| Author |
Message |
    
Ozfisho
New member
Username: Ozfisho
Post Number: 2
Registered: 4-2012
| | Posted on Sunday, April 29, 2012 - 5:27 am: | 
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Hi again all, I've started building a monster quad antenna that I've seen in in the AARL antenna handbook, probably from around 1998 I guess. But anyway, how do I set up the SWR if it's out a bit after I build it?
73's and
Cheers
Dale
Busselton
West Australia |
Tech833
Moderator
Username: Tech833
Post Number: 2160
Registered: 8-2002
| | Posted on Monday, April 30, 2012 - 12:17 pm: |
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A monster quad for which band? Assuming it is truly a monster, I am guessing 80m or 40m?
Tuning all depends on how the quad is fed. Give us some more details, please.
Your radio 'Mythbuster' since 1998
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Ozfisho
New member
Username: Ozfisho
Post Number: 4
Registered: 4-2012
| | Posted on Tuesday, May 01, 2012 - 8:02 am: |
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Howdy Tech guy, this one is for 11m for the CB
Cheers
Dale
Busso
WA |
Tech833
Moderator
Username: Tech833
Post Number: 2161
Registered: 8-2002
| | Posted on Sunday, May 06, 2012 - 10:02 pm: |
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OK, well you certainly don't need a "monster quad" to do 11m. Lucky for you, 11m only needs about 36 feet circumference +/- loops.
Make the directors a little smaller than 36 feet, make reflector a little bigger. Doubling the number of elements adds 3 dB of gain. So, to get 3 dB more gain than a 3 element, you need a 6 element. To get 3 dB more gain than a 4 element, you need an 8 element, etc.
In numbers, say your 3 element quad has 11 dB gain. a 6 element quad will have about 14 dB gain.
The trick to making a quad work well is feeding it properly, and element spacing. About 1/8 to 1/4 wavelength between elements seems to work best. Less than 1/8 spacing, and the pattern gets ugly and you lose gain and efficiency. More than 1/4 wave spacing messes up the front to back ratio. Quads are not much like a yagi when it comes to spacing and tuning, but a quad will have more gain than a yagi with the same number of elements.
Your radio 'Mythbuster' since 1998
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Ozfisho
New member
Username: Ozfisho
Post Number: 5
Registered: 4-2012
| | Posted on Thursday, May 10, 2012 - 10:54 pm: |
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Hi Tech guy, I'm looking at a 4 element quad, got all the spacings from above mentioned ARRL handbook that broke the spacings down for each HF band, so hopefully what they have for 11m id ok to work with, hate to build, push it all up into the air and then find it's not going to perform.
Regards
Dale |
Henry_hpsd
Junior Member
Username: Henry_hpsd
Post Number: 12
Registered: 2-2007
| | Posted on Thursday, May 10, 2012 - 3:19 pm: |
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Hello,
Just a small correction:
It is not the number of elements that "double" the gain...
It is primarily boomlength that takes care of gain.
If one doubles the boomlength you roughly add about 2.7 dB.
http://www.copperelectronics.com/cgi-bin/discus4/discus.cgi
Kind regards,
Henry 19SD348
www.dx-antennas.com |
Tech237
Moderator
Username: Tech237
Post Number: 1573
Registered: 4-2004
| | Posted on Friday, May 11, 2012 - 9:38 am: |
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Henry - Doubling the elements WILL double the gain. A perfect example of this is stacking yagis. Added a second Yagi, correectlty spaced and phased DOES add 3bd to the gain of a signel yagi.
By the way the ARRL Antenna Handbook, along with multiple other sources all verify that doyubleing the number of elements on a common boom will also double the gain.
if you have access to NEC or any other Antenna Modeling program, set up a three element yagi on a given size boom, then doubel the boom size without adding elements and watch the gain actually drop.Now using the large boom, add the extra elements, and the gain will double (or close to) that of the original 3 element yagi.
Tech237
N7AUS
God made me an athiest, who are you to question his wisdom?
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Henry_hpsd
Junior Member
Username: Henry_hpsd
Post Number: 13
Registered: 2-2007
| | Posted on Sunday, May 13, 2012 - 4:15 am: |
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Hello,
With your permission, please allow me to change your opinion.
You have made 3 statements and we will investigate them a bit futher.
1- A second yagi will indeed profide about 3dB gain (depending on distance). But do you also notice besides the "extra" elements, you have doubled the boom length.
2- The ARRL antenna handbook.
well perhaps you have an older copy? as there have been (and still are) some mistakes in the ARRL antenna handbook.
on the subject boom length reference gain mine tells another story:
Let me quote: (11-4 chapter 11 Yagi performance Optimization pragraph "gain and boom length"
Start:
As pointed out earlier, the gain of a Yagi is largely a function of the length of the boom. As the boom is made longer the maximum gain potetial rises. For a given boom length the numer of elements populating that boom can be varied, while still maintaining the antenna's gain.
End of quote ARRL antenna handbook.
No need for me to futher explain the above.
3- Yes i do have acess to NEC, infact i earn a living using NEC 2, 4 and other MOM's etc. I have costructed antennas for the Military in Afghanistan and am a HF antenna propagation instructor. Not that i know all, by far..but i do know what your talking about.
Of course a 3el where you just "double" boom length will show a dramatical drop in gain. One can not just "double" the boom length without futher optimalisation.
If your statment was accurate it would also mean that by deviding your original boomlength (doing the opposite) while keeping the number of elements the same the gain wouldnt drop....but it does.. doesnt it ?
I hope the information provided has given another point of view.
Kind regards,
Henry HPSD |
Ozfisho
New member
Username: Ozfisho
Post Number: 8
Registered: 4-2012
| | Posted on Sunday, May 27, 2012 - 1:58 am: |
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Howdy all, quad antenna is coming along nicely. 4.74M x 50mm x 50mm aluminium square tubing for boom. I've just acquired some bamboo poles, quite straight at around 6ft each. Would these be ok for being the spreaders for each element? I'll weather proof them somehow before using them if they will be ok to use.
73's
Cheers
Dale
Busselton
Western Australia |
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