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Author Topic: BEST 2 meter apartment antenna ?  (Read 5410 times)
KZ1X
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« Reply #15 on: August 30, 2007, 05:14:34 PM »

http://www.qsl.net/w4sat/tiny2.htm

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KE3WD
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Posts: 5689




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« Reply #16 on: August 30, 2007, 06:03:56 PM »

The actual number of magmount antennas for 2 meters that can actually take 75W of RF is extremely low.  

This particular radio has melted down quite a few loading coils and while the antenna is cooking it doesn't do anything good to those expensive final transistors...


Keep your power level turned down low.  


You should be looking at antennas and not higher power levels anyway.  

The suggestions so far have been good ones.  

Also keep in mind that VHF is line of sight for local comms, the higher above ground you can place an antenna, the more repeaters and simplex contacts you should be able to make.  


KE3WD
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KC2MPG
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Posts: 65




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« Reply #17 on: August 30, 2007, 08:37:53 PM »

KE3WD: Would you recommend a higher gain anyenna with lower power, or would the higher gain make the the rf more dangerous to be near in the room?
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KE3WD
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« Reply #18 on: August 30, 2007, 09:29:40 PM »

>>KE3WD: Would you recommend a higher gain anyenna with lower power, or would the higher gain make the the rf more dangerous to be near in the room?<<

First, you've got to come to grips with the notion that more RF power is the answer.  It usually isn't, and remember, as Amateur Ops we are supposed to use just enough power to establish communications.  

The 75W Icom rig is an FM rig, no?  

What are your intended communications goals?

If it is hitting repeaters, odds are pretty good that you will never need that kind of power level.  

If it is hitting distant repeaters or talking simplex, a better antenna, up high and in the clear, will do the job much better than even 1,000 watts inside the room with you will.  Honest.  

That radio was really designed for the mobile ham, mounted in a vehicle, where there may be some distance from repeater at times, like in a rural setting.  

Are you far away from any repeaters?

Using 75W to hit a repeater where you are already full quieting at 5W or 10W level gains you nothing but more expense running the radio due to electricity costs, more RF exposure and bad operating habits.  

You are talking "higher gain antenna" when you are currently using a magmount on a file cabinet.  

At that point, the magmount on a pizza pan up on the roof would prove to be "higher gain" than what you are doing at present.  

And YES, a good antenna mounted where it will "get out" will likely always trump more power!  

The reality here is that you bought more power than you need.  So much power that it is going to prove problematic unless you utilize some common sense and keep the RF level turned down.  Halfway or so should be considered all you will ever need if you put up an antenna.  Save the full 75W for intermittant "emergency" duty.  


KE3WD
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VA7CPC
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« Reply #19 on: August 30, 2007, 10:03:47 PM »

Here's what I did:

Tie a piece of monofilament fishline from the balcony above mine, to my balcony railing.

To that, tie two pieces of 20 gauge magnet wire, each 19 1/2" long.

Presto, an outdoor stealth 2m vertical dipole!

With a 5-watt FT-817, a piece of coax, and two alligator clips (to connect to the magnet wire), I can hit (and hear) all the local repeaters (out to 15-20 miles).

I'd point out that _any_ metal in the walls is going to severly impact an indoor antenna, no matter how much gain it's supposed to have.

   Charles
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WB6BYU
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« Reply #20 on: August 30, 2007, 10:31:31 PM »

How big is your window?  A loop of wire 15" tall and 29" wide, fed with
coax in the middle of one vertical side, gives a pretty good match to
50 ohms and has a little bit of gain over a dipole.  You can stick it to
the inside of the window using suction cups of the kind they sell for
hanging Christmas lights (or just tape.)  You may have to adjust the
dimensions to account for the effects of the glass.  Or you can hang
it on the back of a curtain in front of the window.

