I hope to see if the antenna has the predicted directivity is 3 dB difference between the designed array and the reflector floating, and 6-8 dB difference between the array as designed and reversed. What I see instead is the same signal strength for all three configurations within 0.2 dB. So the question is, why? A vertical plot in NEC shows the F/B at all elevation angles, all the way down to 1 degree and up to 80 degrees. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
