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Author Topic: Good comerical made multi band diapole?  (Read 1437 times)
KB6OIN
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Posts: 9




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« on: February 12, 2010, 04:16:25 PM »

Right now I am using a comericaly made muti-band diapole. Its 80-10 meters. I have had it for two years, but it just doesn't tune up on 80 or 15 meters. Anyone out there that can make a recomedation for a multi-band diapole ant? I would be willing to do just a 40-10 meter diapole. My rig is a Yeasu 950 by the way, thanks, Jim
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W5DXP
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Posts: 3639


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« Reply #1 on: February 12, 2010, 05:09:28 PM »

How long is your dipole? What kind and what length is your present transmission line? What kind of balun, if any? What kind of tuner?
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VA7CPC
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Posts: 2414




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« Reply #2 on: February 12, 2010, 06:50:55 PM »

And, just for completeness:

. . . Who made your multiband dipole, and what model is it ?

Without more information, we're just shooting blind.

              Charles
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LA9XNA
Member

Posts: 110




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« Reply #3 on: February 13, 2010, 01:35:23 AM »

Check out this site.
http://www.bushcomm.com/index.php/products/bba
This antenna is made for HAM use and for comercial use.
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K0BG
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Posts: 9899


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« Reply #4 on: February 13, 2010, 04:28:40 AM »

I guess I should ask the obvious; did you try to tune it after you hung it?
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KB2DO
Member

Posts: 53




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« Reply #5 on: February 13, 2010, 07:57:59 AM »

Yes,
I have two recommendations.

1- Buy a copy of the ARRL handbook

2- Find out why ur antenna that u bought 2 years ago
   does not work properly or are u expecting too much
   from what u bought!


73,
robbie
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W4UTI
Member

Posts: 29




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« Reply #6 on: February 13, 2010, 12:41:37 PM »

I am currently using a T2FD antenna (folded dipole) from www.buxcomm.com and it covers 160 - 6 meters and is FLAT across all ham bands. I get very nice reports. They also have an 80 - 6 version. Right away, I'm suspicious of an antenna advertised "for ham or commercial/CB/SWL/etc. use." You have received som excellent advice/questions from the Elmers.

Good luck
73,
Karl W4UTI
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N0AZZ
Member

Posts: 241




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« Reply #7 on: February 14, 2010, 04:49:19 AM »

One word BUCKMASTER spells quilty!
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N4CQR
Member

Posts: 568




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« Reply #8 on: February 14, 2010, 06:40:23 AM »

Ditto, fred's comment above. Damn good investment.

Now, WB2WIK/6 said a while back that he could build one of these in no time and for just a couple of bucks. Maybe you can get him to make you one?

---------
Now if you just want to blow some cash, B&W has a $799.00 dipole that will work 160 through 10.
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KI4SDY
Member

Posts: 1452




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« Reply #9 on: February 14, 2010, 07:20:26 AM »

Find the original instructions for the antenna, either at home or on line. Read them and try to find out what is wrong. If it never did tune up on 80 or 15 meters, then something was not right with the original installation. If it just started doing that, it may be a corrosion or wind damage issue in the antenna or feedline connections.

Here are some simple questions that may help you track down the problem:
How high up is it installed (it may be too low to the ground for 80 meters)? Is it near any metal or other antennas? If it recommends a balun in the feedline, did you install one? What type of feedline was recommended and did you stray from that? Did you try to install cable connectors on the feedline yourself (if so, they may be defective)? Finally, check any exposed connection points for corrosion. If you did not weatherproof them with a sealant, this would be a good time to clean them and do that. Does this antenna have any coils or matching systems that may have gotten waterlogged? If so, dry them out and see if they can be saved or replaced. After checking all of that, if you still have a problem, it could be your tuner, not the antenna.

You probably don't need to spend money on a new antenna. You just need to get this one working correctly. What good would it be to put up another one incorrectly just to get the same results? this is an opportunity for you to get some experience and gain some expertise!
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K1PEK
Member

Posts: 51




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« Reply #10 on: February 14, 2010, 01:13:53 PM »

the Cobra Ultra Lite (different Cobra co. than Cb radios , etc) is an exc multiband ant based on entirely different concept than G5RV's, etc, out there.  See  K1JEK.com     K1JEK, Joe the owner, has put a lot of thought into the quality of his construction.   eham  reviews are strong:  10 pages and without counting there are likely 95% +   5/5 ratings and one I noticed at 4/5 says that it is a great antenna.   A few below the top ratings likely could resolve their matter by revisiting their installation , location, and any non-conforming issues with the antenna.    My company used to sell the best version of a G5RV until Joe's Cobra Ultra Lite came along.  So yes, I have a relationship with Joes' company, but my word and reputation is exc, so they tell me.  Also, I've seen it all, been licensed for 50 years.
73, Steve Davis    K1PEK   DAVIS RF Co.,  Commercial, military, ham: Wire, cable, RF connectors and Cable Design Engineering       www.DavisRF.com
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KI4SDY
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Posts: 1452




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« Reply #11 on: February 15, 2010, 07:23:54 AM »

Warning! Recent posts are not that great for the Cobra Ultra-Light. One recent poster stated that his G5RV out performed it. It looks like another miracle, me too, multi bander antenna. Always be suspicious when a dealer tells you how great his product is.

