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* Radio & Equipment Questions [1]
* What equipment do I need? [2]
* So... how much does it cost? [3]
* Which cards have external antenna jacks? [4]
* What is low loss cabling? [5]
* What is a pigtail? [6]
* What is an antenna? [7]
* What kind of antenna are there? [8]
* OK, I\'ve now realised I don\'t understand what dB is... [9]
* What is this dBi Gain thing I keep seeing on antenna specs? [10]
* Is an omni directional antenna pattern really omni directional?
[11]
* Is there a limit to the height my antenna mast can be? [12]
* How far will my signal reach? Which antenna will see my mate _x_
km away? [13]
* What is the range of an Access Point where the signal needs to go
through walls? [14]
* What is the best type of antenna to link between X and Y? [15]
* What sort of cable should be used? [16]
* Can I get a link if there is no line-of-sight? [17]
* Do you have any tips when doorknocking to get someone\'s old
galaxy antenna? [18]
-------------------------
RADIO in radio signals it translates to "signal strength".
Visit "Using and understanding Decibels" [60] for a quick guide.
-------------------------
WHAT IS THIS DBI GAIN THING I KEEP SEEING ON ANTENNA SPECS?
HOW MUCH AN ANTENNA AMPLIFIES OR CONCENTRATES THE SIGNAL.
Basically it's how much more "powerful" the antenna is over an
imaginary dipole antenna. I say imaginary because nobody makes one,
but it would be an antenna that spreads the signal in every possible
direction, in the shape of a sphere. Such an antenna would have zero
Gain. So for example, a 24dBi gain parabolic grid is a very focused
antenna, it narrows the signal into a fine beam of coverage in one
direction. It doesn't use or provide any more power than a dipole, it
just focuses all that signal into one spot, so it goes farther.
A good analogy would be that of the light bulb in a torch. Unscrew
the cap and lens so you just have a bare bulb, and your immediate area
will be quite bright, but it doesn't go very far. This would be akin
to a 1 or 2dBi antenna. Now put the cap back on and the parabolic dish
will focus the light into a tiny little spot, and shine it down a
hallway. Your immediate area isn't very bright, except for that one
bright spot down the hall. This would be akin to a 24dBi parabolic
dish.
You can also use a water hose analogy (but then it gets even more
phallic, if that's even possible).
Further information along with some calculation examples [61] is also
available.
-------------------------
IS AN OMNI DIRECTIONAL ANTENNA PATTERN REALLY OMNI DIRECTIONAL?
YES, IN A HORIZONTAL PLANE.
It's more like a pancake. A low gain omni would look like a small fat
pancake (a pikelet), while a high gain would look like that same
pancake flattened out into a thin and long pancake (a crepe). Mmm...
pancakes.
There will always be a small blind spot (usually where the cable
comes in), but if that's orientated towards the ground then there
shouldn't be any problems.
-------------------------
IS THERE A LIMIT TO THE HEIGHT MY ANTENNA MAST CAN BE?
YOUR LOCAL COUNCIL AND STATE PLANNING BODIES SET THIS.
The Building Regulations 2006 [62] states:
431 - MASTS, POLES ETC
The report and consent of the relevant council must be obtained to an
application for a building permit to construct a mast, pole, aerial,
antenna,
chimney, flue, pipe or other service pipe which
�
(a) when attached to a building, exceeds a height of 3m above the
highest point of the roof of the building; or
(b) when not attached to a building, exceeds 8m above ground level.
-------------------------
HOW FAR WILL MY SIGNAL REACH? WHICH ANTENNA WILL SEE MY MATE _X_ KM
AWAY?
MAYBE.
There are lots of factors at play here, but as a basic guide: Omnis
and Cantennas (6 - 10dBi) will get you up to 2km, smaller directionals
(12 - 19dBi) will get you around 5 kilometres, and larger directionals
(20dBi+) will get you 10km or more.
This is of course affected by the antenna at BOTH ends. The best case
scenario is a well-aimed, correctly polarised high gain directional at
each end, and the worst is where both ends are using only the built-in
antenna in the device (typical range 50 - 100 feet).
A good antenna at one end will increase the range at which you can
connect to it, whatever antenna you are using at the other end. For
example, in a typical application like university campus, a powerful
omni or sector antenna will allow students and staff to connect from
all over the campus with only their client cards.
In the fairly common situation where one end has an omni and the
other a directional, the directional antenna will improve the signal
strength in both directions, compared to an omni at both ends. It will
pick up more signal from the omni, and transmit a better signal back
to it.
Of course, on a really long link, the curvature of the Earth becomes
a factor. See O\'Reilly [63]
-------------------------
WHAT IS THE RANGE OF AN ACCESS POINT WHERE THE SIGNAL NEEDS TO GO
THROUGH WALLS?
