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Gonzo
Intermediate Member
Username: Gonzo
Post Number: 118
Registered: 9-2004
| | Posted on Monday, November 29, 2004 - 6:48 pm: | 
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I am sure this will be un-popular, but here goes anyway. Keep in mind your "S" meter is calibrated anywhere between 4-6 db's per "S" unit. I have found that this also varies quite a bit,depending upon whether someone is doing a 1 "S" unit or a 9 "S" unit.The "S" meter almost always appears looser on the low side (1 on the meter) versus the high side (9 on the meter). Of course different radios can have completely different ressults. Ok so here goes:
ANTENNA GAIN TABLE
Design of Antenna DBI gain DBD gain Type of antenna Makes & Models
# elements per side (Beam)
Isotropic radiator 0 -2 Omni Directional Imaginary antenna
1/4 wave ground plane 0.2 -1.8 Omni Directional 9 foot high vertical , 4 radials
1/2 wave Dipole 2 0 Omni Directional A-99, Big Stick,Ringo, Starduster,Maco Alpha
3/4 + 7/8 J-pole designs 3.4 1.4 Omni Directional Avanti Sigma 4, Sirio Vector 4000,
5/8 wave Vertical 3.4 1.4 Omni Directional Imax2000,Hygain Penetrator, Devant
2 element V-Quad 7 5 Beam Maco V-Quad, Jo Gunn skip Jack
2 element Yagi 7 5 Beam Cushcraft,Lafayette
Super Scanner 2 / 7.2 0 / 5.2 Omni & Beam Super Scanner
2 element Quagi 8 6 Beam Y-Quad
2 element Quad 9 7 Beam PDL II, Super Hawk, Magnum-2cb
3 element Yagi 10 8 Beam Maco 103C,Spit Fire, Jo Gunn 3+3,WY3,MB-11
3 element Quagi 11 9 Beam Maco Comet,
3 element Quad 12 10 Beam
4 element Yagi 12 10 Beam Maco 104C,Jo Gunn 4+4,WY4,A-411S.
4 element Quagi 13 11 Beam Moonraker 4, Shooting Star,
4 element Quad 14 12 Beam SE. White Lightning, Magnum-4cb
5 element Yagi 14 12 Beam Maco 105C,Jo Gunn 5+5,WY5,A-511S.
5 element Quagi 15 13 Beam
6 element Yagi 15 13 , Maco 106 C,Jo Gunn 6+6,WY6
6 element Quagi 15 13 Beam Laser 400,
6 element Quad 16 14 Beam Lightning 6+, Magnum-6cb
7 element Yagi 16 14 Beam Maco 107C,WY7
8 element Yagi/Quagi 17 15 Beam Maco 108C, Super Laser 500,Jo Gunn 8+8
8 element Quad 18 16 Beam Lightning 8+
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Gonzo
Intermediate Member
Username: Gonzo
Post Number: 120
Registered: 9-2004
| | Posted on Monday, November 29, 2004 - 10:37 pm: |
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I see this didn't post very well, so I will try and make sense of one line:
2 element Quad 9 7 Beam PDL II, Super Hawk, Magnum-2cb
This means: 2 element Quad antenna
next number 9 = db gain against isotropic
next number 7 = db gain against dipole
next is antenna type: Beam
next is various advertised antennas fitting description |
Tech833
Moderator
Username: Tech833
Post Number: 899
Registered: 8-2002
| | Posted on Tuesday, November 30, 2004 - 10:16 am: |
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Gonzo,
Well...
You should be applauded for your effort. Some of your antenna grouping is incorrect. |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 122
Registered: 9-2004
| | Posted on Tuesday, November 30, 2004 - 4:05 pm: |
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Yes, I was trying to generalize. Some other things: Long boom antennas will give you about a 1 db gain more than a comparable number of elements in a short boom antenna. So some of the grouping is not quite exact. The results tested above are certainly more accurate than advertised manufacturers inflated figures. |
Bruce
Senior Member
Username: Bruce
Post Number: 1826
Registered: 9-2003
| | Posted on Tuesday, November 30, 2004 - 10:43 pm: |
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Hummmmm?
Maby im miss reading but Using DBD ....
Gain in DBD for a 3 elm yagi is around 6.5 ( call it 7)
SO if you go to 6 elm it would be 10 dbd , and 12 elm about 13 DBD. To get 16 DBD you would have to go 24 elm and the boom would have to be 3 waves long or about 100 foot.
How did you get the gain numbers ? are you using ground reflections to add to the gain?
Bruce
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Gonzo
Intermediate Member
Username: Gonzo
Post Number: 124
Registered: 9-2004
| | Posted on Wednesday, December 01, 2004 - 12:30 pm: |
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Maybe you are Bruce: I think you are trying to say that if you double the amount of elements you get 3db gain? 3ele = 7 6ele= 10
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This is not true, especially with larger arrays
If you double the amount of elements this does not mean that you get 3db gain. There is a sliding scale as to what additional elements give as far as gain, with diminishing results after about 5 elements.
