Antenna Difference

10-16-2001

Sup guys

I'm kinda new around "stumblin" the wireless community, so I got some question.

What is the diff between parabolic antenna and a yagi?
I thought both are for long distance, but what's the diff?

and also, is the diff between parabolic 19db and 24 db big?
'coz the price diff is so big....

thats all 4 now....thanx in advance

10-16-2001

The difference between a yagi and a parabolic dish?

A yagi is a series of elements one reflector, one driver (this is the only element that has the feed line hooked to it), and one or more directors. The more elements there are the higher the gain and the tighter the beam.

A parabolic dish is just that a concave saucer like collector and a feed horn that is hooked to the feed line.

The diffence between 19Db and 24Db is 5Db. You have to make the desicion to pay the extra money or not. What are you trying to accomplish?

Later,
D

10-16-2001

If you go with the parabolic you will be more than doubling your gain across the freq range; every 3 dB step doubles your gain... so the para has more than twice as much gain as the Yagi. Is this for point-to-point or portable? if this is for p2p your front-to-back ratio with the Yagi will be crap...

Just my 2 centavos

chris

10-17-2001

Chris,

Are you saying side by side that a 19DBd Para compared to a 19DBd Yagi is twice as good?

Can you explain more for us that don't quite understand why the Para would outperform in such a huge way?

Thanks.

10-17-2001

Hi again,

I'm going to use it to connect my laptop with my cable modem connection at home.
My campus is about 7 miles, blocked by trees and apartments.
I figured that if I bought either a yagi or a para,
I could point it to my campus so I can go wireless
there.
I think i prefer the 24Dbi one, and yes it's for point-to-point.

You said that if I use a yagi, front to back will be crap.
Isn't it supposed to be side to side? 'Coz a yagi is a directional antenna, so the front has the best range of coverage. Or mebbe i'm wrong, please correct me.

Anyway, still cant decide to buy a yagi or a para.
any suggestion welcomed.

Thanx.

10-17-2001

The dB scale is <ahem> a LOGARITHMIC PROGRESSIVE SCALE... (man that's fancy) as opposed to a linear scale, it's like the Richter scale in that every step forward in the scale is a multiple of the previous number. Every 3 dB higher is actually double the energy/signal, every 10 dB is 10 times, 20 dB is a 100 times the signal strength, so on and so on. When an isotropic point source is radiating 360 deg. in free-space it exhibits 0 gain... so when you see " x# dBi" it's in reference to a number a certain multiple times above that. I'm more used to "dBd" which uses a single dipole as a reference point. The difference in dBi vs. dBd is, uhm, 2.14 or something close to that; 5 dBi = 3 dBd. SO ANYWAY... the difference in gain values between 19 dB and 24 dB is 5 dB, so roughly 2.6 times as more signal strength. Sorry this is so long, but this is what I do for a living.
'Cheers

Chris

10-17-2001

Hey I just re-read this thread and I missed a point, I thought the original post was a question comparision between a 19dBd Yagi and a 24 dBd para... RATS.
Ok so two different antenna designs which have the same gain will both be operating with (very roughly) the same power level. Sort of.

Front-to-back ratio; the ration of signal at the peak gain point (0 degrees) as compared to the back (180 degrees), though a truer comparison would be from peak gain @ 0 deg. to everything from 90 deg. to -90 deg. the whole 180 degrees behind the antenna. A good FTB number is -25 to -30 dB down from peak gain; it's no big deal except in interference with users on the same frequency nearby; your signal could be picked up in the opposite direction thereby defeating the purpose of a directional antenna in the first place.

10-17-2001

Take a Yaggie and use it as the horn of a parabolic! Let me see...18dbd Yaggie + 24dbd Parabolic = 42dbd! Freaking awesome! LOL

That is assuming that dbd simply adds together and all the dbd of a parabolic is in the dish itself.

Tron of Borg

10-18-2001

Yep, then add a 30dbd amp, so 42dbd + 30 dbd amp is 72 Dbd, lol...
and then do that to the AP and the card, like range of 100 miles, screw the FCC.

10-18-2001

You guys might want to look into what happens when you add values on a log scale...

9+3!=12

10-18-2001

...and just tell me! I haven't looked at log paper in 10 years and I'm almost bald as is!

Tron Of Borg
(Founder of the Hair Club for IT)

(I'm not anything near bald. It just sounded like the right thing to say.)

