Gary, this is part semantics, part my error. I can agree with your statement. My original statement was that getting significantly off frequency with a parallel-fed colinear array would result in less gain at the horizon and more at "unhelpful angles."
Looking back at some of my models, I can see that even in the two-element arrays, the main lobe may get fairly distorted, but remains perpendicular to the array as long as they're fed in phase. This is not the same as tilt. The ones that began tilting were things like 5/8 spacing with phasing 45 degrees off, etc. Guys, thanks for making me look more closely. 73, Paul, AE4KR ----- Original Message ----- From: Gary Glaenzer To: [email protected] Sent: Sunday, June 08, 2008 6:53 AM Subject: Re: [Repeater-Builder] Re: antenna suggestions for 440mhz Paul; If the elements continue to be fed in-phase, the main lobe cannot shift up or down It may, however, become narrower or wider, causing a gain or loss of signal at some point below the perpendicular-to-the-plane-of-the-elements line at a distance, thus giving an APPARENT shift up or down Regards, Gary ----- Original Message ----- From: Paul Plack To: [email protected] Sent: Saturday, June 07, 2008 7:18 PM Subject: Re: [Repeater-Builder] Re: antenna suggestions for 440mhz "No, parallel-fed antennas do NOT suffer uptilt/downtilt as frequency is varied unless the harness was special-ordered for factory downtilt. If the antenna wasn't ordered with downtilt, all of the elements are fed in phase, and they will always be in phase regardless of frequency." Jeff, the pattern depends on both phasing and spacing. As frequency drops, the interelement phasing, expressed in degrees, remains the same, but the spacing, expressed in degrees or wavelengths, drops. If you model a colinear array of parallel-fed dipoles in an antenna software program, and don't scale the dimensions as you scale the frequency, you'll see the main lobe shift up or down, and "butterfly" lobes appear, as you get a few per cent off-frequency. In an extreme case, a pair of vertical colinear dipoles fed in phase with half-wave spacing has the familiar big lobe toward the horizon. As frequency rises, the pattern degrades until, at a frequency of 2X, it becomes an end-fire array, with most energy directed straight up and down. This happens with no change in phasing or spacing. 73, Paul, AE4KR