Again, you need to find out what is wrong with your simple wire antenna before you buy another simple wire antenna and have the same problem. You will probably find that you don't need a new antenna at all. You just need to learn how to install and maintain a wire antenna properly.
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K6AER
Member

Posts: 3535




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« Reply #12 on: February 15, 2010, 08:43:08 AM »

Why not just build a dipole. What is the cost? $10.00

Thirty years ago you could not buy a commercial made ham dipole.

As other have said buy the ARRL handbook and start the journey. This hobby is about learning.
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WB6BYU
Member

Posts: 13576




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« Reply #13 on: February 15, 2010, 10:29:01 AM »

What sort of multi-band antenna are you looking for?

The simplest multi-band design is a doublet of some reasonable length
connected to a tuner in the shack using balanced line.  This gives good
efficiency (as long as the antenna is at least 1/3 wavelength long on
the lowest frequency).  The downside for some people is getting the
ladder line to into the shack and the requirement for a good wide-range
balanced tuner.  Versions where the radiator wire is folded to reduce
the space needed may still work, but often at reduced efficiency.

The next simplest approach is to put multiple dipoles on a common coax
feedline.  When properly adjusted this allows coax feed directly to the
rig without the need for a tuner.  It requires more wires in the air and
more effort to adjust, but offers the best convenience once it is tuned.

There are other designs like the G5RV that use a combination of ladder
line or twinlead for a matching section and coax from there to the rig.
These will usually require a tuner at the rig, and while they do allow
coax feed into the house, losses can be high on some bands where the
coax is not well matched at the antenna.

Another approach is the OCFD, where a single span (usually a half wave
on 80m) is fed off-center to give a plausible feedpoint impedance on
multiple bands.  There are a number of commercial versions and some
designs for homebrew construction.  These give the convenience of
coax feed, but generally will still require a tuner in the shack, may be
prone to RF on the outside of the coax, and may have very high SWR
on some bands (15m is usually a problem.)

A trap dipole gives you direct coax feed and a low SWR on those bands
that the antenna is designed to cover.  It may not cover all the WARC
bands, however, depending on the model.  Some versions that use just
one trap in each side will still require a tuner in the shack on some bands.

There are a number of designs that give a reasonably low SWR across a
wide bandwidth by using resistive loading.  One of the more common is
the T2FD, or resistive-loaded folded dipole, but there are also some
terminated wire designs.  These trade off efficiency for the convenience
of low SWR.  The losses are 5 to 6dB over most of the operating frequency
range, and much worse on lower frequencies where the antenna is less than
about 2/3 wavelength long.  (The common 90' version can be down 10 or more
on 80m.)

If you want a true wide-band design without the losses of resistive loading,
a true fan dipole might be a good choice.  Attach 5 wires each 40' long to each
side of a 4 : 1 balun.  Spread the ends out evenly over a span of 15' to 20'.
SWR should be under 2.5 :1 on all frequencies from 40m through 10m.  (You
won't find these sold for ham use, but there are versions for sale for commercial
or military use, some covering 3 to 30 MHz.)


So the first question to ask is, what are YOUR priorities for an antenna?  Highest
efficiency?  Ability to use it without a tuner?  Are some bands more important
than others?  Is ladder line feed an option you want to consider?  How much space
do you have to put it up?  How much time are you willing to spend tuning it?

Once we know the answers to these questions we can make a reasonable suggestion
for an antenna that will meet your needs.
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K1PEK
Member

Posts: 51




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« Reply #14 on: February 15, 2010, 11:08:57 AM »

Vern, KI4SDI,   ref. your "Warning":  You mention one review that claims a G5RV works better than Cobra.   There are 95 reviews of Cobra on eHam, avg rating is 4.6 out of 5.0.   As you know,  many good products are beat up by hams who don't have the configuration or installation or operating down correctly.  With all due respect to you, and your helpful comments to this requestor in an earlier posting by you,  readers would be better to assess the integrity of the dealer than to subscribe to your (my assumption is perhaps incorrect)  theory to beware of all dealers who tout a product.  In the case of DAVIS RF Co.,  search eHam or elsewhere for  Bury-Flex or Bury Flex , designed by me and you will see numerous comments about our service and integrity...thus I have to comment when you imply that my assessment of Cobra Ultra Lite is biased.  Also, I mentioned in my comment that I stopped selling the top performing G5RV when the Cobra hit the market.... because we only used to sell ONE antenna, a G5RV, just as an ancillary item to our other products. More notably, we do not sell the Cobra only because we decided not to sell any  antenna , and if I was selling it I wouldn't be using eHam Elmer section to promote it.... that's part of my ethics...  We pay eHam for their banner ad service for our company.

   Also,  K1JEK, is straight as an arrow, highly ethical, as I am.  If a ham can't make his Cobra play well, Joe helps him to that end.  

Don't get me wrong, this is not a pissed off answer by any means. I just feel it necessary to respond based on your comment about dealers and in response to  my posting.  I'm very attentive to my belief that one's integrity and ethics are only given or taken by one's self. I try to maintain that personally and business wise.   Based on that, I do have to point out that DAVIS RF does supply the element wire (custom built.. no other antenna uses this closed 3 cond. par'l. design) and the ladder line for the Cobra. I hope that doesn't get us back to "square one" in this discussion.   HI  
   
  Steve Davis,  K1PEK   Davis RF Co.
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