10-16-2001	#1 (permalink)
Posts: n/a	Antenna Difference Sup guys I'm kinda new around "stumblin" the wireless community, so I got some question. What is the diff between parabolic antenna and a yagi? I thought both are for long distance, but what's the diff? and also, is the diff between parabolic 19db and 24 db big? 'coz the price diff is so big.... thats all 4 now....thanx in advance

10-16-2001	#3 (permalink)
Posts: n/a	19 dBd versus 24 dBd If you go with the parabolic you will be more than doubling your gain across the freq range; every 3 dB step doubles your gain... so the para has more than twice as much gain as the Yagi. Is this for point-to-point or portable? if this is for p2p your front-to-back ratio with the Yagi will be crap... Just my 2 centavos chris

10-17-2001	#5 (permalink)
Posts: n/a	Yagi vs para Hi again, I'm going to use it to connect my laptop with my cable modem connection at home. My campus is about 7 miles, blocked by trees and apartments. I figured that if I bought either a yagi or a para, I could point it to my campus so I can go wireless there. I think i prefer the 24Dbi one, and yes it's for point-to-point. You said that if I use a yagi, front to back will be crap. Isn't it supposed to be side to side? 'Coz a yagi is a directional antenna, so the front has the best range of coverage. Or mebbe i'm wrong, please correct me. Anyway, still cant decide to buy a yagi or a para. any suggestion welcomed. Thanx.

10-17-2001	#6 (permalink)
Posts: n/a	19 dBd vs. 24... The dB scale is <ahem> a LOGARITHMIC PROGRESSIVE SCALE... (man that's fancy) as opposed to a linear scale, it's like the Richter scale in that every step forward in the scale is a multiple of the previous number. Every 3 dB higher is actually double the energy/signal, every 10 dB is 10 times, 20 dB is a 100 times the signal strength, so on and so on. When an isotropic point source is radiating 360 deg. in free-space it exhibits 0 gain... so when you see " x# dBi" it's in reference to a number a certain multiple times above that. I'm more used to "dBd" which uses a single dipole as a reference point. The difference in dBi vs. dBd is, uhm, 2.14 or something close to that; 5 dBi = 3 dBd. SO ANYWAY... the difference in gain values between 19 dB and 24 dB is 5 dB, so roughly 2.6 times as more signal strength. Sorry this is so long, but this is what I do for a living. 'Cheers Chris

10-17-2001	#7 (permalink)
Posts: n/a	whoops Hey I just re-read this thread and I missed a point, I thought the original post was a question comparision between a 19dBd Yagi and a 24 dBd para... RATS. Ok so two different antenna designs which have the same gain will both be operating with (very roughly) the same power level. Sort of. Front-to-back ratio; the ration of signal at the peak gain point (0 degrees) as compared to the back (180 degrees), though a truer comparison would be from peak gain @ 0 deg. to everything from 90 deg. to -90 deg. the whole 180 degrees behind the antenna. A good FTB number is -25 to -30 dB down from peak gain; it's no big deal except in interference with users on the same frequency nearby; your signal could be picked up in the opposite direction thereby defeating the purpose of a directional antenna in the first place.

10-16-2001	#2 (permalink)
Posts: n/a	The difference between a yagi and a parabolic dish? A yagi is a series of elements one reflector, one driver (this is the only element that has the feed line hooked to it), and one or more directors. The more elements there are the higher the gain and the tighter the beam. A parabolic dish is just that a concave saucer like collector and a feed horn that is hooked to the feed line. The diffence between 19Db and 24Db is 5Db. You have to make the desicion to pay the extra money or not. What are you trying to accomplish? Later, D

10-17-2001	#4 (permalink)
Posts: n/a	Chris, Are you saying side by side that a 19DBd Para compared to a 19DBd Yagi is twice as good? Can you explain more for us that don't quite understand why the Para would outperform in such a huge way? Thanks.

10-17-2001	#8 (permalink)
Posts: n/a	How about this mod for an antenna? Take a Yaggie and use it as the horn of a parabolic! Let me see...18dbd Yaggie + 24dbd Parabolic = 42dbd! Freaking awesome! LOL That is assuming that dbd simply adds together and all the dbd of a parabolic is in the dish itself. Tron of Borg

10-18-2001	#9 (permalink)
Posts: n/a	hehe, theres more Yep, then add a 30dbd amp, so 42dbd + 30 dbd amp is 72 Dbd, lol... and then do that to the AP and the card, like range of 100 miles, screw the FCC.

10-18-2001	#10 (permalink)
Posts: n/a	You guys might want to look into what happens when you add values on a log scale... 9+3!=12

10-18-2001	#11 (permalink)
Posts: n/a	Please! Save me the trouble... ...and just tell me! I haven't looked at log paper in 10 years and I'm almost bald as is! Tron Of Borg (Founder of the Hair Club for IT) (I'm not anything near bald. It just sounded like the right thing to say.)

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