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Author Topic: 2m Beam vs Omni base station antenna question  (Read 2453 times)
KC2TLS
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Posts: 4




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« on: May 03, 2009, 09:34:26 AM »

Greetings....
   I am a relatively new ham, and have been operating just mobile for the past year.  I'm finally started to set up a shack at home (VHF first), and am trying to figure what antenna to put up.  No known restrictions other than "unsightliness" from my wife.  Uses are primarily a few local repeaters, though I would like to see what else is out there with a "real" antenna, and having a good base station for RACES / ARES work as needed (currently a RACES member, and I am hoping we'll get ARES started up soon as well).

I'm torn between a beam (and having to deal with the rotator, etc...) and just putting up something like a Diamond X300a (base station / repeater antenna).

As this will be mounted on top of the house (asphalt shingle roof) I'm also concerned about the radiation patterns (though the attic and bedroom to give quite a bit of space from our "normal" living space).

Right now I'll just be hooking up my HT, but I am on the lookout for a good used VHF rig.

I've searched around a bit and have yet to find any comparisons of a "small" beam (less than 10' perhaps) to a big omni (10' tall perhaps).

Thank you in advance for your time and constructive comments about what may be best for my situation.

73's
Adam
KC2TLS
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K3GM
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Posts: 1791




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« Reply #1 on: May 03, 2009, 11:28:13 AM »

You're always...always going to want an omni antenna.  If this is your first one, I'd go with an omnidirectional antenna like a Comet or Diamond products with the white fiberglass radome.

If you're using an HT or even a 50 watt unit, RF exposure from a roof mounted antenna will not be a problem at 2m and 70cm frequencies.  Remember use only the power necessary to make the connection.
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N1BHH
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Posts: 7




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« Reply #2 on: May 03, 2009, 08:28:57 PM »

I would get both a beam and the omnidirectional antenna. I have done this in the past and had great success. I had a friend I would communicate with on 2 meters simplex every morning using an 8 element beam 15 feet up and pointing in the general direction that he traveled and was able to work him with 10 watts out to around 25 miles. it wasn't a solid signal but with a bit of height I'm sure we could have carried on a solid contact out to about 40 miles.

I only lived in a duplex and couldn't get the antenna up high and it was only up for short periods of time to keep the landlord happy. With rooftop mounting on any average house, you can reach out and have solid contacts for many miles depending upon terrain. I only have at present a mag mount Larsen on the air conditioner at 10 feet and I need to get an antenna up higher to get my Echolink RF link up on a full time basis, something I'm planning to do this summer.

Get an omnidirectional antenna for the initial contact, then aim the beam and have a blast.
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K9KJM
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Posts: 2415




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« Reply #3 on: May 03, 2009, 10:44:21 PM »

The antenna to start out with is the OMNI.   I consider the Diamond X300 a great starter omni antenna.

Put it up as high as possible, Use the lowest loss coax available, And keep the coax run as short as possible.

For most folks, The best coax turns out to be TIMES LMR 400 series coax, As long as your overall length is less than 70 or so feet.

Regular LMR 400 is .79 cents a foot (Or lots less if you buy in quantity)
IF you plan to install a rotor some day for a beam antenna, You might want to plan ahead and get the "Ultra flex" LMR 400 made to go around a rotor. Costs more however.......
(Note: Belden 9913 series coax had MANY BAD versions. A good coax to avoid.)

If you are searching for a good mobil/base FM radio, The Yaesu FT 8800 is a real winner. Dual band and can cross band repeat.

(Other older proven good radios include the Icom 2350, 2710, 2800 series. A few Alinco dual banders were also good, But I dont know the exact model numbers.)
Watch out for the "new" Icom VHF/UHF radios! Overpriced garbage!
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KC2TLS
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Posts: 4




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« Reply #4 on: May 04, 2009, 09:31:58 AM »

Thank you for confirming my suspicions that an omni would be the way to start out.  Looking at the pro ported gain on the small beams it appeared about the same as a big omni.

Radio wise if I can track down a good used 100w full sized VHF rig I may go that route - otherwise I will certainly consider Yaesu, as the mobile I use now is the 8900, and I've had great luck with it, great audio reports, and am now used to how it works.  If I had two I'd have an excuse to get the programming software too.