Yagi example: Going from a dipole (1 element) to 2 elements gives about 5 db gain. this is rated against DBD gain as you stated.
1ele dipole = 0 db gain
1ele to 2ele = 5 db additional gain (1 reflector)
2ele to 3ele = 2-3 db additional gain(1 director)
3ele to 4ele = 1-2 db additional gain
4ele to 5ele = 1-2 db additional gain
5ele to 6ele = 1 db additional gain
6ele to 7ele = .5-1 db additional gain
7ele and up = .5 and less depending upon boom length.
After about 3 elements Boom lenght becomes somewhat of a stronger db influencer than the total number of elements. So the numbers mentioned above can vary somewhat.
How far out on the boom the last director is, is what focuses the main radiation lobe...not how many directors there are in between.
If you had a 20 element yagi and pulled out 3 directors in the middle of the boom,(every other director) you wouldn't even hardly notice the difference. The table I put up, is geared towards the long Boom lenghts. And I am being very generous with the gain figures. Some of the grouping as Tech883 mentioned is not entirely accurate, but was shown for simplicity's sake.
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And there IS a difference how Yagi's perform in relation to frequency. a 6 element Yagi on HF/CB frequency is quite a performer, where as on UHF and higher,it is nothing to write home about.
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I actually thought most of the discussion would be how these figures are TOO LOW, in comparison to manufacturer's figures. Which I have found to always be inflated.
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Bruce
Senior Member
Username: Bruce
Post Number: 1828
Registered: 9-2003
| | Posted on Wednesday, December 01, 2004 - 3:45 pm: |
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What? gain is not doubled by doubling the number of elements? ONLY for the first 3.
AFTER the FIRST 3 elements gain is fairly LINEAR now IF CORECTLY designed there should be VERY LITTLE to NO change in gain from 3 to 500 mhz if ......
1) the elements are corectly decoupled from the boom
2) The spacing and total wave lengh are the same.
Gain of a Yagi-Uda array IS dependant on boom lengh in wave lenghs but also when you double the number of elements the gain will increase by about 3 db..... also based on using .15 to .25 spacing ( average for most antennas ) you will find that the total boom lengh is about double.
NBS / LARSON and others found no real change in gain as to frequency now a 3 elm 900 mhz antenna would not look too hot while a 27 mhz one would ONLY because the 900 mhz ant boom is about 6 inches and the cb one is 9 foot so it makes no sence to make a 900 mhz ant THAT SMALL. Capture area is smaller and losses are higher but good design will take care of most of that.
Again a 6 elm beam will produce about 10 DBD of gain to get to 16 you will have to make the boom 4 times as long and with evenly spaced elements that works out to 24. NOT TO SAY YOU CANT WIDE SPACE AND DROP A FEW.
Your sliding scale of gain Hummm ....look at your own numbers 3 elms gives 7 to 8 DBD and go to 6 and your own numbers show 3-5 db more ( 5 is way high )
Yagi - UDA more that 50 years ago layed the ground work for these antennas THEY ARE NAMED AFTER THEM and there numbers have been provin over all that time ..... NOT THAT A BIT MORE OF GAIN CANT BE SQUEEZED OUT IT CAN but not 3,4, or 5 db better in a average array.
unless you have discovered something very new its the old addage you cant get something for nothing and a yagi os only a way of focusing your signal and nothing else...... check out Larson and NBS papers on yagis good stuff. |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 127
Registered: 9-2004
| | Posted on Wednesday, December 01, 2004 - 9:49 pm: |
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Listen Bruce you are entitled like everyone else to your own opinion. I have found like many others (William Orr W6SAI, Stuart Cowan W2LX, Paul Lee N6PL, George Brown M5ACN,etc.etc.) That there is a law of diminishing returns. But in reality your numbers and mine are not very far off. Just at the beginning.
Since going from a 6 element beam to a 12 element beam. Each additional element would provide very little gain, until you got to 12 elements and then you would have about 3 db additional gain...all from 6 additional elements. We both agree this is true. Each additional element only providing about .5 db
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On the lower end:
A 6 element yagi beam , gives more than 3db gain over a 3 element yagi. Just ask anyone who has tried both. The boom length itself contributes to the gain as do the elements in this case. 3 element cb beams sold by antenna manufacturers have a 10-11 foot boom, and a 6 Maco element beam (just as an example) has a 31 foot BOOM!! A 20 foot difference!! This plus the 3 additional elements gives more than 3db gain. Again not as much as manufacturers would have you believe but more than 3 db. |
Bruce
Senior Member
Username: Bruce
Post Number: 1830
Registered: 9-2003
| | Posted on Thursday, December 02, 2004 - 7:38 am: |
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Yagi's law
You double the array size you increase gain by 3 DB. Run the numbers on that 6 elm maco using 12 elems ..... 3 db more. This law applys for many directors out on to the boom. At CB over 3 or 4 gets too big but on bands like 440 10-25 elm beams are commonly used with gains per yagi in the 15-18 DBD range.
