The CATFISH thread - external antenna choice and use.

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ruddles
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PostPosted: Wed Dec 10, 2008 12:36    Post subject: The CATFISH thread - external antenna choice and use. Reply with quote
Based on Donny's Peacock, I propose the CATFISH thread..
WHy, cos its easy to search for.. :;


Idea - to keep a base for info for building, choosing and using external antenni with your router -

Learn about building the good old yagi antenna (directional)

http://vk5dj.mountgambier.org/Yagi/Yagi.html

Excellent thread about how to build a panel antenna
http://www.dd-wrt.com/phpBB2/viewtopic.php?t=5026

Learn about building the good old cantenna (Circular waveguide antenna (Directional)

http://www.saunalahti.fi/elepal/antenna2calc.php

Learn about various options...

http://www.radiolabs.com/Articles/wifi-antenna.html

http://www.educypedia.be/electronics/electroniccalculatorsant.htm


Try to understand gain, milliwats, dbi, dbd etc etc..

http://www.aubraux.com/design/dbm-to-milli-watts-calculator.php


I want to start this thread, not Broadcomm specific, but as a way for folks to learn about external antennas, and how they can help in a point to point situation.

Basically, a theoretical antenna transmits all around, and receives all around..
Its a lawn sprinkler.. :)

You only have so much pressure to the sprinkler.. if you focus it in one direction, you have more pressure (in one direction)..
that is a reasonable analogy of gain.

IF you concentrate the effort in one direction, you get a better output, (A longer squirt Wink ... it can also add to the receive signal 'gain' becuase it is focussed. (Concentrated in one direction which also means the receiver is only looking in this direction)

A good antenna works both on transmit, AND receive.

Increasing tx power on the router, ap, device, or whatever - works on transmit, but NOT on receive.. so you may get the signal OUT more, but the input is crippled and not in line with the increased output.

With a good antenna, BOTH the output and input are increased..

For every doubling of tx power in mW, we increase the power by apx 3dB.. for every increase of 3dB, we increase the effective output power in mw by a factor of 2 times the original power.

ie, 20 mW output power, to a 3dBi antenna, = 40 mW effective radiated power (in simplistic terms) , AND if using a good antenna, the receive gain is more or less the same. a weak signal is 'amplified' by the antenna to give a stronger signal to the wifi receiver. (Apx double what we would have without it.

So win win...

Adding tx power, WITHOUT an increase in receive signal strength does not accomplish much.

Power hacks are mostly non productive - apart from causing overheat, non linearity (crappy signal) etc.

Lots of router / AP's have two antenni, they are used in receive mode for selecting the best signal (Diversity - again, in simple terms). IF you use an external antenna, turn this off.. use one antenna (the one with the external added) for tx and rx.. the other is unused.
Diversity can help in situations with reflected signals, as an omidirection antenna has to put up with. but, becuase we are now, presumably, using directional antennas (point to point) not needed.

I hope this is a start, not to resort to which antenna is best.. although it is unrealsitic not to expect some kind of input in that sort. :)

Hope it helps to at least grasp the basics.

Rudds.
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Donny
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PostPosted: Wed Dec 10, 2008 14:31    Post subject: Reply with quote
You gotta put the biquad dish antenna links in....

And this thread has some fabulous information:

http://www.dd-wrt.com/phpBB2/viewtopic.php?t=43817

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Last edited by Donny on Thu Dec 11, 2008 2:03; edited 1 time in total
JN
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PostPosted: Thu Dec 11, 2008 1:52    Post subject: Re: The CATFISH thread - external antenna choice and use. Reply with quote
I would add, if you choose to use an amplifier, make sure its a bidirectional amp, with receive boost as well.
ruddles
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PostPosted: Thu Dec 11, 2008 2:11    Post subject: Reply with quote
Good point JN, thanks for the input.

