40883644
Premium
join:2003-06-05
Parker, CO
2 edits | My putty analogy
After seeing the omni vs. sector comparison come up again, I have decided to share my putty explanation
My putty analogy
An omni and sector antenna comparison is easy to explain, but you must understand a few characteristics of antennas.
1. Antennas do not create RF, they only shape it
2. A properly manufactured and installed antenna should not consume much RF or reflect it back to the radio if the VSWR (Voltage Standing Wave Ratio) is kept to 1.2:1 to 1.5:1 by the manufacturer
An omni antenna
Imagine or ”just do it”… A ball of soft putty about the size of a baseball is a good size.
Form the putty into a nicely shaped ball, lay it down and poke your finger into the center until you touch whatever’s at the bottom. What you have done is created a somewhat doughnut shape. Taller then a doughnut and rounder then a doughnut but starts to take on the shape. Let’s call this a 1dBi radiation pattern.
Now start to flatten the ball until it is half as high but twice the diameter. You now have a 4dBi radiation pattern.
Flatten the ball again until it is half as high as the previous and again twice the diameter. You have now created a 7dBi radiation pattern.
Every time you flatten the ball to half the height and double the diameter you increase the gain by 3dBi
If you continue to do this 3 more times you create a 16dBi radiation pattern and what you’ll have in front of you is a very flat but very large diameter putty disc.
As you noticed, the height decreased as the diameter increased which is exactly what your ability to reach customers will do. You can now reach out further but may start to overlook close customers due to the thinner pattern.
A sector antenna
Right where you left off, you can now make a sector antenna.
Fold the flat putty disc over like a perfect omelet, and now what you have created is an 8dBi 180 degree sector pattern. You have not changed the distance it will travel in one direction but you have doubled your vertical height.
Now flatten the omelet shaped putty until it reaches out twice as far and is half as high but still retains the 180 degree / omelet shape. You have just doubled your gain.
Fold the putty now into a quarter round shape by folding it sideways. This creates a 90 degree sector pattern that has the same capable distance but the vertical coverage has doubled again.
Disclaimer
This should help explain RF shaping differences between omni antennas and sector antennas. I use it when talking to my customers and hope it doesn’t insult anyone’s intelligence
To keep the explanation simple I have not brought into the mix what side lobes, front to back ratios, down tilt etc are. If this makes some sense, you can go on to study what that’s all about some other time.
Rich
»www.highgainantennas.com |
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PersComp
Premium
join:2005-08-17
Cayce, SC
| ***I didn't see this thread until after I had posted in the other one, so I copied it here as it fits better.***
Excellent method of illustrating!!! I thought I had the antenna concept ironed out (flattened doughnut, etc), but this makes me think a little deeper.....and tell me if I am thinking correctly.
So as you created the 8 dBi 180 sector and then flattened it , the gain returned to 16dBi. However since the coverage distance did not reduce when the putty was folded in half, the 16 dBi sector has the potential to cover MUCH more area than the 16dBi omni (not a true doubling, but probably 20-30% further).
I guess I just thought that 16dBi was 16dBi and was only concerned with additional interference when using an omni vs a sector. But, your illustration tells me that not all antenna gain is created equal!!! |
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uscomputing
join:2005-01-26
Buffalo, NY
| reply to 40883644
Great post, Rich.
Unfortunatly my hands smell like play-doh now!!
Oh well:
»home.businesswire.com/portal/sit···sLang=en |
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AnonName
@12.160.x.x | reply to 40883644
Excellent analogy, Rich. Well explained.
-m- |
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rfnut
Premium
join:2002-04-27
Fisher, IL
 ·Mediacom
| reply to 40883644
Very nice analogy.
BTW.
VSWR is Voltage Standing Wave Ratio.
