Re: Topband: The Idiot's Guide To Bi-Directional Two-Wire BeverageConstruction...
Hi Guys, Many thanks to one & all for sharing your ideas & experiences with the two-wire bi-directional Beverage antenna with me...it's quite obvious that there's a wealth of know-how and experience out there in such matters. The jury is still out here re. the antenna's adoption into VE3CUI - VE3XZ: I already have a 1500' south-terminated Beverage, 50% (or more) of which crosses over some very wet, low-lying marshy land in my "back 40" (including a pond). I guess because of the "good" ground afforded by this reality, the Beverage can't hold a candle to my K9AY loop when temperatures are above freezing...but when ambient air is below 32F for more than a couple of days, the Beverage here starts to come into its own. If I was to try a bi-directional two-wire affair, I'd want to keep it the minimum recommended length---and that would mean that its entire run would have wet soil beneath it... Oh well, as the saying goes, you can't have enough antennas for 160...and even if the system was useable only on those below-freezing days, it might still be a worthwhile project to undertake, such that my ability to copy the "JA" stations might be enhanced (the whole reason as to why I'm even thinking of this)... ~73~ de Eddy VE3CUI - VE3XZ ___ Topband reflector - topband@contesting.com
Re: Topband: The Idiot's Guide To Bi-Directional Two-Wire BeverageConstruction...
Which is why military telephone wire as well as old rural Copperweld pairs are so popular;pacing is a constant and self twisting during installation is a given. Calculated self impedance agrees well with results and a properly constructed set of transformers with minimum C coupling give the best F/R and common mode isolation. They do exhibit a velocity factor so you cant make one as long as a single or wider spaced pair of wires. With my very poor ground conductivity rain or seasonal variations seem to have little or no effect, 2-3 ground rods and 25-30' radials establish the reference. Carl - Original Message - From: "Mike Waters" To: "topband" Sent: Thursday, December 13, 2012 5:05 PM Subject: Re: Topband: The Idiot's Guide To Bi-Directional Two-Wire BeverageConstruction... What we have is a transmission line that carries the signal from one direction. If the spacing between the wires varies, then the impedance does. In that case, the F/B ratio can suffer. The Z ratio of the transformers at each end depends upon this impedance. http://www.w0btu.com/Beverage_antennas.html#How_far_apart 73, Mike www. On Thu, Dec 13, 2012 at 3:08 PM, Eddy Swynar wrote: I wonder if I might prevail upon any & all with some first-hand real-world experience as to the "criticalness" (if any) between the two wires running the length & span of a 2-wire bi-directional Beverage...? Just how important is a continuos pre-set distance between the wires, anyway...? And who was it that came up with the necessity of equally-spaced wire...? And how did they determine the "optimum" distance the wires...? ___ Topband reflector - topband@contesting.com - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1430 / Virus Database: 2634/5456 - Release Date: 12/13/12 ___ Topband reflector - topband@contesting.com
Re: Topband: The Idiot's Guide To Bi-Directional Two-Wire BeverageConstruction...
Just how important is a continuos pre-set distance between the wires, anyway...? And who was it that came up with the necessity of equally-spaced wire...? And how did they determine the "optimum" distance the wires...? Would a span of power line cord (a.k.a. "zip cord") do in a pinch...? Eddy, The transmission line mode of the two wires is what brings the far end of the antenna to the feedpoint. That is what allows the antenna to be reversed. If that line is lossy, or if that line is mismatched by just 2.5:1 SWR and the wrong length, the antenna can easily lose 20 dB of null depth when in the forward (fires away from feedpoint) direction. In the reverse direction, where the antenna fires toward the feedpoint direction, mismatch or loss only affects signal level. SWR or loss does not affect F/B in the "reverse" directional mode. You can use any impedance of line you desire if transformers are readjusted to the correct ratio, and you can even use coaxial cable for the antenna. The problem comes in when the line has greatly unstable impedance, velocity factor, and/or loss, and the major problem is mostly in one direction. I'd avoid exceptionally lossy lines and lines that significantly change characteristics with weather conditions. It is easier to make good transformers when impedance ratio of antenna mode to transmission line mode is close to unity. That's why 400-600 ohm line spacings are usually best. 73 Tom ___ Topband reflector - topband@contesting.com