Thank you all for your thoughts!
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KB1LKR
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Posts: 1898




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« Reply #5 on: May 04, 2009, 09:39:22 AM »

"good used 100w full sized VHF rig..."

FM or weak signal (SSB/CW)? For FM you most likely  want the omni (and if a beam, a vertically polarized one), but if SSB/CW/etc. then likely a horizontally polarized beam, though perhaps a horizontal omni loop, moxon, etc. may also be desired, but not a vertical omni!
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K3GM
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Posts: 1791




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« Reply #6 on: May 04, 2009, 11:26:45 AM »

I wouldn't hesitate recommending you get another FT-8900.  I have one, and asode from those darn menus to wade thru, it's a nice radio.  I use one at home, and have a Comet GP15 6,2, and 70cm antenna.  It's a nice antenna, and is even available with an optional N connector (which I got) at the base of it.
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K7CB
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Posts: 81




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« Reply #7 on: May 04, 2009, 05:07:36 PM »

K9KJM said:
"Watch out for the "new" Icom VHF/UHF radios! Overpriced garbage!"

They may be more expensive but they are far from garbage.  NONE of the Icom radios I've owned has EVER had to go back for repairs.  Meanwhile, my FT-100, FT-8100 and FT-8900 have ALL had to go back at least once.  So, tell us again that Icom is garbage.
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K9KJM
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Posts: 2415




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« Reply #8 on: May 04, 2009, 09:54:50 PM »

OK,  Newer Icom VHF/UHF radios are GARBAGE, Especially compared to older Icom units, And other brand dual band radios.

Check the reviews right here on Eham.

The (Overpriced) Icom 2720H (That I waited well over a year for Icom to finally get to market after it was announced) Turned out to be the biggest loser radio I have ever seen!   Intermod nightmare! I live in a fairly rural area, But even so, That radio could not survive within miles of high power pager systems!
Not to mention the failure rate of its finals.......
The 2720 gets a rating of only 3.3 on the reviews. Pretty crappy. Read the horror stories here:   http://www.eham.net/reviews/detail/2475

The newer Icom 2820H is not much better. See the reviews at only 3.4

AND they changed the memory channel management to a miserable "bubble" memory channel system from the older Icoms that let you easily operate them as two different radios in one box.

We switched to Yaesu FT 8800 dual band radios for our ARES use, And have well over a dozen in the area that ALL work just perfect. NO intermod problems, NO failures of any type.
The FT 8800 gets a rating of 4.5 on Eham reviews.
AND is a LOT less money to buy than the overpriced Icoms.

I have been a real Icom fan for many years.  I hope someday they produce a decent VHF/UHF radio again so I can buy from them. In the meantime I will avoid the crap they are selling right now.
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WB6BYU
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Posts: 13225




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« Reply #9 on: May 06, 2009, 04:25:03 PM »

KC2TLS wrote:
> Looking at the pro ported gain on the small beams it appeared about the same as a big omni.

Either you care comparing a BIG omni with a small beam,
or you are relying on published gain figures that are more
appropriately used for garden fertilizer.

On 2m an omni vertical antenna needs to be about 20' tall
to have 6dB gain over a dipole, regardless of what numbers
the Marketing Department might pull out of their nether
regions.  That is about equivalent to a 3-element yagi on
a 28" long boom.  A 3-element quad or 4-element yagi will
outperform it, and longer beams are easily available to
provide even more gain.  (And such antennas are easy to
build at home.)

A 2m omni vertical antenna around 8' tall will have about
3dB gain over a dipole, and anything with a radiator
length around 36 to 40 inches will have 0dB gain because
it will be, effectively, a dipole, even if fed differently.
This includes J-poles, ground planes, etc.  Doesn't mean
they aren't good antennas, just that they don't have any
gain over a different antenna of similar size.


In my experience I've found the most practical antenna
is the 8' size or similar.  One reason is that the vertical
radiation pattern gets very compressed as the gain is
increased by lengthening the antenna.  (You have to do
that to get omnidirectional gain.)  With a 6dBd vertical
(20' tall) a tilt of 10 degrees will cause the gain to
drop below that of a dipole in some directions.  By
contrast a lower gain antenna will see much less of a
drop, even at higher angles.  (This is why a gain vertical
makes no sense on top of the mast of a sailboat.)  The
taller verticals are also more expensive and require
a heavier duty base to keep them vertical.

