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Need QUAD Expert for Spacing of elements

BJ radionut said:
Look at the diagram on page 20. The narrow spacing of .125wl actually has the Higher gain.
I may be missing something but to me, the wider spacing is more ease of impedance matching. The .200 to .25 wl spacing the impedance gets nearer to 50 ohms.
This said 6.5ft spacing is too wide for 11m for max gain.
CK/DB help me out, my calculation has peak gain with >5ft spacing. (?)
All the Best
Gary
Click to expand...

What did you use to calculate the spacing Gary? IIRC maximum gain occurs with wide spacing up to 0.25 wavelengths. At 11m that would be over 8 feet which is truly too wide considering a much shorter boom will be easier to manage and have only a fraction of a dB less gain. IRC most commercial quads had spacing in the range of 60-66 inches so you are not far off. Admittedly I have never build a quad for 11m other than assemble the old Hygain two element quad. My quad experience has been on 6m/2m/70cm.
 
I am feeding with 75 ohm coax, so do not need length to get a 50 ohm match. 5 feet does seem to be average commercial spacing (60" TO 63") Hoping to hear many ideas on this. Like I said, there seems to be many different measurements both commercially and in calculators. Most calculators, or the old rule of thumb .15/wl to .2/wl seem to give longer results l. A shorter boom will be easier to manage for sure. I even saw a commercial with a boom of only 38 inches, with no matching unit required, with 7.5 dbi gain. Everyone's opinion is welcomed , Feel free to weigh in. And yes I am not hung up on getting an extra 1/4 of a db. Hoping for a realistic 7 dbi , with as close to 75 ohm direct feed. Any tuning ideas welcomed. Should I tune driven loop , by itself first, or tune driven loop with the reflector in place Thanks for your thoughts guys, you always give me great ideas, to me this is the fun of antenna building , playing with all the compromise , learning , building, tuning, for me this is great fun, have built something like 7 antenna in less than a year, loops have got me hooked, they just work well here for local and dx, so a 2 el is the next logical progression in my loop making. I have 2 -full wave loops up, and they work stellar.
 
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CK and All: I had to find my reference book.
The book is Bill Orr's 1959 edition, All about Quad Antennas.
"At a spacing of approximately 1/8 wavelength, the parasitic element (reflector) provides an array gain of 5.7 decibels when adjusted for a maximum gain." " The gain curve is fairly constant for element spacing from 0.1 wl to 0.2 wl, with the peak of the curve falling near 0.12 wl spacing."
Calculation: 1005/27.200 = 34.95 ft.
34.95 ft. x 0.12wl spacing = 4.43 ft. ( 53.16 inches)
This would yield a radiation resistance of around 65 ohms, thus with spacing near 0.15wl radiation resistances nears 72 ohms.

The spacing curve for a 2 element array differs greatly, (it seems) from a multiple-element array (3 or more) where maximum gain vs, the pattern width is of greater consideration.
The best pattern width does occur at spacing greater than 0.25+wl on the array.
Looking at his figures best beam width plus best F/B ration occurs at roughly 0.50wl spacing.
Overall we are talking in micro-hairs with max gain of approximately 5.7dBd (at 0.12 spacing)
and decreasing to approximately 1 dB less nearing the 0.22 wl.
OK after all of that at 5-6:00 am in the morning and 3 cups of coffee.
I am toast, and ready for some radio fun on 6 meters scatter.o_O:rolleyes::ROFLMAO:
All the Best
Gary
 
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He also stated that a Direct fed of 50 ohms occurs near 0.08wl spacing.
Looking at CUBEX spacing of 59 inches and fed with a 75-ohm matching stub, by his calculation seems right. Their gain figures seem high, but without knowing their true length of the size of the reflector and driven elements, I guess that could be close.
More coffee needed!!!!:ROFLMAO:
All the Best
Gary
 
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Hello xm49north7 and all: I have built a few 2 element quads and modified a PDL-II quad antenna. I used 5 Ft and or 6 FT spacing for the home brew quads.

