Re: Topband: [Bulk] Top Loading wires
T hanks for the correction, Stan. My old eyes missed that!! A 90' tower won't require much top-loading at all! Sorry for my error 73, Charlie, K4OTV -Original Message- From: Stan Stockton [mailto:wa5...@gmail.com] Sent: Wednesday, February 04, 2015 1:41 PM To: Charlie Cunningham Subject: Re: Topband: [Bulk] Top Loading wires It's a 90 foot tower he is describing. Sent from my iPad On Feb 4, 2015, at 12:11 PM, Charlie Cunningham charlie-cunning...@nc.rr.com wrote: Gee, I surely agree with Grant, Larry! I've used EZNEC for MANY years, with great results, and I've designed, built, tested and measured many wonderful EZNEC designs - including some really complex killer antennas! I do think that 28' top loading wires will be WAY TOO SHORT atop 50 ft. of Rohn 25! More like 50-70' will be needed to resonate that tower. You will probably do just as well with TWO top-loading wires in a Tee configuration! The point is for the top-loading wires to extend the tower to 1/4 wave resonance on 160. Of course you could make an excellent 80m antenna with the 50' tower and some modest top-loading wires approaching the length that you are considering. GL! If you are going to be experimenting with low-band antennas, EZNEC is a GREAT investment 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Grant Saviers Sent: Wednesday, February 04, 2015 11:28 AM To: Larry - K1UO; Topband Reflector Subject: Re: Topband: [Bulk] Top Loading wires With an insulated tower, the cheapest EZNEC and other free NECs will yield good results. Would you rather climb, cut, and trim a few times or spend $89 to get EZNEC? Simple to learn. And the demo version is free eznec.com Grant KZ1W no affiliation, just a long term happy user On 2/4/2015 7:27 AM, Larry - K1UO wrote: Could someone tell me the length of top loading wires (4 wires planned) needed to add to the top of a base insulated 90 foot Rohn 25g tower to maximize the radiation resistance on 160 meters. I understand there is a point of diminishing returns on the top loading lengths. The 4 wire angles will be around 45 degrees or as close as possible.If I knew how to model ,or even had a modeling program, I would attempt this already relatively simple task to many. From 50+ years of practical experience, I am ‘guessing’ maybe 28 feet long each? _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: [Bulk] Top Loading wires
On 2/4/2015 7:27 AM, Larry - K1UO wrote: Could someone tell me the length of top loading wires (4 wires planned) needed to add to the top of a base insulated 90 foot Rohn 25g tower to maximize the radiation resistance on 160 meters. I understand there is a point of diminishing returns on the top loading lengths. The 4 wire angles will be around 45 degrees or as close as possible.If I knew how to model ,or even had a modeling program, I would attempt this already relatively simple task to many. From 50+ years of practical experience, I am guessing¹ maybe 28 feet long each? I just modeled a 90 ft tower with a flat T top of #12 that varies from 28 ft to 60 ft from center. A total of 30, 1/4 wave radials are buried six inches. I¹m using 4Nec2 with NEC v4.2. This is not your planned set-up, but it serves as an illustration. With 28 ft. flat-top spokes, the current distribution is still highest at the ground. By the time you get to 50 ft. spokes, current maximum is just under the center of the vertical (~ 30 ft.). With 60 ft. spokes, current peaks in the middle of the tower. Maybe as a compromise, 40 - 50ft would be reasonable. Current is still strong over the entire length of the vertical radiator but maximum is lifted up away from the ground. With a 60+60 =120 ft. total length flat hat, you¹re going to find resonance is way down in the AM broadcast band (about 1410 kHz in this example). But so what? Forget the frequency of resonance and pay more attention to current distribution. On 160m, a simple L network network at the base will get us 50+j0. Paul, W9AC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: [Bulk] Top Loading wires
