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Analog Angle

My Antenna Dilemma: Preamp or Passive?

Bill Schweber
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Ranasinghe
Ranasinghe
6/30/2013 11:48:12 PM
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Master
Re: wrong size for frequency?
True Brad, It is a wasting of time to repair the antenna. 

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Brad Albing
Brad Albing
6/25/2013 11:45:36 AM
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Re: A vs B
@Bill - Me too regarding the mysterious magic. More complicated than a dipole with no reflector or director elements around it - else I'm lost.

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Brad Albing
Brad Albing
6/25/2013 11:42:49 AM
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Re: A vs B
@eafpres - I'll try the λ/2 spacing and see what happens.

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eafpres1
eafpres1
6/24/2013 10:10:44 PM
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Re: A vs B
The best spacing is 1/2 wavelength at the center frequency.  A simple way to consider this is to first think about wavefronts leaving the antenna heading towards the reflector, and ones leaving the antenna in the opposite direction.  If the spacing is 1/2 lambda, then the reflected waves arrive in phase with the waves going the other way, and have constructive interference, increasing the gain.

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Bill_Jaffa
Bill_Jaffa
6/24/2013 5:12:22 PM
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Re: A vs B
Re #1: I'd have to refresh my memory, starting with the ARRL Antenna Handbook (lots of practical information there); undoubedly it is some sort of phasing thing. (Antennas and arrays always seemed like a lot of mysterious magic to me, frankly.) But some of today's EM field-analyis tools can do an amazing job of modeling and assessing antenna performance--hello, anyone out there willing to model this?

Re #2: I assume it's worth starting with a lambda/4 spacing. The nice thing about this design it that it is easy try various postions and adjust and try again. And since it is indoors, there is no need to climb on the roof, and the elements and reflector don;t hav to be heavy-duty materials!

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Brad Albing
Brad Albing
6/24/2013 5:02:03 PM
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Re: A vs B
I did track down more info than I could shake a stick at regarding those V-array configurations. Oddly, none of the descriptions I read spoke to these two issues of interest:

1. In a 4-array, why is polarity swapped on the top and bottom antenna sections, but the middle two are operated in phase?

2. In some versions, a reflector is placed behind the array (behind being arbitrary - there is no behind until you put a reflector there). No one states what the spacing should be between the reflector and the array elements.

Does anyone here know?

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Brad Albing
Brad Albing
6/24/2013 4:55:13 PM
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Re: wrong size for frequency?
Finally checked this myself - looks like pretty much nothing on the VHF low-band now.

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Brad Albing
Brad Albing
6/14/2013 11:12:06 AM
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Re: The antenna system choices.
OK - Bill, I await further reporting on your research regarding the co-linear antenna array. Otherwise, I'll be forced to do my own experimenting.

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Bill_Jaffa
Bill_Jaffa
6/13/2013 10:40:42 PM
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Re: The antenna system choices.
I agree--and it would be lowest cost and most fun to "experiment" with. Sure, quality low-loss coax is more expensive that junky coax, but it would be a good idea to use it regardless of whether I go active or passive--so that is not a cost difference in one versus the other,

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WKetel
WKetel
6/13/2013 10:34:22 PM
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Artist
The antenna system choices.
A simple set of fabricated co-linear antennas like the one described in the link would be a good choice for in the attic, followed by the best low-loss balun available, and connected with a very good grade of low loss coaxial cable, would provide the best compromise. No amplifier to die or go into oscillation, no wall wart to waste power and then fail, and a typical time between failures in the tens of years, or better if it is kept out of harms way.

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