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Author Topic: 2 meter dipole basics?  (Read 1567 times)
KB3QGV
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Posts: 4




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« on: April 22, 2013, 08:52:11 PM »

Good evening, y'all....

having just gotten up and running with my yaesu ft-60r (which i highly recommend for walkaround use), I want to set up a 2 meter antenna (i assume dipole is the best entry level design) that I can guy to my roof/chimney/your advice for best location.

things im looking for include the best way to create the dipole itself. while i am good with my hands, this is my first crack at a home brew, and I want to do it right because i learn by doing.

Best techniques for grounding the antenna?
can I use PVC pipe for framing out the antenna?
best type of connectors to use on the cable?

Thanks in advance.

kb3qgv
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KB4QAA
Member

Posts: 2450




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« Reply #1 on: April 22, 2013, 10:07:44 PM »

Welcome!
  
Since you are interested building antennas, one of the most satisfying and cost effect aspects of hamming, I strongly urge you to purchase a copy of the ARRL Antenna Book.  You will refer to it for years to come.

Two meters polarization conventions:
-FM/Repeaters, Vertical
-SSB/CW/Weak signal work: Horizontal

A 2m dipole antenna (half wave) is probably a very poor choice due to several factors:  hard to hang for FM work, other antennas are much simpler to build, gain antennas which beat the pants off it are easy to build or buy.

The simplest antenna you could build for FM work is a "1/4 wave length ground plane".  You can build it with some solid wire and an SO-239 connector.  Google that and you will find directions.  (don't let anyone try to convince you on Jpoles. They are more complex, don't perform any better and tend to radiate signals down the feedline)   "Why yes! I'm a ground plane man. How did you know?" Smiley

The formula 234/Mhz = element length in Ft.  Gives you the dimension for the elements. Commit this to memory, and it will serve you well for years.

Use whatever connectors fit your radio/antennas, or are handy.

PVC is fine for work at UHF and below; many hams use it.

cheers, bill
« Last Edit: April 22, 2013, 10:10:10 PM by KB4QAA » Logged
KB3QGV
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Posts: 4




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« Reply #2 on: April 22, 2013, 10:59:10 PM »

Good Morning Bill and All,

Bill, can I assume from the "cheers" that you are of British heritage? very cool if so.

Is this what you are referring to by a ground plane system?

http://www.qsl.net/wrav/2mground.htm

this seems to me to be a hyper-easy build! and i could concievably park this on a pvc mount to the side of the high point of my house. could you provide some information on how to properly ground this antenna, or is the ground built in on the sheath lead? I ask because as a child, my dad sunk a pipe in the ground and ran some flat meshed grounding cable from the antenna to the pipe. not sure if he was overdoing it for safety or not.
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IZ2UUF
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Posts: 63


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« Reply #3 on: April 23, 2013, 12:12:34 AM »

having just gotten up and running with my yaesu ft-60r (which i highly recommend for walkaround use), I want to set up a 2 meter antenna (i assume dipole is the best entry level design) that I can guy to my roof/chimney/your advice for best location.

things im looking for include the best way to create the dipole itself. while i am good with my hands, this is my first crack at a home brew, and I want to do it right because i learn by doing.

Best techniques for grounding the antenna?
can I use PVC pipe for framing out the antenna?
best type of connectors to use on the cable?

Hello Joseph.

Consider also the J-pole antenna: it is very simple and it has a better gain over the ground plane.
There are hundreds of J-pole projects on the internet, made of a great variety of materials.
It can also be made by cutting some notches in a piece of 300 Ohm twin-lead cable: I have one folded in my backpack for quick /P operations.

Davide
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Davide IZ2UUF - FISTS #16285 - SKCC #9531 - JN45nk
SWMAN
Member

Posts: 586




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« Reply #4 on: April 23, 2013, 07:28:55 AM »

 I built a real easy to make vertical dipole designed by W7LPN. It is made of quarter inch copper tubing and PVC. It works real well with my FT-60r talkie. It works for 440 also. Google W7LPN Vertical Dipole and it will show you how to make one. Good luck Jim and 73  W5JJG
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WB6BYU
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Posts: 13486




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« Reply #5 on: April 23, 2013, 10:40:27 AM »

Quote from: KB3QGV

Is this what you are referring to by a ground plane system?

http://www.qsl.net/wrav/2mground.htm

this seems to me to be a hyper-easy build! and i could concievably park this on a pvc mount to the side of the high point of my house...



Yes, that's a good example, and they are, indeed, very easy to build.
They also work about as well as anything else of an equivalent size,
including j-poles.

I build mine using an 18" vertical whip, as that allows me to cut two
top sections out of a single 36" length of brass brazing rod (which is
stiffer than copper wire).  The radials are #14 solid copper wire from
a piece of ROMEX or whatever I have laying around.  If you use the
18" length for the top whip, then make the radials 24" long.  (Yes,
it works fine, in spite of the formulas you see in most places.  These
dimensions came from an article in QST by W6BCX, who invented the
half square and the Bobtail Curtain.)

I mount mine using PVC pipe by running the cable down inside the pipe
and letting the connector flange sit on the top.  The weight of the
coax holds the antenna in place.  If the bottom of the pipe sits on the
ground then at some point you'll need to put a coax T connector in
the pipe to bring the coax out the side - this may be easier if you cut
off the side of the T so the coax doesn't have to make as sharp of
a bend.  In practice I stick the PVC mounting parts into the top of
a stronger mast (PVC masts will bend if you try to get much height)
so I make up short sections of PVC with a modified T in the middle:
the ground plane goes on the top and the bottom slips inside my main
mast up to the T.  (I have some using 1/2, 3/4 and 1" PVC depending
on the mast I am using.)  I use them for portable operation and they
are very easy to set up.  For permanent installations you can use a
metal mast in the same way and slip the coax down inside it, but
again, it has to come out the side at some point if the base of the
mast is sitting on the ground.  EMT conduit can be used instead of
PVC if you want.

The best way to ground the antenna is to bring the coax down to
ground level and install a lightning arrestor connected to a ground
rod (and tied back to the ground rod at the electrical panel with
#6 wire according to code) then another coax from there to the
operating position.  Whether you need a ground or not depends
on the chances of a lightning strike in your area:  some of us don't
have to worry about it, while some other hams get their antennas
hit 2 or 3 times a year.
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