And to add, if one chooses an external amp with rx amp built in, READ CAREFULLY the input requirements to the amp, ie, the power level, ususally expressed in dBm (Link to calculator on first page of this thread for converting to milliwatts mW)
So, if your new amp wants no more than 15 dBm, you would have to REDUCE the power output of your wrt54g which is set at 70mW (15dBm is apx 30mW.
Failing to do this will possibly damage the amp, WILL lead to overdriving the amp giving a poor quality signal (Errors) and WILL cause interference to other users.




There are legal limits as to the erp (Effective radiated power) for each country, it is worth checking ! . Even adding a high gain rubber duck type antenna may well cause you to break the law in your area. Check and use with care.


Rudds
Donny
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PostPosted: Thu Dec 11, 2008 2:55    Post subject: Reply with quote
If we're going to talk externals, we gotta get Doramius in here.....

Here is his thread on replacing the antenna leads on a non detachable antenna router. Nice work:

http://www.dd-wrt.com/phpBB2/viewtopic.php?t=43167&

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ruddles
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PostPosted: Thu Dec 11, 2008 11:08    Post subject: Reply with quote
Thanks Donny (Hows the toe ?) Shocked
Very Happy

Great link.
Please add links to any antenna designs you feel are, a. GOOD, and, b. WORK, all appreciated

For any add on external antenni to a non removable antenna unit, I think the best advise is to buy a pigtail connector with the item you want, some firms specialise and make them up for you, buy one with both ends the same (revsma, revtnc or ntype) - ask to have one made -this presumes you have no access to crimpers and no old router to pinch parts from. Cut the pig tail in half, then use these as the connectors.
Because I install LOTS of wifi units for yachties.. I bought a crimper set (Around 40 USD) and the appropriate crimp connectors and cable. RG316 for most internal add ons..

Thanks for the input (again !)
ps, did I ask how your toe is ?? Laughing

What this thread needs now is a definitive guide to all the advanced wireless settings, in great detail as appertains to an external connector, I have touched on it, but it needs expanding ? any volunteers ?

Rudds
Donny
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PostPosted: Thu Dec 11, 2008 14:06    Post subject: Reply with quote
ruddles wrote:

ps, did I ask how your toe is ?? Laughing



It BURNS...IT BURNS. Oh. Wait. No..that's from the holy water. But the blistering has almost started to go down.

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gene
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PostPosted: Thu Dec 11, 2008 17:14    Post subject: Reply with quote
wow, great thread, donny has not mentioned the peacock once here yet. Very Happy However I do have a serious question on this subject. I have an old signal booster that I used when I had a wrt54B unit. it was made by linksys, designed to work with the linksys wrt54b unit, I know nothing about electronics but would it also work with my 'G' device signals since the connections are nothing more than inserting to the antenia jacks ?
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ruddles
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PostPosted: Thu Dec 11, 2008 21:28    Post subject: Reply with quote
Hiya Gene
answer in 802.11G, is almost certainly NO, unfortunately.
However, it will work at B if you set the router to B only output. For most uses it will still offer a good dl speed. but the b and g specs are differnt for the amp.
Rudds
KeithB
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PostPosted: Fri Jan 09, 2009 20:18    Post subject: WNR834B v2 antenna replacment / upgrade Reply with quote
Here's a thread I submitted about easy antenna replacement on the WNR834B v2 router a few months ago.

Here's a link to pictures of the finished project.

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Last edited by KeithB on Fri May 01, 2009 23:52; edited 1 time in total
ad5mb
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PostPosted: Fri Jan 09, 2009 22:34    Post subject: Reply with quote
Patch antennas for pointing at a neighboring antenna through a window. Hangs flat against the glass.

Patch antenna for Velcro-ing to the lid of a laptop.

Yagi for pointing downwind in high-wind areas.

Dish for crosswind in high-wind areas.

Coaxial colinear for homemade high gain omnis.

Slotted waveguide if you have a milling machine you can't find a use for.

General antenna knowledge:

High gain omnis achieve their gain by flattening the radiation pattern. More out = less up and down. You can be standing under a 15 dB gain omni 25 feet up and not see it with a laptop. Point this out to people who whine about cellphone towers in the neighborhood.

