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Author Topic: My Omni is Directional  (Read 1806 times)
KE4VVF
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Posts: 61




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« on: September 14, 2012, 08:06:57 PM »

Bought a Jetstream JTB4 tri-band (6m, 2m, 70cm) antenna.  It has three radials, two the same size and one which is longer and appears to have a loading coil.  The long radial is for 6m.  Had it up a while and then replaced it with a 10m vertical. 

Just installed it again and noticed that 2m repeaters I used to hit easily were weak.  I rotated my vertical (yea, it sounds silly) and found that 2m favors the long radial direction by about S2.  Is this normal?  Will I see similar directionality on the other bands? 

Darn shame if I have to put a rotor on my omni.
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KA4POL
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Posts: 2032




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« Reply #1 on: September 14, 2012, 10:00:16 PM »

I could not find a radiation pattern of the antenna. I'd contact the manufacturer about that. However, those patterns are usually measured without external influences. In your case there  might well be something close by influencing this ideal pattern. You could very well find similar effects on the other frequencies.
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KE4VVF
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« Reply #2 on: September 15, 2012, 06:11:39 AM »

In your case there  might well be something close by influencing this ideal pattern. You could very well find similar effects on the other frequencies.

Unfortunately this antenna is 25' away from any structure and it is at least 35' from the nearest tree.  I have it on a 20' mast set into a socket that is essentially in the middle of my yard.  The mast has only one antenna and is fed with LL400.
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KA4POL
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« Reply #3 on: September 15, 2012, 07:25:03 AM »

You might be receiving reflections from that structure if it is metal. It is easily possible to see interferences especially on higher frequencies where moving just some feet away would improve the situation.
As you described the antenna it is not absolutely symmetrical. So there is also a reason for an unsymmetrical pattern.
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WB2WIK
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« Reply #4 on: September 15, 2012, 05:13:23 PM »

Good luck asking Jetstream about it, as they don't make it.

Jetstream is an importer and the goods come from China.

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KA4POL
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« Reply #5 on: September 15, 2012, 09:52:08 PM »

Oh, now we got the explanation. Asking them could make a great experience.
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