QUAD ANTENNA CALCULATIONS

[unit_399]

I'm getting ready to upgrade my 2-element quad to 4 elements. I know that it's design frequency is in the CB band, but my question concerns amateurs and Cbers alike, so I posted it here.

When I designed the 2-element,I used the calculator on this site:
The Ultimate Guide to 11 Meter CB Antennas

The length of the driven element at 27.385 was given as 440.387 inches.

Today, I decided to try another calculator:
Quad Antenna Calculator

It gave me the length of the driven element at 27.385 as 430.991"( a difference of almost 10 inches !)

Then I tried the ARRL formula of 1008/ fmhz. This gives and answer of 441.701"
The ARRL formula leads me to believe that the "Ultimate Guide" calculations are correct, but I keep wondering if I'm missing something here. I've tried to figure out what other variables would affect the driven element length, but I can't come up with anything that would account for a 10 inch difference. I've concluded that the "quad antenna calculator" formula is flawed.
ANY comments will be appreciated. Thanx & 73s

- 399

 

[Robb]

IIRC that the diameter of the wire - and if it has insulation or not - will affect the tuned length.

 

[unit_399]

Both calculators spec'd #12 uninsulated wire.

 

[Beetle]

Just a guess, but one might be optimized for forward gain and the other for maximum F/B ratio. They'll never both occur with the same dimensions.

 

[Robb]

Just a guess, but one might be optimized for forward gain and the other for maximum F/B ratio. They'll never both occur with the same dimensions.

Which one is which; Beetle?

 

[Beetle]

Wouldn't know; that's what experimenting is all about.:drool:

 

[Robb]

Here are some thoughts, JJ.

Measure the length of the radiator on your beam and compare it to the results of both formulas.
One should be pretty close I'll bet. Bet that is also the dim that has the best forward gain too.

Regardless of the formula, making the 1st director 5% less than the radiator is, and then making the 2nd director 5% less than the 1st radiator should get the desired results IIRC.

 

[TonyV225]

This is where the nail biting and pulling out of one hair comes into play, Its like anything else each person may do things differently and thus getting different or strange results and unless its a complete description parts used ETC it turns into not so much a guessing game but an experimenting game with minor adjust ments ETC. Remembet that as mentioned above the diameter affects the overall readings or end results.

 

[unit_399]

Thanks for the input. I have a lot of electroninc experience, but my antenna knowledge is zip. When I built my 2-element quad, I used the calculator on the Ultimate Guide site, and the antenna resonated at the design freq with less than 1" trimming. I want to build the 4-element, get it in the air, and use it without a lot of tweaking and unnecessary BS, and I will probably use the UG figures for the other 2 elements. I was just surprised that there was such a difference between calculators.
Beetle or TonyV, do you have any idea how element spacing affects element length ? Or where I can find some info on this. I have no choice but to build my antennas, so knowledge is key for me. There are a lot of sites that tell how to build a 4-element quad, but without any technical explanation. The ARRL antenna book is ok, but doesn´t go into detail on anything. So, any and all help is appreciated.

- 399

 

[BJ radionut]

399: Good Day old friend!
The Quad calculations can be all over the map, and many go back to when feed-point impedance was 300 or 150 Ohms and matching stubs or Gamma Matches were used to match them for max gain...
Now! For what's it worth....somewhere I made some notes in Bill Orr's "Quad Manual"....Here's what I found...for Direct 50 Ohm feed
27.400Mhz....
Side length of Loop....290/F(Mhz)=10ft/7 inches
Spacing....116/F(Mhz)=3ft/6 3/4 inches(42.75 inches)....

Now Mr. Orr has these specs for 70 Ohm(using 72 Ohm matching stub)
Side....248/F(Mhz)=9ft/3 inches
Spacing....118/F(mhz)= 4ft/4 inches

With Reflector +5%....Director -5%....with increased bandwidth by further shorting additional directors +/- 1 or 2%

Do you remember your specs from your working 2 element?
I would think your most likely some where right between these numbers...
I have an old copy of his book(Bill's Quad Manual) plus the addition of one of his Eng. Handbook....
I might be able to "scan" a page or two...scanners built into printers are hard to deal with....(should have never got rid of my old "flatbed" scanner)....
Also not knowing where your wish to "Tune" the Quad...
These extra notes:
28.400....
Spacing: 3ft/5 1/2 inches....41.5 inches
Side: 10ft /2 1/2 inches.....
So there is my worthless help to your cause! Link is for construction to 10m from French Ham
All the Best
GL
BJ

https://docs.google.com/viewer?a=v&...HiKLpU&sig=AHIEtbREIBKQHS1umJFVZtNg8B5T8kapXg
See his specs...if you match his 10m settings X 104%(11M) those numbers I have are way long(he is using 75 Ohm Stub)...So guess I'll keep looking for something better...:blink:
BJ
http://www.signalengineering.com/ultimate/4_element_quad.html