Large diameter active elements have a wider low-SWR bandwidth. If you want to make a quality Yagi, use copper pipe, not copper wire.

Directional antennas with similar gain should have similar beamwidth. Yagi, panel, should be very similar.

You have to double the length of a yagi to get double the gain. 15 dB is the practical limit.

http://www.freeantennas.com/2400/

http://www.freeantennas.com/tilt-over-tower/index.html

http://www.freeantennas.com/

Calculations for long links:

http://www.terabeam.com/support/calculations/index.php

slotted waveguide
http://nuke.freenet-antennas.com/modules.php?name=News&file=article&sid=1

http://martybugs.net/wireless/collinear.cgi

loop yagi
http://www.om3rkp.cq.sk/articles.php?lng=en&pg=4

http://binarywolf.com/249/parabolic.htm

yagi and dish back to back on a rotator
http://www.amilabs.com/rooftopstumbler.htm

http://trevormarshall.com/waveguides.htm

theory for the rf addicts:
http://www.ifwtech.co.uk/g3sek/diy-yagi/

http://www.dxzone.com/catalog/Antennas/WiFi/

http://www.educypedia.be/electronics/antennawlanparabola.htm

http://www.wikarekare.org/

http://www.wirelessanarchy.com/#Antenna


Last edited by ad5mb on Wed Jan 28, 2009 14:22; edited 1 time in total
dustout
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PostPosted: Wed Jan 28, 2009 7:47    Post subject: Reply with quote
this post it very helpful, however i would like clarification on one thing.

using a yagi antenna (the below one)
http://www.hyperlinktech.com/web/hg2415y.php
would i receive any benefit from the built in amplifier found on the Buffalo WHR-HP-G54 as compared to the normal setup found on the Asus WL-500g Premium
Donny
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PostPosted: Wed Jan 28, 2009 14:00    Post subject: Reply with quote
dustout wrote:
this post it very helpful, however i would like clarification on one thing.

using a yagi antenna (the below one)
http://www.hyperlinktech.com/web/hg2415y.php
would i receive any benefit from the built in amplifier found on the Buffalo WHR-HP-G54 as compared to the normal setup found on the Asus WL-500g Premium


Need to know what you are trying to do....

That being said, you likely don't need an amp.

I have seen some posts that suggest problems (lousy throughput?) with one of the WL500 routers btw. WL520 seems good.

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ad5mb
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PostPosted: Wed Jan 28, 2009 14:20    Post subject: Reply with quote
1) The effects of the amplifier and the antenna would add up at the far end.

2) The antenna would provide a benefit at the amplifier end, but not the amplifier. amplifiers improve outbound signals.

antennas are always the first, best solution to signal strength problems. solve RF problems with antennas to the extent possible, and amplifiers to the extent necessary.

That is called a "Best Practice" in engineering.
dustout
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PostPosted: Wed Jan 28, 2009 17:52    Post subject: Reply with quote
Donny wrote:
Need to know what you are trying to do....

That being said, you likely don't need an amp.

I have seen some posts that suggest problems (lousy throughput?) with one of the WL500 routers btw. WL520 seems good.

i am trying to build a predator

http://www.i-hacked.com/index.php?option=com_content&task=view&id=261&Itemid=42&mosmsg=Item+successfully+saved.
it is mostly for looks, but i will need it on occasion when my internet goes down to connect to the free wifi across the street (approx 250m away)

any router will do, the WL500 was on sale ($89 canadian) so that is why i liked it. Also it was white and that will look good on the project. What router would you suggest?

ad5mb wrote:
1) The effects of the amplifier and the antenna would add up at the far end
...
That is called a "Best Practice" in engineering.

so your saying an amplifier will help increase the range when i am sending out a signal, but since the limiting factor in my situation is the free crappy wifi i would receive no gain from it due to it's terrible job of sending me a signal.

However if i were able to add a booster to the free crappy wifi then i would receive added range, because there ability to send me signals would increase.

Yes that makes sense, thank you for clarifying that issue Razz
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