The CATFISH thread - external antenna choice and use.

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naiku
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Joined: 25 Feb 2008
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PostPosted: Thu Jul 23, 2009 16:09    Post subject: Reply with quote
Murrkf wrote:

From what I understand of your setup, put the panel antenna outside and point it at the second house. Put the router to auto for antenna choice. Put the router in the second house in the basement window. Set it to auto as well, and put it in repeater mode.

Should work well.


I think that is what I will do, just need to figure out where to mount the panel antenna. The house it will go on is T shaped, where I had planned to mount the antenna it would be pointing right at the vertical part of the T. So I either have to run longer coax and mount it on the horizontal part of the T, or move it up higher. The window in the second house is on the back (not facing the first house) but should be better than concrete!

Once I figure out where to mount the panel, I just need to figure out how much coax I need.
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Murrkf
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PostPosted: Thu Jul 23, 2009 16:27    Post subject: Reply with quote
If you use low loss coax, I would not worry TOO much about the length.
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SIG:
I'm trying to teach you to fish, not give you a fish. If you just want a fish, wait for a fisherman who hands them out. I'm more of a fishing instructor.
LOM: "If you show that you have not bothered to read the forum announcements or to follow the advices in them then the level of help available for you will drop substantially, also known as Murrkf's law.."
Murrkf
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PostPosted: Fri Aug 21, 2009 13:29    Post subject: Reply with quote
The comments to this article are definitely worth reading...

http://www.instructables.com/id/10--WIFI-16dBi-Super-Antenna-Pictorial/

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SIG:
I'm trying to teach you to fish, not give you a fish. If you just want a fish, wait for a fisherman who hands them out. I'm more of a fishing instructor.
LOM: "If you show that you have not bothered to read the forum announcements or to follow the advices in them then the level of help available for you will drop substantially, also known as Murrkf's law.."
embguy
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Joined: 24 Nov 2008
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PostPosted: Thu Sep 03, 2009 16:39    Post subject: Reply with quote
Radioman193 wrote:
16 dBi WIFI Wireless omniAntenna +Magnetic Base

Gain: 16dbi
Connector: SMA male with pin female connector
Frequency: 2.4G
VSWR: <1.5:1
Impedance: 50Ω
Power: 50W
Ambient temperature: -40~80?
Weight: 180g
Cable length: 3M

1 have 10 of these "on different Routers" and thay are AWSOME!
with the wrt300n v1.0 i can pickup my wifi for over a MILE and still able to stream a movie off my server.

I am trying to extend my signal to another house on the same side of the street. (Details --> http://www.dd-wrt.com/phpBB2/viewtopic.php?t=57117&highlight=)
Can you pickup the signal in your house when you are beside the house at the end of your block?

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youngstud2476
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PostPosted: Sat Oct 24, 2009 7:57    Post subject: Trying to put my ddwrt router 60 feet from the external ante Reply with quote
when i attempt this i loose way too much signal it goes from -30 to -97 what could cause this??? tx rx set to auto ect repeater mode ect
Murrkf
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Joined: 22 Sep 2008
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PostPosted: Sat Oct 24, 2009 11:12    Post subject: Re: Trying to put my ddwrt router 60 feet from the external Reply with quote
youngstud2476 wrote:
when i attempt this i loose way too much signal it goes from -30 to -97 what could cause this??? tx rx set to auto ect repeater mode ect


"this"?

Search google for "wifi cable loss"

_________________
SIG:
I'm trying to teach you to fish, not give you a fish. If you just want a fish, wait for a fisherman who hands them out. I'm more of a fishing instructor.
LOM: "If you show that you have not bothered to read the forum announcements or to follow the advices in them then the level of help available for you will drop substantially, also known as Murrkf's law.."
ad5mb
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Joined: 12 Oct 2008
Posts: 386

PostPosted: Sun Jan 10, 2010 17:14    Post subject: Reply with quote
time to clarify things in re omnis:

16 db omni is bogus. the images shown earlier of 16 db omnis are 9 db omnis. the seller is a liar.

15 db is the practical limit of a gain omni.

an omni with gain is a stack of omnis with carefully designed non radiating spacers called phasing elements between. These spacers are 1/2 wavelength long. remember from science class that like charges repel.

in the graphic below,

    | is an omni element
    || is a phasing element that does not radiate
    + & - indicate polarity of the signal on the radiating element at the moment of observation:


+
|
-
||
-
|
+
||
+
|
-

These three elements are radiating RF, but the middle element is out of phase with the other two. the RF energy from the + below repels the RF energy from the + above the phasing element. this causes the energy to compress horizontally.

if you could see RF energy, and RF of equal strength made a crisp red line, the RF energy from a low gain omni would look like a cross section of a bagel:

The radiation pattern from a 4 db gain omni from L-com.com

4 dbi gain omni



A higher gain antenna will have more radiating elements; so it will have more compression. the radiation pattern from an 8 dbi gain omni:

8 db gain omni



A very high gain antenna will compress the same energy even more. if the bagel in the 4 db example was a 1 ounce bagel, the same amount of material would come out like a 1 ounce pancake in a high gain antennaq. the radiation pattern from a 12 dbi gain omni:

12 dbi gain omni



Same amount of RF energy, distributed more efficiently.

antenna gain is bidirectional; it benefits both transmit and receive

regarding ground planes:

The ground plane needs to be 1/4 wavelenth in radius. you need no less than 4 for an omni. 1/4 wavelength radius is 1/2 wavelength in diameter.

a wavelength at 2.4 ghz = 5 inches. so if you have a 2.5" flat metal plane, grounded, at the base of the antenna, you have all the ground plane you need, no matter how high up the antenna is.

