Home |
Search |
Today's Posts |
#18
|
|||
|
|||
Coax + Ladder Line
Jim Lux wrote in
: .... Mythical properties are ascribed to ladder line, some of attributable to ARRL publications. Or, I think more properly, to statements in ARRL publications taken with a different set of underlying assumptions.. The ARRL has long published characteristics of "Generic ladder line" being #18 conductors spaced 1". They publish loss figures better than theoretical loss for the same size copper conductors in a vacuum (eg at 10MHz, about 0.27dB/100m vs 0.47dB/100m). The second factor is, I think, the notion that since one-way loss is relatively low on open wire lines, that it is safe to consider it *always* insignificant (irrespective of VSWR), then exagerate the point by talking about it being essentially lossless at extreme VSWR. I think that the best characterisation we have of ladder line is that of Wes, N7WS. Similar measurements at lower frequencies might well reveal whether the stranded copper clad steel versions have inadequate cladding depth for copper-like performance at low HF. For instance, ladder line between a tube amp output tank and a doublet is probably "reasonably" low loss in most common practical applications.. Perhaps a better concept is "acceptable loss" where acceptable is influence by the application. The compromises accepted for multiband operation might well include 3dB of line loss on the lowest band. .... Ham applications in any case are kind of an odd thing, efficiency-wise, since the limit is on RF power at the transmitter output connector. Pretty much every other user of RF power amplifiers sets the system measurement plane somewhere else.. in space (EIRP or ERP) or at the power source (power budgets). For instance, you can trade increased power consumption against lower feedline loss. Actually, interesting you mention that. I recently had cause to probe the meaning of the term "transmitter" in our (VK) regulatory framework. Whilst we are limited in transmitter power output, the meaning of transmitter is relevant. From our legislation: ===quote 8 Definitions of radio emission and transmitter (1) For the purposes of this Act, a radio emission is any emission of electromagnetic energy of frequencies less than 420 terahertz without continuous artificial guide, whether or not any person intended the emission to occur. (2) For the purposes of this Act, a transmitter is: (a) anything designed or intended for radio emission; or (b) any other thing, irrespective of its use or function or the purpose of its design, that is capable of radio emission. === end quote It could be argued that an "emission" exists beyond the antenna ("without continuous artificial guide"), and that everything up to an including the antenna could be captured as part of a "transmitter" as defined. Though there is a well understood ordinary meaning to the word "transmitter", the drafters of the legislation have provided a definition that should override any ordinary meaning in the context of that law. Perhaps we (VK) are entitled to apply our limit to radiated power! Owen |
Thread Tools | Search this Thread |
Display Modes | |
|
|