Also used 10 gauge wire for the loops not for power handling but the 10 gauge wire after market wire (Thermalized-Coated magnet wire) didn't stretch as the cheap 14 gauge wire supplied by the PDL-ll manufacture.

It would be a neat test to measure the different quad spacing and such on a calibrated analyzer, in field strength measurements to document the different spacing lengths and matching systems. Iam sure there is articles out there that show analytical (computer generated) charts of the different spacing as compared to gain and rejection. But true field strength testing and making polar plots is the way to go. Please let us know how it turns out for you.

Jay in the Great Mojave Desert
 
BJ radionut said:
The spacing curve for a 2 element array differs greatly, (it seems) from a multiple-element array (3 or more) where maximum gain vs, the pattern width is of greater consideration.
Click to expand...

Definitely the case. All too often people will look at the element spacing of a multi-element array and simply apply the reflector to driven element spacing and think it is good. Such is not the case. The spacing will be different because the additional elements affect the overall characteristics.
 
Shadetree Mechanic said:
When adjusting element spacing, the first thing I would look at is beam width and take off angle. High gain does no good if it makes a null at the angle that your dx is coming in at.
Click to expand...

Which I have been preaching for YEARS. Don't be concerned about where the lobe is and how much gain is in that lobe as much as where the nulls are and how deep those nulls are. A 30 dB deep null makes MUCH more of a difference than an extra dB or two of gain.
 
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Good stuff guys, thank, you all. I think some of the problem with online info is the fact tht many people take a multi element beam , and use those measurements , just nocking off the directors.
 
BJ radionut said:
CK and All: I had to find my reference book.
The book is Bill Orr's 1959 edition, All about Quad Antennas.
"At a spacing of approximately 1/8 wavelength, the parasitic element (reflector) provides an array gain of 5.7 decibels when adjusted for a maximum gain." " The gain curve is fairly constant for element spacing from 0.1 wl to 0.2 wl, with the peak of the curve falling near 0.12 wl spacing."
Calculation: 1005/27.200 = 34.95 ft.
34.95 ft. x 0.12wl spacing = 4.43 ft. ( 53.16 inches)
This would yield a radiation resistance of around 65 ohms, thus with spacing near 0.15wl radiation resistances nears 72 ohms.

The spacing curve for a 2 element array differs greatly, (it seems) from a multiple-element array (3 or more) where maximum gain vs, the pattern width is of greater consideration.
The best pattern width does occur at spacing greater than 0.25+wl on the array.
Looking at his figures best beam width plus best F/B ration occurs at roughly 0.50wl spacing.
Overall we are talking in micro-hairs with max gain of approximately 5.7dBd (at 0.12 spacing)
and decreasing to approximately 1 dB less nearing the 0.22 wl.
OK after all of that at 5-6:00 am in the morning and 3 cups of coffee.
I am toast, and ready for some radio fun on 6 meters scatter.o_O:rolleyes::ROFLMAO:
All the Best
Gary
Click to expand...
The .15 sounds like what I am after , So 6 feet 5 inches sounds like more than I need maybe cut my boom for 5 feet, 6 inches and tune from there.Thanks for your reply, good info.
 
Below are two models of the 2 meter Quad that BJ posted in his post #12 above. See his link that was produced by HamUniverse.com.

1. is in Free Space and one is over Eznec's idea of Real Average Earth.

2. is a Real Earth model, and is set at 1 wavelength above ground at 146 MHz. I did the model to the specs and got pretty close to their posted results.

I will scale this model to 27.205 Mhz, tweak it as necessary and post the dimensions.

I added the model in Free Space since the article shows us results in FS. I also posted the Real Earth antenna patterns showing both the forward gain and angle, plus the rejection noted at the reflector as negative gain and angle...for those who are interested in rejection.
 

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  • HamUniverse 2 meter 3 element Quad.pdf
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