Help! I'm answering this question with wild guesswork. Anyone with
some real-world figures should fix this up! TYPICALLY ABOUT 30M.
30m is a wild guess. If you are trying to send your signal through
the walls of a tin shed, then chances are it won't penetrate at all.
If you live in a Japanese house with paper walls, you probably won't
notice the effect on range at all. For internal plaster walls held up
by a wooden frame with no insulation, expect the signal to attenuate
(weaken) by perhaps 3 decibels per wall - meaning it will be 1/2
strength after passing through 1 wall, 1/4 strength after 2 walls, 1/8
strength after 3 walls, etc. This attenutation (weakening) is in
addition to the attentuation suffered when the signal travels through
the air. Brick walls with insulation might attenuate your signal by as
much as 6db.
The only way to get a reliable answer is to test your equipment to
get real results.
-------------------------
WHAT IS THE BEST TYPE OF ANTENNA TO LINK BETWEEN X AND Y?
THAT\'S LIKE ASKING WHICH IS THE BEST VEHICLE TO GET FROM A TO B IN!
If you want to get from one side of a large metropolitan city to the
other, you might consider using many types of transport from your own
feet, through public transport, to flying a helicopter at great
expense. Similarly, there are many options available when it comes to
selecting an antenna to get connected.
If you've bought an AccessPoint [64] or a client adapter already,
chances are a small _omni-directional_ antenna has been included,
allowing you to make connections from about 50m away in every
direction given good conditions.
The cheapest long range antennas are the do-it-yourself style
(homebrew). You have the freedom to build whatever you want, providing
you have the expertise or can find someone to give you a hand. A
Cantenna [65] can manage a _directional_ link up to about 5km in the
right conditions and costs about $5. Do some in-depth technical
reading, spend a fortune and years of your life and you could build an
antenna array capable of sending signals to the moon - though it
probably won't do much good at sending signal from one end of a house
to the other.
In the retail world you typically get what you pay for (and yes there
are some bargains to be had). Spending around $150 should get you a
24dBi parabolic dish antenna capable of 30km links to a similar
antenna (this implies purchasing _2_ of them), but is probably a good
investment if you are serious.
-------------------------
WHAT SORT OF CABLE SHOULD BE USED?
Low loss coaxial cables [66] should be used to minimise the amount of
signal lost before reaching the antenna.
-------------------------
CAN I GET A LINK IF THERE IS NO LINE-OF-SIGHT?
SOMETIMES, YES.
The only way you can determine what will work for your location is to
borrow some equipment and do some tests with it. There are various
grades of link - if you use the cheapest and lowest gain equipment
your link may be low speed and/or marginal. If you want the fasted
speed possible you'll want to get the send and receive the strongest
signals possible. The problem with going through residential housing
is there are people and cars and moving about in your link path which
may make your link unstable. And if your link path goes through more
than a small amount brick, concrete or hill, your're going to have
trouble getting any link at all. You'll have to decide for yourselves
as to how tall is too tall for a mast. Then go get a mast which is as
high as you, your family and your neigbors will tolerate. Maybe a 1
metre mast extension on your TV aerial mast will be sufficient.
Every link is different, and the only true way to determine what
equipment you'll need is to test with different gear. You might get
away with a cantenna, or maybe you'll need a 25dB parabolic antenna.
The only way to know for sure is to test the gear out. If you don't
want to spend big bucks on gear see if you can get a hold of old
Galaxy or Austar Pay TV 2.4Ghz dishes, which can be made to work with
802.11b/g with small modifications.
-------------------------
DO YOU HAVE ANY TIPS WHEN DOORKNOCKING TO GET SOMEONE\'S OLD GALAXY
ANTENNA?
USE YOUR MANNERS AND SOME COMMON SENSE.
Be polite, courtious and respectful, when asking, and be sure that
it's really a galaxy and not a strange UHF antenna.
---
CAN\'T FIND THE ANSWERS TO YOUR QUESTIONS? Try looking through all of
the questions listed on TheEvolvingFAQ [67]. If you still can't find
answers, ask your questions here [68].
