Re: Topband: Beverage Question
The way I looked at it was that the equivalent diameter would be a bit less than twice the diameter of the wires plus the spacing. According to the Mil Spec for WD-1A/TT is 0.84mm diameter per conductor spaced 0.84mm (or perhaps 0.72mm if just twice sheath diameter. That gives around 2.5mm. The effective diameter will be less than this but it helps that the two conductors are twisted together. Can't do the maths for that but I reckon around 2mm diameter or 12 AWG. The standard formula (see eg http://www.w0btu.com) gives around 470 ohms with 50mm spacing. My quick tests with a 40ft sample of line (changing termination resistance and measuring SWR using an antscope via a 75/450 ohm transformer) show that to be about right for 450 ohm line. Jeremy G3XDK/G4AQG On 20 Sep 2014, at 16:14, Carl wrote: > The way I understand is that you will be using the WD-1A as individual lines > with each having its wires connected in parallel. > > Id start by calculating the resultant wire gauge such as say two #24 in > parallel = a #21; I dont know what the fudge factor would be due to wire and > jacket insulations in determinining the 6" spaced line impedance. From what > Ive read that is too much spacing for best performance due to imbalancing > plus not being a bit twisted to cancel the imbalance as with ladderline and > conventional WD-1A useage. > > If the reason for change is poor strength and reliability then why not go > with parallel galvanized or aluminum fence wire and create some twisting > arrangement every 100' so. > > In the more conventional installation I calculated about 93 Ohms for the > WD-1A and use a 1:1 ratio for 75 Ohm coax; cant notice any deterioation > between that and using 50 Ohm coax with its own transformer. Both work fine > to 30M. > > Carl > KM1H > > > > >> I want to replace the 450 ohm ladder line for my two DXE 720 ft long >> bi-directional beverages with two lengths of WD-1/TT field telephone wire. >> The wires will be secured only at the ends, but will be suported along their >> length by ceramic insulators mounted on 4x4 posts spaced every 60 ft. The >> spacing between the parallel wires will be about six inches. Here are my >> quesetions: First, does anybody know what the likely impedance is of this >> configuration, or if not, how to measure it? Second, if I keep the DxE >> matching trnsformers used with the 450 ohm ladder line, will beverage >> performance be degraded noticeably with the new wures if, say, the impedance >> of the new line turns out to be 600 ohms or so? In other words, as a >> practical matter how important to performance (e.g., F/B ratio and >> low-noise) is it to make sure impedances are matched. >> >> >> >> Finally, a mechanical question. I want to have a pulley at one end of the >> parallel wires to equalize the tension in the wires. I've not been able to >> find a good pulley with a five or six inch diameter, except for nylon >> pulleys used for clotheslines. Do you think one of these could be used. >> There will be no motion of the pulley, since it is only used to equalize >> tension. The field telephone wire is rated at 200 lbs maximum tension, and >> I'm guessing the actual tension will be about half that. >> >> >> >> Thanks! >> >> Jim W8ZR >> >> _ >> Topband Reflector Archives - http://www.contesting.com/_topband >> >> >> - >> No virus found in this message. >> Checked by AVG - www.avg.com >> Version: 2014.0.4765 / Virus Database: 4025/8246 - Release Date: 09/20/14 >> > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: AlexLoop in South Lyon Michigan
Dear Group I know that there is an AlexLoop in the South Lyon MI area that is at someone’s contest station. I lost the contact information for the person who has the station. (deleted a folder in my email) If I remember correctly his name was Bruce. I want to attempt to contact him and ask to see the system. He offered to show it in the past but like I said I messed up on a delete button. I am pretty sure that he is part of this reflector which is part of the reason for this email Thanks for the bandwidth. Thanks Don ~73 Don KD8NNU 2014 Top Gun :-) -.- -.. ---.. -. -. ..- _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Beverage Question
I've just finished putting up a ~300m NE/SW reversible beverage at G4AQG using two pairs of paralleled WD1/TT wire for the feeder, spaced 50mm apart. I used nine 2.7m 3x3 posts with electric fence insulators on top. The posts are held in the ground with a metal fence post spike. The wire is secured to insulators at the far end and tensioned with two fencing wire tensioners at the feed end, using egg insulators just before the tensioners. One end post is guyed with fencing wire to a 4ft 5/8" earth stake via a wire tensioner and the other guyed to a convenient tree. There are two 4ft earth rods at each end. I've put about 25lb tension in each line (measured with a travel scale) and there's hardly any sag in the line and apparently no need for spacers to keep the lines apart. Hopefully wind and any ice loading will be within the 200lb breaking strain of the paralleled wire! The impedance of the line is about 470 ohms and common mode is around 390 ohms. Allowing for earth losses in the termination, I reckoned that a 1:1 reflection transformer was about right. For 75 ohm coax, I used transformers with 6+6:5 , 7:3 and 3+3 :6 turns ratio wound on fair-rite binocular cores and direction switched by relay. I checked line impedance and matching impedance with an Antscope analyser, all seems OK. The beverage works well up to 30m. There's good f/b from a nearby AM station on 1485kHz ( at least 15dB) but not had time to measure 160m performance yet. Jeremy G3XDK/G4AQG On 20 Sep 2014, at 15:06, Jim Garland wrote: > I want to replace the 450 ohm ladder line for my two DXE 720 ft long > bi-directional beverages with two lengths of WD-1/TT field telephone wire. > The wires will be secured only at the ends, but will be supported along their > length by ceramic insulators mounted on 4x4 posts spaced every 60 ft. The > spacing between the parallel wires will be about six inches. Here are my > quesetions: First, does anybody know what the likely impedance is of this > configuration, or if not, how to measure it? Second, if I keep the DxE > matching trnsformers used with the 450 ohm ladder line, will beverage > performance be degraded noticeably with the new wures if, say, the impedance > of the new line turns out to be 600 ohms or so? In other words, as a > practical matter how important to performance (e.g., F/B ratio and > low-noise) is it to make sure impedances are matched. > > > > Finally, a mechanical question. I want to have a pulley at one end of the > parallel wires to equalize the tension in the wires. I've not been able to > find a good pulley with a five or six inch diameter, except for nylon > pulleys used for clotheslines. Do you think one of these could be used. > There will be no motion of the pulley, since it is only used to equalize > tension. The field telephone wire is rated at 200 lbs maximum tension, and > I'm guessing the actual tension will be about half that. > > > > Thanks! > > Jim W8ZR > > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