Unless you have a tall support already available, putting
a lower gain antenna on a mast so the top is at about
the same height as the higher gain one will give close
to the same performance.  When the base of the antenna
is not at least as high off the ground as the antenna is
tall (such as mounting a 20' antenna on a single story
roof) a lower gain antenna raised to the same top height
may actually outperform the higher gain one because the
average height of radiation is higher.  And height makes
more difference than raw gain on VHF/UHF.


So ignore the manufacturers' gain claims:  the gain of
a properly-designed omni vertical antenna is a direct
function of the radiator length.  By using a lower gain
antenna on a mast (or tower) you can mount a beam
higher up on the same support.  There are plenty of beams
available in the 2 to 15' range that will give more gain
than the highest practical omni vertical antenna, and
again you want to get them up as high in the air as
possible.  Even a simple ground plane or J-pole will
work very well for VHF/UHF coverage if you can get it
up in the air.
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KC2TLS
Member

Posts: 4




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« Reply #10 on: May 06, 2009, 06:07:46 PM »

WOW!  Thank you for the detailed informative reply.  That makes quite a bit of sense.

I will likely stick with an omni for now (and not the largest), but if I get in to SSB I will very likely add a quad loop or mid-sized beam.

I'll be putting it 25-30' up, so it will have some height, but I am in the bottom (and middle) of a large river valley (thankfully it is fairly flat here in the valley (Upper Hudson), and i have a clear view south down towards the Catskills and such).

To those debating radios, in my short time as a ham I've realized that just like anything else, there are good products from "bad" companies, and bad products from 'good" companies, and is very hard to find out which is which.  I have had no trouble with my Yaesu 8900r, but I have also had great luck with a used Icom W32a HT I picked up.  I really wish there were a local store to try before I buy, but there isn't.

Thank you all for your input - it has helped clarify things for me tremendously.  Unfortunately, not I want more antennas:)

73's
KC2TLS
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KF4HOQ
Member

Posts: 47




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« Reply #11 on: May 07, 2009, 07:56:53 PM »

I live in an apartment, and I have a 5 element 2m/440 beam from Elk Antennas.  It's about 2 feet long, and it is built for being portable.  However, I would not hesitate to use it outside in a more permanent situation.  The connection to the mast id made of a PVC T-connector, which means that it can be easily switched between vertical and horizontal polarization.  It's very lightweight...maybe just a couple of pounds, so you could put it on a pole and rotate it by hand very easily.  I have mine connected to my IC-706MkIIG, and I don't have any problems getting into the local repeaters down here in Jacksonville, FL, which is the 1st largest city in the US by land size!

Here's the reviews on eham.net:  http://www.eham.net/reviews/detail/4348
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KM3F
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Posts: 502




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« Reply #12 on: May 08, 2009, 08:26:48 PM »

Given a choice between a vertical single element and a beam type, chose the beam with 3 to 5 elements because the pattern will be fairly broad to the front and still provide gain enough to 'about' double your effective radiated power (3db) as well as allow you to access repeaters at a greater distance.
Another benifit is if there is another repeater on the same frequency, you have a chance to put it's direction and siganl in the beams side null and reduce or eliminate interfere.
Now if this were a 10 element beam then it goes into to much directivity and you would be moving it's direction quite often to access other stations besides being quite long..
Example here: I can't access a repeater at about 70 mile over mountain terain with 6 watts on a small J pole antenna.
With my 5 element home brew located in the same place as the J pole, I can now get into the same repeater with 6 watts and see 3 S units more signal from the repeater.
The beam has  about a 45 degree beam width at it's "3 db down points", so the direction is not all that critical.
Hope this gives you another way of evaluating the decision.
Good luck.
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WB9URN
Member

Posts: 96




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« Reply #13 on: May 09, 2009, 03:03:01 PM »

A couple of bucks, a couple of hours, and you can build a REALLY good omni-directional antenna.
Look at...http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12033

I built one and have no problems with it.

Allen
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ONAIR
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Posts: 1737




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« Reply #14 on: May 27, 2009, 04:21:11 PM »

For fun, just throw up a homebrew end fed vertical coaxial dipole!  Cheap and simple to make, and you'll be surprised how well it works as an omni.  The bucks you save could then be applied to an inexpensive 2m beam!
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