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Author Topic: mono band stacking sideways ?  (Read 1480 times)
N4JTE
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« on: May 25, 2012, 09:22:56 AM »

I am considering running two 40 meter wire beams in an end to end configuration at relatively same height and obviously the same direction. The plan is to get as much end to end seperation as feasable and feed with 1/4wl or 3/4wl, 75 ohm to each beam and Y connect to main feedline. Is it reasonable to expect an increase in gain and a possible narrowing of the effective beamwidth ?
Tnx
Bob
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KD8GEH
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« Reply #1 on: May 25, 2012, 10:01:17 AM »

Is this a trick question Bob?  Grin

Sorry I missed you at Hamvention, next year.

73, Dave KD8GEH
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N4JTE
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« Reply #2 on: May 25, 2012, 02:42:37 PM »

Nope not a trick question, was hoping someone might have some experience doing this.
Have the room for a while to experiment so there you go, hi
bob
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WB6BYU
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« Reply #3 on: May 25, 2012, 03:55:32 PM »

You get colinear gain just the same as adding half wave dipoles in a line, or
a Extended Double Zepp (except that you can place them further apart.)
In fact, what you are proposing is the same as stacking vertically polarized
VHF beams one above the other.

Seems to me there was an article in one of the ARRL Antenna Compendiums on
someone who did this using beams on separate towers, with the ability to feed
them though different lengths of coax so he could rotate them and still keep
them in phase.

Putting them side-by-side as you propose gives more gain and narrows the
pattern.
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N4JTE
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« Reply #4 on: May 25, 2012, 04:19:51 PM »

BYU, tnx so much, not sure if I will proceed as the single two element reversable has an amazing beamwidth which I don't want to lose just to be louder, hi.
Appreciate your thoughts always.
Tnx
Bob
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K4SAV
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« Reply #5 on: May 25, 2012, 04:21:50 PM »

Here is some info on stacking antennas either vertically or horizontally. 
http://www.w8ji.com/stacking_broadside_collinear.htm
For horizontal stacking look at the graph labeled "Collinear Gain".  You can see that for antenna separation of 1 wavelength, the max you can get is about 3.25 dB more than a single dipole.   The graph is for free space but there won't be much difference over real ground when compared to a dipole at the same height.   You will have to subtract the coax loss and that could be significant since the antennas are so widely separated.  You will probably have 119 ft of coax going to each antenna before you can tie them together.

Of course the pattern is different from that of a single dipole.  At low angles the pattern splits into 4 lobes / 4 nulls or maybe 6 lobes / 6 nulls and at higher elevations it changes to 2 lobes / 2 nulls.

Jerry, K4SAV
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K5LXP
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« Reply #6 on: May 25, 2012, 04:25:39 PM »

Putting them side-by-side as you propose gives more gain and narrows the pattern.

I thought that the attribute of phased antennas vs more elements was that you got gain without changing the pattern?  In this scenario, the antennas will have "as much end to end seperation as feasable".  Therefore the patterns should be identical, with a net increase of ~3dB.


Mark K5LXP
Albuquerque, NM
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N4JTE
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« Reply #7 on: May 25, 2012, 04:33:49 PM »

Mark and Jerry, that's my constraint, the end seperation on the two reversable beams will end up a fraction of a WL, at best maybe 30 ft between the two antennas, worried about interaction and degradation of pattern etc, BUT, will probaly try it out anyway, too much free time, hi.
Tnx to all.
Bob
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WB6BYU
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« Reply #8 on: May 25, 2012, 05:01:59 PM »

Quote from: K5LXP

I thought that the attribute of phased antennas vs more elements was that you got gain without changing the pattern?  In this scenario, the antennas will have "as much end to end seperation as feasable".  Therefore the patterns should be identical, with a net increase of ~3dB.



I'd be surprised if you get any gain without also changing the pattern - gain and directivity
are interrelated.

A half wave doublet for 80m is two half waves in phase on 40m, and has about 2dB gain over
a dipole, with a narrower pattern.  Using two yagis, I'd expect to see about the same increase
in gain, though I'd have to model it to see if there was much interaction.  If you add about 1/4
wave spacing between the driven elements, it is just like using an Extended Double Zepp for
the driven elements with separate directors and reflectors on each end:  here is W4RNL's
article on the EDZ beam, including the resulting pattern:

http://www.cebik.com/content/edz/edz.html
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K4SAV
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« Reply #9 on: May 26, 2012, 06:40:59 AM »

Mark and Jerry, that's my constraint, the end seperation on the two reversable beams will end up a fraction of a WL, at best maybe 30 ft between the two antennas, worried about interaction and degradation of pattern etc, BUT, will probaly try it out anyway, too much free time, hi.
Tnx to all.
Bob

With these dipoles arranged end-to-end, they aren't "reversible beams".  They have a fixed bi-directional pattern.  You could change the pattern by changing the phasing between the dipoles to something other than zero degrees.

With only 30 ft between the ends of the dipoles, and with the dipoles at 50 ft, max gain over one dipole is about 2.7 dB.  That doesn't include coax loss, which will be higher for the phased dipoles.  That occurs in only two directions and at a narrow beamwidth.  For example, at 15 degrees elevation the phased dipoles have more gain than a single dipole over a total of 78 degrees.  For the other 282 degrees, the single dipole has a lot more gain (3 to 35 dB more).  That 35 dB number happens because of the nulls that develop in the phased dipoles pattern, which aren't there with a single dipole.

Jerry, K4SAV
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N4JTE
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« Reply #10 on: May 26, 2012, 12:15:48 PM »

Jerry, both pairs of dipoles are already independantly reversable using christman phasing of 84 degree feed with 71 degree phase line for change of direction. They will be fed with 3/4 wl, 75 ohm line and joined with tee conector to main 213 feedline to shack. Hoping the side to side arraingment will possibly double ERP and front to back, already substantial with single beam.
tnx for comments,
Bob
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K4SAV
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« Reply #11 on: May 26, 2012, 05:13:17 PM »

Oh, it was unclear that you were stacking 2 element arrays horizontally.  Everyone thought you were stacking single dipoles.

You can do that and maybe pick up something between 2 and 3 dB, but it will be at the expense of narrower beamwidth.  Still it might be a useful antenna if you have it pointed at a good direction, like central Europe.

Jerry, K4SAV
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N4JTE
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Posts: 1154




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« Reply #12 on: May 26, 2012, 08:55:28 PM »

Yepper Jerry did not did not ask it correctly, hard to condense this type of question but gonna do it after i get another 200 ft of rg8x, and went out and figured it will be 1/2 wl apart, should be interesting, tnx for your thoughts, you are always on point!
Bob
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