tmsmp%Ucb-Vax@homxb.UUCP (05/12/85)
I am interested in building a directional antenna to replace my trap vertical. The ARRL Antenna book contains plans for a log-periodic dipole array. This caught my attention as an alternative to stacked monoband beams. I have obtained the original QST article (Nov. 1973) and will try to contact the author. Does anyone have any experience with or knowledge of this type of antenna? Does any commercial manufacturer offer one? If not, why is there no commercial interest? Is there a fatal flaw in the design? The QST article states that the author uses a transmatch to "eliminate possible harmonic radiation caused by the frequency-independent nature of the array." Is interference a major consideration? Any help is greatly appreciated. Thanks Tom Swift KD2MF (formerly WA2JEH) AT&T Information Systems Holmdel homxb!tmsmp 201-949-3374 (W) or 201-577-6945 (H)
YOUNG@DEC-MARLBORO (05/13/85)
I think KLM offers a log periodic or two. The "problem" with log periodics is that they trade gain for bandwidth. A properly designed monoband yagi will have better gain than a multi-band log periodic. From numbers that I've seen, a tribander will give more gain for a given boom length than a log periodic (these were manufacturers gain figures, not to be taken too seriously). The only advantage I can come up with for the log periodic is that it will cover the WARC bands. Log periodics also have disadvantages in that all the elements must be insulated from the boom, split, and fed. I would go with the monobanders, or a good tribander before I would go to a log periodic. Paul Young, K1XM --------