The tower is 90 feet, not 50 feet. On Wednesday, February 4, 2015 12:11 PM, Charlie Cunningham charlie-cunning...@nc.rr.com wrote: Gee, I surely agree with Grant, Larry! I've used EZNEC for MANY years, with great results, and I've designed, built, tested and measured many wonderful EZNEC designs - including some really complex killer antennas! I do think that 28' top loading wires will be WAY TOO SHORT atop 50 ft. of Rohn 25! More like 50-70' will be needed to resonate that tower. You will probably do just as well with TWO top-loading wires in a Tee configuration! The point is for the top-loading wires to extend the tower to 1/4 wave resonance on 160. Of course you could make an excellent 80m antenna with the 50' tower and some modest top-loading wires approaching the length that you are considering. GL! If you are going to be experimenting with low-band antennas, EZNEC is a GREAT investment 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Grant Saviers Sent: Wednesday, February 04, 2015 11:28 AM To: Larry - K1UO; Topband Reflector Subject: Re: Topband: [Bulk] Top Loading wires With an insulated tower, the cheapest EZNEC and other free NECs will yield good results. Would you rather climb, cut, and trim a few times or spend $89 to get EZNEC? Simple to learn. And the demo version is free eznec.com Grant KZ1W no affiliation, just a long term happy user On 2/4/2015 7:27 AM, Larry - K1UO wrote: Could someone tell me the length of top loading wires (4 wires planned) needed to add to the top of a base insulated 90 foot Rohn 25g tower to maximize the radiation resistance on 160 meters. I understand there is a point of diminishing returns on the top loading lengths. The 4 wire angles will be around 45 degrees or as close as possible.If I knew how to model ,or even had a modeling program, I would attempt this already relatively simple task to many. From 50+ years of practical experience, I am ‘guessing’ maybe 28 feet long each? _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: [Bulk] Top Loading wires
On Wed,2/4/2015 10:52 AM, Paul Christensen wrote: On 160m, a simple L network network at the base will get us 50+j0. For about 7 years, I've tuned my Tee vertical well below the band (by making the top loading wires longer), raising the drive point impedance to 50 + jX Ohms. The antenna looks inductive, so it's simple to add series capacitance to tune out jX, and you end up with a nice match. As noted, this moves the peak of the current up a bit. BUT -- don't forget that it will also change the current distribution along the length of the radials, which CAN increase loss in the radials. N6BV (retired ARRL Antenna Book editor) has NEC4, and modeled this for me with the radials. He said that from a radiation point of view, there was no benefit to moving the current up the tower, but it didn't hurt either, so the tuning method doesn't hurt antenna efficiency. Until about a month ago, the vertical section was 86 ft, with about 130 ft horizontal (Tee). My tree climber, who is also an arborist, told me that the big Madrone tree that held up one end of the Tee was dead and in danger of falling on my water tanks, and that we should take it down. He did, and found a young Douglas Fir, about 120 ft, to move the antenna to. He did, and I ended up with 100 ft vertical. I now have about 82 ft horizontal, and it tunes with about 900 pF. I modeled the antenna in EZNEC, and dimensions came out within a foot or so from what I measured. SWR Bandwidth of an antenna is increased by making the conductors larger, and for quite a while, I've used two parallel lengths of #10 THHN spaced about 10 inches. Both versions (old and new) are giving me better than 1.8:1 up to about 1910 kHz. Prior to lengthening the top section, I measured feedpoint Z of 33.8 ohms at resonance, about 1710 kHz. I've got about 60 radials laying on the ground, varying in length between about 67 ft and about 130 ft, and the soil here is quite poor -- very rocky, mountainous. Looking at a graph in the ARRL Antenna Book for radiation resistance vs vertical height, I'd guess that I have about 10 ohms of resistance in the radial system. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: [Bulk] Top Loading wires
On Wed,2/4/2015 11:09 AM, Charlie Cunningham wrote: T hanks for the correction, Stan. My old eyes missed that!! A 90' tower won't require much top-loading at all! Especially by the time you consider 1) it's diameter and 2) the aluminum on top that is bonded to the mast 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