When a transmission line is terminated with an impedance, that is not equal to the characteristic impedance of the transmission line, not all of the incident power is absorbed by the termination. Part of the power is reflected back so that phase addition and subtraction of the incident and reflected waves creates a voltage standing wave pattern on the transmission line. |
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rawgerz
In Debt we trust
Premium
join:2004-10-03
Grove City, PA
 ·Verizon Online DSL
 ·Sprint Mobile Broa..
| reply to 40883644
I was bored so I tried some photoshop
I think that's how it should be? |
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40883644
Premium
join:2003-06-05
Parker, CO
1 edit | rawgers
Nice, it even looks like putty 
I took your art and doubled the RF from 100mW to 200mW to help answer inova's question. 
rich
»www.highgainantennas.com |
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inova
join:2006-05-03
Macnutt, SK | reply to rawgerz
Nice photoshopping! Can you take one of those pics and demonstrate the effect of varying the power applied? |
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rawgerz
In Debt we trust
Premium
join:2004-10-03
Grove City, PA
·Verizon Online DSL
·Sprint Mobile Broa..
1 edit | I can't imagine the outcome of that, highgain's examples were easy to follow. But judging from RM examples I've done I'd say going from 50-250mw would give you 25-30% better dBm's in a given area, so you might see 55dBm in a spot that was previously 64 with 50mW.
--
"Hows your French toast?" "Smelly and ungrateful, but this AMERICAN toast is great!" |
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Airplane777
join:2004-06-20 | reply to 40883644
Hi Rich:
Very good practical explanation. |
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rawgerz
In Debt we trust
Premium
join:2004-10-03
Grove City, PA
·Verizon Online DSL
·Sprint Mobile Broa..
3 edits | reply to 40883644
Sectors with about 10* down tilt. The towers and antennas aren't even close to scale I'm sure haha
I never did CAD so mine are basically a shot in the dark 
Haha, Rich using my image when your site says 'sorry our images are copyrighted' I see how it is Just kidding
--
"Hows your French toast?" "Smelly and ungrateful, but this AMERICAN toast is great!" |
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Airplane777
join:2004-06-20
2 edits | Rawgerz:
Really neat sector illustrations. |
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AnonDOG
@12.160.x.x
| reply to 40883644
Rich;
I debated mentioning this but your analogy is SO good that I think I should.
A 3 dB increase is worth 1.414 times as much distance. A 6 dB increase is worth 2.0 times distance. Clearly you know this, and I have forgotten it many times; but as I said, your example is just SO good that this deserves mention.
-m- |
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thewildthang
join:2005-12-21
Winfield, AL
| reply to 40883644
Good example Rich, one that I can finally use in mixed company(as if this has ever been a topic of discussion in mixed company). An old radio man once explained it to me as: when a bull walks across the highway and makes a deposit, that is as a unity gain antenna, if a vw bug comes along and runs over it that makes it as a 3 db gain antenna, but if an 18 wheeler comes along and runs over it that makes it as a 9 db gain antenna. In all cases you have the same amount of crap, it's just spread wider and thinner with the higher the gain. |
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kewlkeed
Grouch
Premium
join:2005-02-05
Knowlton, QC | reply to 40883644
I vote for Sticky on this thread 
Very good explanation. |
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superdog
I Need A Drink
Premium,MVM
join:2001-07-13
Lebanon, PA
| said by kewlkeed  :I vote for Sticky on this thread Very good explanation. I agree. The problem though, is that we already have quite a few stickies up there, and if we add to many, it will push all of the newest relevant threads to a second page??, Maybe??
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korym
Go Wisp's
ExMod 1999-03
join:1999-12-23
Richmond, VA
clubs:
| said by superdog :I agree. The problem though, is that we already have quite a few stickies up there, and if we add to many, it will push all of the newest relevant threads to a second page??, Maybe?? Well, FWIW, I posted it to Start a WISP, with full credit to Rich, of course, specifically at:
»www.startawisp.com/content/view/417/53/
In fact, I'm starting to put useful posts there strictly for organization purposes. Radialink mentioned recently a bunch of lightning arrestor threads. I've posted some of them there too.
And, (I don't want to hijack the thread, of course, but since it came up...), I'm almost done with the Wiki site as well.
Hope this helps.
Regards,
Kory
--
WISP Directory : WISP News : Start a WISP |
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