Antenna have gain because they focus more energy in some directions
than in others.  A beam of some sort sticking out the window can be
arranged to minimize radiation back into the room, but to some
extent that will depend on the antenna design and the direction you
want to point it in.  Some high-gain yagis can actually radiate more
power in the rear lobe than a dipole, while with others it can be less
by a factor of 10 or more.  If you really are concerned about radiation,
coat the back of your curtains with aluminum foil and use it as a reflector -
that's probably the best you can do for shielding in such a short space.

Certainly use only the amount of power necessary to have a clear signal
into a repeater.  I use 50 watts only in fringe areas.  I leave my home
rig on the 5 watt setting and I can hit plenty of repeaters.


There are lots of possible beam designs, for yagis and quads, plus some
other quirky varieties.  If the antenna has too much gain it will have
to be rotated, though fortunately the beamwidth is wider for vertical
polarization than for horizontal with a yagi.  A short 3-element yagi
can be made easily from a piece of wood or plastic pipe and some copper
wire - all you have to do is to figure out how to mount it.  

As you look around on the web you will find a lot of different designs:
don't feel you have to build any of them exact in all details.  There are
some that have good construction techniques but a poor electrical
design.  Some over emphasize design parameters that realy aren't
of much importance.    In fact, the whole process of choosing a beam
is a matter of trading off a lot of different factors including size, cost,
gain, front-to-back ratio, beamwidth, SWR, SWR bandwidth and feed
method, along with mechanical considerations such as weight, material
availablility, and ruggedness.  So the first step is to consider what
of those are most important to you:  what beamwidth do you need to
cover all (or most) the repeaters and simplex directions of interest?
How practical is it to reach out the window to adjust the direction of the
antenna, vs. leaving it fixed in one place?  What construction methods
are you comfortable with?  What test equipment do you have to get
an antenna tuned up properly?  How can you get the coax back inside
the window?  And what is the building made of?

You may find that a simple dipole spaced out from the side of the
building is adequate for most operation. Or you may need some sort
of beam hinged against the building at the back to allow you to
aim it over 180 degrees to get the repeaters you want (or your friend's
house for simplex.)

But the best advice is try it and see.  We can't know everything about
your building and operating interests - and as a newcomer you may not
know them yet either.  Start with something simple - even the mag
mount on the filing cabinet - and see how well it works.  Then try a
simple vertical hanging in front of the window and see if that is better.
You may find that moving the antenna around inside the room makes
a huge difference - though the optimum location may be different
for different repeaters.  (I knew one family who had an X of masking
tape on their living room carpet - that was where you had to stand
to work a particular repeater with a hand held.)  If that does everything
you want for the moment, fine.  If not, make a list of the places that
need improvement:  perhaps there is one repeater on the opposite
side of the building, in which case you  may end up using one antenna
sticking out each side of the building.

One of the things to learn as a ham is that antennas are never permanent.
They aways can change to better suit your needs.  Don't worry about
having to have everything perfect to start with - until you get some
operating experience you may not even know what type of operating
will interest you most next year.  So start simple and improve things
as you see the need.

Oh, and do keep your power down - good antennas will make far more
difference than raw power output.  And remember that you can't work
a station if you can't hear them (which a good antenna also helps with)
regardless of how much power you run.

If you want some idea how difficult it is to build a beam antenna, check
out the Clear Lake Amateur Radio Club site at www.clarc.org and click
on "articles of interest", then choose "V/UHF Antennas - CHEAP".  That
is one of the best feed designs I have found - simple to build and
works well without needing much adjustment.  (I use PVC pipe for the
boom rather than wood, but that is a minor point.)

Good luck!
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KC2MPG
Member

Posts: 65




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« Reply #21 on: August 31, 2007, 07:32:19 AM »

I found this simle and cheap J Pole on ebay (see link) and was wondering if this could somehow be put out my window on a temporary basis, or simply just leaned against the corner of the room?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110165011961&sspagename=ADME:X:AAQ:US:11
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N3OX
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Posts: 8847


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« Reply #22 on: August 31, 2007, 07:40:46 AM »

I think you'd be better off putting your mag mount out the window or even better, a really light ground plane like this:

http://www.mfjenterprises.com/products.php?prodid=MFJ-1740

A J-pole installed high and in the clear only provides a little increase in performance over a ground plane installed the same way and the thing is, a copper pipe J-pole is kind of heavy.

