Phasing 2 LPA's

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zguy1243

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I have been toying with the idea of co phasing 2 DPD 225-400Mhz LPA's. I understand the gain would be about 3 DB by doing this. I also understand that the antennas must be separated by 1/4 wavelength. Should it be a 1/4 wavelength at the lowest operating frequency or the highest? The low being 225 and the high being 400. Also do the antennas need to be separated horizontally or vertically on the mast? Does it matter? Also some insight on the phasing harness would be good too. Looking for alot of info here.


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Jody
 

prcguy

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There is a way to phase two LPAs and the high frequency parts will be close together and the low freq parts will be farther apart. It will resemble two antennas looking cross eyed in the same basic direction. The goal is to have the spacing the same fraction of a wavelength for all frequencies. I don't know that the spacing will be and you will need a broad band 50ohm splitter with equal length 50ohm cables to each LPA. The cable length should not be critical except to keep them the same.
prcguy
I have been toying with the idea of co phasing 2 DPD 225-400Mhz LPA's. I understand the gain would be about 3 DB by doing this. I also understand that the antennas must be separated by 1/4 wavelength. Should it be a 1/4 wavelength at the lowest operating frequency or the highest? The low being 225 and the high being 400. Also do the antennas need to be separated horizontally or vertically on the mast? Does it matter? Also some insight on the phasing harness would be good too. Looking for alot of info here.


Thanks
Jody
 

zz0468

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Kinda sounds like a can of worms to me. The theoretical gain is 3 db, but that doesn't take into account the loss of the phasing cable and the splitter/combiner. Reality is, it'll probably be closer to 2 db, which in my book would make it not worth it.

I've seen TV antennas resembling the cross-eyed thing prcguy mentions, and the antennas are stacked one above the other and horizontally polarized. In your case, you'd want them vertically polarized, which would make them side by side.
 

K4NRG

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If you already had the 2 antennas it could be a fun experiment. But you have to take into account the phasing lines are usually odd multiples of 1/4 wavelength at the operating frequency. For a single, narrow, bandwidth antenna it's usually pretty easy. For a broadband antenna I could see where that could be a challenge to find the magic lengths that would work best.
 

prcguy

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That's why you would use a broad band 50ohm divider and equal lengths of 50ohm cable in this case.
prcguy
If you already had the 2 antennas it could be a fun experiment. But you have to take into account the phasing lines are usually odd multiples of 1/4 wavelength at the operating frequency. For a single, narrow, bandwidth antenna it's usually pretty easy. For a broadband antenna I could see where that could be a challenge to find the magic lengths that would work best.
 

kb2vxa

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Guys, to keep it SIMPLE phasing can only be accomplished at one frequency or a VERY narrow band segment. Any departure and you have a Frankenstein lash-up where everything goes haywire so there goes that idea right out the window.
 

af5rn

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Guys, to keep it SIMPLE phasing can only be accomplished at one frequency or a VERY narrow band segment. Any departure and you have a Frankenstein lash-up where everything goes haywire so there goes that idea right out the window.
LOL! That sums it up with a pretty cool visual! :lol:
 
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