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Conventional wisdom among radio guys is that $1 spent on antennas is worth $10 spent on amplifiers. Solve RF problems with antennas to the greatest extent possible before increasing power.
ghz24
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Joined: 15 Jan 2010
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PostPosted: Mon Jan 25, 2010 9:58    Post subject: Reply with quote
Hi

didn't see any posts on slotted waveguides I think these

push the 15 dbi limits to omni-directional antennas and have alot of good features can be made as high gain directionals to, almost as good as a 3' dish almost

http://www.trevormarshall.com/waveguides.htm

kuddos on this page but I feel I must disagree regarding canntanas being refered to as "aperture limited dipoles". Properly designed and built they are more like a circular waveguide with the reflected wave adding to the signal.
Optimized to the right dimensions they work very well
ad5mb
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PostPosted: Mon Jan 25, 2010 13:55    Post subject: Reply with quote
Quote:
Optimized to the right dimensions they work very well


There's the key. Precision Pringles cans. Cutting a dipole with dykes and leaving the end as is. 5" wavelength means a tiny error is a major percentage of a wavelength.

_________________
Conventional wisdom among radio guys is that $1 spent on antennas is worth $10 spent on amplifiers. Solve RF problems with antennas to the greatest extent possible before increasing power.
ghz24
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Joined: 15 Jan 2010
Posts: 28

PostPosted: Tue Jan 26, 2010 3:36    Post subject: Reply with quote
I'll agree pringles cans are to narrow to work (as a waveguide) and the if in "if dimentioned properly" should have been an iff
I built mine as a test rig to compare future projects against. plus I had all the stuff ,lmr 400 and clamp on N-connectors, and I don't need them any more thanks to dd-wrt
btw: thank you to all who contributed to thiS firmware it's awsome !!

what do you make of the slotted waveguides? Are you familiar with these?

Is there less loss than the staggered coax
collinears or brass tubing models or are they mostly usefull for their horizontal polarization
el-pancho
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Joined: 25 Jan 2010
Posts: 4

PostPosted: Wed Jan 27, 2010 1:17    Post subject: Reply with quote
I read something on the thread about turning off the unreplaced antenna. Is that right. How can I do that?
ghz24
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Joined: 15 Jan 2010
Posts: 28

PostPosted: Sun Feb 21, 2010 6:42    Post subject: Reply with quote
I think the setting for antenna selection is available through the web gui under the wireless tab then advanced settings set tx antenna and rx antenna both to ether right or left default is auto I'm thinking if rx and tx antenna are both set to right then left is virtually disabled. Hope this is what you were looking for.

Murrkf wrote :
"Antennas don't create more powerful signals to get out of basements and through concrete"

Sorry this is just wrong. The antenna gain, on either end affects your calculated link budget a high gain antenna can be the difference between having a viable link and having no connection
In short an antenna can create a more powerful signal and more sensitivity.
bryanchewy
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Joined: 29 Dec 2008
Posts: 15

PostPosted: Mon Aug 30, 2010 2:36    Post subject: turn off one ant or leave on auto Reply with quote
I have been reading and reading but haven't really found a solid answer. Hopefully someone can help me out.

I have a linksys WRT54G-TM with dd-wrt on it set up in my neighbors house (300 feet line of site) and have it set as client bridge. I have both stock ant set to auto.

This connects to a linksys WRTu54G-TM (which is not dd-wrt compatible yet) in my house(where internet is) running with a d-link omni ant (cable is about 2 feet long to router). I have this ant in my front window looking at his house. I think the dlink is 5 or 7 dbi omni and this router only has one ant.


This is what dd-wrt shows me on the status page of the bridge:

Signal Noise SNR signal quality
-52 -92 40 52%

Right now I have all of my pcs connected by wire in my house except my laptop. He has one pc and a laptop at his house.

I have connected (with wire) a netgear wgt624 v4 (running stock as a AP...has different ssid than my house and different channel than my house and the bridge) to the client bridge at his house so he can connect his laptop wirelessly. I also have a desktop wired into the netgear at his house.

The problem is that if i run a speed test(spedtest.net) at my house on any of my pcs (wired or wireless) i might get 4 down and .7 up. But if i have him run right after i did mine, he will get 1.5 down and .7 up.

Do i have settings wrong or do i need to get a directional ant at his house on the bridge and then set the bridge to just use that ant(not both on auto)?

Or would there be something else causing the problem. How do i check for actual speed across the pc's? I mean they say 54mbp, but i know we're not getting that high.

Thanks so much for any input. I have read myself into confusion. LOL
yousaf465
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Joined: 12 Sep 2010
Posts: 380

PostPosted: Mon Jan 10, 2011 7:08    Post subject: Reply with quote
Wikipedia mentions a 12-15db gain with a Wokfi http://en.wikipedia.org/wiki/WokFi, has anyone every experienced it ?
ghz24
DD-WRT Novice


Joined: 15 Jan 2010
Posts: 28

PostPosted: Mon Mar 19, 2012 21:15    Post subject: wok-fi Reply with quote
I don't recommend them. That doesn't mean they won't help a flat reflector gives ~3 dB gain and reduces noise from the rear.

If you have an external removable antenna go with a pig tail and a feed for better "illumination" .

If not this may be your best option.
Part of the attraction of these wok reflectors has to do with putting the radio close to antenna ( in the focus) so no loss in the usb cord like a pigtail and even good coax causes, with dd-wrt you can rig up a POE to put the router where ever you need it so less advantage.

This a calculator to determine performance of imperfect parabolic dishes

http://www.satellite-calculations.com/Satellite/gainloss.htm
You may find it helpful in wading through the hype and "personal endorsement" and estimate what performance you can hope for. ( i think that calculator also assumes perfect illumination which you won't have from an omni feed) So you should probably subtract another ~3 dB.
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