Need QUAD Expert for Spacing of elements

[xm49north7]

Ok, I am building a 2 element quad for 11 meters. I have checked many building plans, and many online calculators. None of them agree. For the spacing between driven element and reflector, I get everything from 3 feet to 5 feet to 8 feet, I get a number saying 62 inches and 63 inches, 67 inches. Some say longer the better for gain ,I would welcome any experience, thoughts, modeling info. I have most of my parts made, just deciding on boom length to start with, more interested in gain, than front to back, as where I live in rural area, there is no back traffic at all. Majority of my contacts are in a south to west zone. Thank you in advance, for those who wish to jot down there thoughts. I am using 27.200 mhz for my calculations (channel 20) Also this will be a quagy design, my loops are aprox. 6 feet wide by 12 feet tall, made from #14 stranded copper wire and driven is middle side fed, for vertical polarization. This will be top hung from a wood boom, On a wood pole. at 30 feet to the top boom to start .

 

[Road Squawker]

Ok, I am building a 2 element quad for 11 meters. I have checked many building plans, and many online calculators. None of them agree. For the spacing between director and reflector, ... edit... .

Well, there's your problem,.......... a 2 element quad doesn't have a director and a reflector.

 

[xm49north7]

I worded that wrong, thank you; it has been corrected to say driven and reflector

 

[Captain Kilowatt]

A quad is fairly forgiving for element spacing. Gain will vary very slightly with reasonable changes in spacing. Mmost of the time spacing can be varied to obtain a better match without compromising gain much at all. Look at the spacing 9f a commercial quad and copy it. They already did the math to the n'th degree on it.

 

[xm49north7]

But why such big difs, even in manufactured quads, anywhere from 3 feet to 8 feet?? for 2 el quad. 5 feet seems to be the most common. I am think of starting at around 6 feet 5 inch, spacing.

 

[Unit 75]

The longer the spacing the more forward gain at a loss of back rejection. Shorter spacing has better rejection with a loss in forward gain which explains the spacing.

 

[BJ radionut]

http://www.cubexquads.com/CB.htm
MAGNUM-2CB 11 Meter 2 Element Quad

• 9+ dBi gain @ 40 FT.; F/B >23dB
• 1 MHz Bandwidth - 2:1 VSWR
• Rugged fiberglass spreader arm construction
• 1.75" Aluminum Boom, 59" long
• 1/4w 75 ohm Matching Section included
• All-weather construction
• Handles full Legal Limit Power
• Small size, big performance; weighs just 26 lbs.
• Turning radius - 7.2 ft
• "Diamond" configuration

 

[BJ radionut]

http://on5au.be/Cebic/Cubical-Quad-Vol-1.pdf

 

[Alan Blackmon]

BJ that was a great read. I have yet to actually build a quad. I tried decades ago and it just didn't work out for me. I didn't know about feeding it properly then so my SWR was crazy bad. Now I just don't see how I could get a pass on it with my wife. Thinking though a quad at 2 meters would be fun.

 

[xm49north7]

http://on5au.be/Cebic/Cubical-Quad-Vol-1.pdf

Yes Cebik is great have both his books, I will just build with the 6 feet 5 inch boom and tune from there.

 

[Captain Kilowatt]

But why such big difs, even in manufactured quads, anywhere from 3 feet to 8 feet?? for 2 el quad. 5 feet seems to be the most common. I am think of starting at around 6 feet 5 inch, spacing.

It depends on what factor is optimized. You can only optimize one at the expense or the other two and they are bandwidth, forward gain, or front/back ratio. Some maunfacturers like to try and make short booms attractive to people with limited space so they develop a short boom which would require slightly different element lengths. In all honesty I cannot even imaging an 11m quad with a 3 foot boom. That is only about half of optimal spacing.

 

[BJ radionut]

http://www.hamuniverse.com/3el2meterquad.html

Here you go ALAN: 19" TALL and Less than 3 ft. Long and Direct Feed with about 7 dB gain over a dipole for 2 meters!
Small enough to Stack a pair!
All the Best
Gary

 

[xm49north7]

It depends on what factor is optimized. You can only optimize one at the expense or the other two and they are bandwidth, forward gain, or front/back ratio. Some maunfacturers like to try and make short booms attractive to people with limited space so they develop a short boom which would require slightly different element lengths. In all honesty I cannot even imaging an 11m quad with a 3 foot boom. That is only about half of optimal spacing.

All about the forward gain for me, do not really care about front to back, as there is almost zero local here, and no real noise sources at all, I am many miles from any town. So 6'5" sounds like the plan

 

[BJ radionut]

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

 

[Captain Kilowatt]

All about the forward gain for me, do not really care about front to back, as there is almost zero local here, and no real noise sources at all, I am many miles from any town. So 6'5" sounds like the plan

The 0.1 or 0.2 dB difference is nothing. You will lose more in the coax cable. People tend to get all worked up over a fraction of a dB yet it takes a full 6 dB to make 1 S-unit difference in signal strength.