It probably wouldn't work well inside... NO antenna will work as well inside as outside, so take that as the "take home" message of many our comments here, but a J-pole tends to be extra sensitive to its surroundings as far as tuning goes.

The MFJ ground plane and antennas like it are made entirely of aluminum and will weigh probably a tenth of a 1/2" copper pipe J-pole so it's more likely you could easily safely support it out away from the house on some sort of window mount, and trust me, that's really what you want to do.

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KC2MPG
Member

Posts: 65




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« Reply #23 on: August 31, 2007, 10:08:13 AM »

This looks like its perfect for e, but for 100 bucks its a little pricey:
http://cgi.ebay.com/MFJ-1622-Apartment-Antenna-40-2-Meters-New_W0QQitemZ290155842118QQihZ019QQcategoryZ4672QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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KC2MPG
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Posts: 65




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« Reply #24 on: August 31, 2007, 10:30:28 AM »

Dan, I think I am going to order that MJF groundplane, I may be able to get some sort of temporary mast to stick out the wondow when I want to use it, maybe a short piece of PVC pipe or something.
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DA2KI
Member

Posts: 87




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« Reply #25 on: August 31, 2007, 11:10:39 AM »

In that case, just purchase a SO-239 chassis connector and make your own 2-meter ground plane antenna out of scrap copper house wiring.  Construction is simple and instructions are available from numerious internet web sites.  A good article appears in the ARRL handbook (available at the local library perhaps).

The SO-239 is a UHF-series RF connector.  It is a female chassis connector with a square flange. There are screw holes in each corner of the flange.  You do not want the version that lacks the square flange and just uses a locking nut to hold it in the radio chassis.

The Icom IC-V8000 is a great mobile radio, but the 75-watts output is overkill for your geographical location.  Try the 25, 10, or 5-watt output levels first.  With an outside antenna you should be able to hit all the repeaters that are reachable in your area with 25-watts.  Save the 75-watt output for when you are out West and VHF 2-meter repeaters are far more sparse and separated by long distances.  You will also avoid any front-end overload problems to consumer electronic devices located in other nearby apartments by running a lower output power.
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KE4DRN
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Posts: 3722




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« Reply #26 on: August 31, 2007, 07:54:19 PM »

hi,

take a look at this minimal cost 2m antenna,
half square for 2m

http://www.cebik.com/vhf/hs.html

less then 7" # 12 wire and direct solder to coax
and you are on the air.

easy to hide on a patio or balcony,
even hang in on the wall in the house, dorm or apt.

you will be pleased with the performance.

73 james
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N3OX
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Posts: 8847


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« Reply #27 on: August 31, 2007, 10:20:30 PM »

" Dan, I think I am going to order that MJF groundplane, I may be able to get some sort of temporary mast to stick out the wondow when I want to use it, maybe a short piece of PVC pipe or something.
 "

I think that will work just fine.

Have fun!

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
ONAIR
Member

Posts: 1741




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« Reply #28 on: August 31, 2007, 10:57:02 PM »

    Save yourself some money!  A simple coaxial bazooka vertical dipole hung out your window from a fishing pole or broomstick will work nicely!
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N3OX
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Posts: 8847


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« Reply #29 on: September 01, 2007, 09:11:38 AM »

"A simple coaxial bazooka vertical dipole hung out your window from a fishing pole or broomstick will work nicely!"

What do you like so much about coax bazooka antennas?  If you were building a VHF coax bazooka, presumably you'd be doing it for bandwidth reasons (even though the bandwidth increas is via loss...)

A #12 wire groundplane has 16MHz 2:1 SWR bandwidth around 146MHz!  The MFJ one will have even more.  The SWR is gonna be dummy-load flat across 2m.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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