I would like you to send me that 8 elm quads E and H plans for 16 DBD gain. to get that gain your E and H lobes would have to be less 30 deg each and a boom of about 4 waves long ( 150 foot). You dont know how much i would like to build a antenna of that kind of gain using only 8 elms 4 of them would be more than enough for moonbounce. My last moonbounce array was 4 stacked 19 elm klms and they had about 20 dbd gain. |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 129
Registered: 9-2004
| | Posted on Thursday, December 02, 2004 - 10:59 am: |
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As far as the other point: "there is no real change in gain as to frequency"
Remember the conversation we had about capture area? And how YOU said that it is important at VHF & UHF frequencys. You are absolutely correct. AND this is also the reason why a 6 element beam on cb that has a 31 foot boom, with 6 18 foot elements on it....has more gain than a UHF beam that is 6 elements and 2foot long.
Capture area usually refers to recieving capabilities, but it applies to transmitting gain as well. This is why at UHF frequencys more elements are needed to get the same amount of gain. Or else everyone would be happy carrying around 6 element UHF beams that have 2ft long booms. This is why on 440 mhz you need 20 element beams.
Can you imagine having a 3 element 440 mhz beam? with one foot elements? on a 1foot beam??
However a 3element correct sized Cb band beam is certainly a worthwhile investment in time and money, as the 1000's of 3 element cb beam owners will tell you.
Try telling 440 mhz owners that they only need 3 element beams about 1ft long, and you will quickly have your email box flamed with all kinds of obscenitys. |
Bruce
Senior Member
Username: Bruce
Post Number: 1831
Registered: 9-2003
| | Posted on Thursday, December 02, 2004 - 12:35 pm: |
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Gonzo
What are you talking about capture area or gain?
"AND this is also the reason why a 6 element beam on cb that has a 31 foot boom, with 6 18 foot elements on it....has more gain than a UHF beam that is 6 elements and 2foot long"
WHAT? ..... never seen this either ...
"This is why at UHF frequencys more elements are needed to get the same amount of gain. "
Where did you get that? If so how did they do the measurments. Now TRUE some poorly designed antennas will have some what less gain but it will be trivial.
The fact is ........
Gain will be the SAME but the capture area of a CB antenna will be MANY times that of a 440 antenna. The REASON for large arrays on 440 are as follows
1) YOU CAN DO IT EASLY
2) CAPTURE AREA IS VITAL ON UHF AND A LARGE ARRAY HAS MORE OF IT.
3) ALL signal losses are higher at 440 so making it up with a large antenna just makes good sence.
Background noises on bands above 2 meters drop off quickly and you can take advangage of this a 20 db gain antenna to go get the weak ones while on cb you might get rid of lots of junk but the main lobe will be hammered with noise.
Run the numbers on that 8 elm moonbounce quad since 4 of them will do the job nicely 4 will give me 22DBD gain but 4 of the 14 elm hygain 16 foot boom yagis will only give me 20. |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 130
Registered: 9-2004
| | Posted on Thursday, December 02, 2004 - 4:52 pm: |
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"CAPTURE AREA IS VITAL ON UHF"
"ALL signal losses are higher at 440 so making it up with a large antenna just makes good sence"
I agree with what you are saying, I think we are arguing over symantecs. However I believe as do others that gain does vary with frequency. You disagree...thats fine.
Maybe I am unable to express myself properly by typing that could be.
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So we don't get off topic,
Here is the main point:
If you have a 3 element cb beam and purchase a 6 element 31 ft boom beam, you will go up more than 1/2 "S" unit.
A 6 element CB beam with a 31 foot boom has more than 3db gain (1/2 a "S" unit) than a 3 element cb beam with a 10 foot boom. This is what the table shows.
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Bruce
Senior Member
Username: Bruce
Post Number: 1832
Registered: 9-2003
| | Posted on Thursday, December 02, 2004 - 8:32 pm: |
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Capture area IS NOT GAIN. It DOES increase with gain. Now lets see that 8 elm quad run for 27 and 144 mhz ......THAT would be intresting to see what your program puts out. I would also like to see a 8 elm yagi ( same boom lenght ) it should be about 2 db less. |
Gonzo
Intermediate Member
Username: Gonzo
Post Number: 131
Registered: 9-2004
| | Posted on Thursday, December 02, 2004 - 9:11 pm: |
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Yes we are in agreement.
I did send you the specs on the 8 ele quad
And I believe a 8 ele yagi would be about 1-2 db less gain than a 8 ele quad |
Bruce
Senior Member
Username: Bruce
Post Number: 1833
Registered: 9-2003
| | Posted on Friday, December 03, 2004 - 5:10 am: |
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e-mail wa4gch@yahoo.com
There are REAL world limits to Yagis a 136KHZ antenna would have to be up 1/2 mile just to avoid being detuned and a 10GHZ antenna would become a nightmare even rain would detune it.
I have used them as high as 1296 MHZ with great results the last one was 32 elms and worked fine.
For years i ran stacked 9's on 220 mhz untill hurricane Alina got them in 85.
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