Links:
------
[1] http://melbournewireless.org.au/#radio___equipment_questions
[2] http://melbournewireless.org.au/#what_equipment_do_i_need_
[3] http://melbournewireless.org.au/#sohow_much_does_it_cost_
[4]
http://melbournewireless.org.au/#which_cards_have_external_antenna_jacks_
[5] http://melbournewireless.org.au/#what_is_low_loss_cabling_
[6] http://melbournewireless.org.au/#what_is_a_pigtail_
[7] http://melbournewireless.org.au/#what_is_an_antenna_
[8] http://melbournewireless.org.au/#what_kind_of_antenna_are_there_
[9]
http://melbournewireless.org.au/#oki_ve_now_realised_i_don_t_understand_what_db_is_
[10]
http://melbournewireless.org.au/#what_is_this_dbi_gain_thing_i_keep_seeing_on_antenna_specs_
[11]
http://melbournewireless.org.au/#is_an_omni_directional_antenna_pattern_really_omni_directional_
[12]
http://melbournewireless.org.au/#is_there_a_limit_to_the_height_my_antenna_mast_can_be_
[13]
http://melbournewireless.org.au/#how_far_will_my_signal_reachwhich_antenna_will_see_my_mate_x___km_away_
[14]
http://melbournewireless.org.au/#what_is_the_range_of_an_access_point_where_the_signal_needs_to_go_through_walls_
[15]
http://melbournewireless.org.au/#what_is_the_best_type_of_antenna_to_link_between_x_and_y_
[16]
http://melbournewireless.org.au/#what_sort_of_cable_should_be_used_
[17]
http://melbournewireless.org.au/#can_i_get_a_link_if_there_is_no_line_of_sight_
[18]
http://melbournewireless.org.au/#do_you_have_any_tips_when_doorknocking_to_get_someone_s_old_galaxy_antenna_
[19] http://melbournewireless.org.au/?TheEvolvingFAQ
[20] http://melbournewireless.org.au/?PCMCIACradle
[21] http://melbournewireless.org.au/?Pigtail
[22] http://melbournewireless.org.au/?NConnector
[23] http://melbournewireless.org.au/?CoaxialCable
[24] http://melbournewireless.org.au/?LMR-400
[25] http://melbournewireless.org.au/?OmniAntenna
[26] http://melbournewireless.org.au/?LoS
[27] http://melbournewireless.org.au/members/tib/
[28] http://melbournewireless.org.au/?PCMCIACradle
[29] http://melbournewireless.org.au/?Pigtail
[30] http://melbournewireless.org.au/?LMR-400
[31] http://melbournewireless.org.au/?Antenna
[32] http://melbournewireless.org.au/?Cantenna
[33] http://melbournewireless.org.au/?NConnector
[34] http://melbournewireless.org.au/?GalaxyAntenna
[35] http://melbournewireless.org.au/?LMR-400
[36] http://melbournewireless.org.au/?EnterasysCards
[37] http://melbournewireless.org.au/?HardwareDatabase
[38] http://melbournewireless.org.au/?LMR-400
[39] http://melbournewireless.org.au/?CoaxialCable
[40] http://melbournewireless.org.au/?CoaxialCable
[41] http://melbournewireless.org.au/?LMR-400
[42] http://melbournewireless.org.au/?LMR-400
[43] http://melbournewireless.org.au/?RG-8
[44] http://melbournewireless.org.au/?RG-213
[45] http://melbournewireless.org.au/?NConnector
[46] http://melbournewireless.org.au/?LMR-400
[47] http://melbournewireless.org.au/?LMR-400
[48] http://melbournewireless.org.au/?RG-213
[49] http://melbournewireless.org.au/?NConnector
[50] http://melbournewireless.org.au/?OmniAntenna
[51] http://melbournewireless.org.au/?ParabolicAntenna
[52] http://melbournewireless.org.au/?HelicalAntenna
[53] http://melbournewireless.org.au/?YagiAntenna
[54] http://melbournewireless.org.au/?PatchAntenna
[55] http://melbournewireless.org.au/?PanelAntenna
[56] http://melbournewireless.org.au/?WaveGuide
[57] http://melbournewireless.org.au/?Cantenna
[58] http://melbournewireless.org.au/?WaveGuide
[59] http://wirelessanarchy.com/#Antenna
[60] http://www.columbia.edu/~fuat/cuarc/dB.html
[61] http://melbournewireless.org.au/?PowerAndGainToDecibels
[62]
http://www.legislation.vic.gov.au/Domino/Web_Notes/LDMS/LTObject_Store/LTObjSt6.nsf/DDE300B846EED9C7CA257616000A3571/D238ED96B9591334CA25793400007148//06-68sr020bookmarked.pdf
[63] http://www.oreillynet.com/cs/weblog/view/wlg/197
[64] http://melbournewireless.org.au/?AccessPoint
[65] http://melbournewireless.org.au/?Cantenna
[66] http://melbournewireless.org.au/#What_is_low_loss_cabling?
[67] http://melbournewireless.org.au/?TheEvolvingFAQ
[68] http://melbournewireless.org.au/?FAQYourAdditions
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