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Message |
    
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 692
Registered: 6-2004
| | Posted on Sunday, August 21, 2005 - 3:31 pm: | 
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Does anyone use a beam without a reflector element - only the driven element and directors? I've often wondered why noone manufacturers an antenna this way because you get the best of both worlds - nearly omnidirectional coverage and gain in one direction.
If you could only put up one antenna then this would be an excellent compromise - especially for local chatting where you don't want to miss out on anything.
Of course if you rely on the rejection offered by the reflector to null interference or another operator nearby you'd still want a traditional beam. |
Road_warrior
Advanced Member
Username: Road_warrior
Post Number: 773
Registered: 7-2004
| | Posted on Monday, August 22, 2005 - 10:41 pm: |
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Never seen anyone running a beam without
the reflector. Interesting thought though. |
Marconi
Intermediate Member
Username: Marconi
Post Number: 437
Registered: 11-2001
| | Posted on Tuesday, August 23, 2005 - 1:07 pm: |
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I had an old Moonraker without a reflector element. I built it as suggested here. I found that even so the antenna showed noticable rejection off the back. I had no way of determining the forward, but other station operators said the antenna showed directional qualities as I rotated away from them. The beam also showed to be directional on RX, so I could not say it would show to be omni without a reflector.
I was not happy with the lack of matching response I was getting with the beam so I was not sure what I had or the results I was seeing.
Eventually I moved the driven element and added a standard reflector element to the back. I still was not happy with the tuning response, it was the same as above. The antenna would not tune above 26.425 no matter what I did. I was never able to determine what the problem was. I was told by several that the MR would only work with a quad loop at the back. I am not convinced of that, but that could be true I suppose.
Thus my work with a no-reflector was not conclusive, but this is what I got when trying it as noted above. I am just not up to experimenting anymore. But, I am still curious about the possibilities. |
Karls357
New member
Username: Karls357
Post Number: 1
Registered: 8-2005
| | Posted on Tuesday, August 23, 2005 - 10:21 pm: |
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hello i need help with what is the best way to set up our class c motor home will a duel antennas be best i would nee at least a 7 ft antenna to get 3 ft above roof line will this be a good ground plane this set up ? thank you karl i will be using a superstar 3900eghp when we travel that i use in my tractor at work but it now has a small radio shack radio in it now . |
Road_warrior
Advanced Member
Username: Road_warrior
Post Number: 778
Registered: 7-2004
| | Posted on Wednesday, August 24, 2005 - 11:31 pm: |
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Karl357
You may want to make a separate post of
your own as more people would see it.
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Slugo4449
Member
Username: Slugo4449
Post Number: 68
Registered: 7-2004
| | Posted on Thursday, February 02, 2006 - 9:50 pm: |
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I have a rotatable dipole up for 6 meters. Just one element. The lobes of the signals are off the sides and the nulls are off the ends.
Marty |
Rldrake
Junior Member
Username: Rldrake
Post Number: 44
Registered: 1-2006
| | Posted on Thursday, February 02, 2006 - 11:20 pm: |
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It's done often. Many "beams" use one or more directors and no reflector. Also, it is not at all uncommon to see "beams" in use with no directors and just the driven element and a reflector. Been so since the 1920's. |
Mikefromms
Advanced Member
Username: Mikefromms
Post Number: 843
Registered: 6-2003
| | Posted on Friday, February 03, 2006 - 8:14 pm: |
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Won't this make the beam bi-directional? It wouldn't be so bad to have outgoing and recieve sigal front and back and rejection on the sides.
mikefromms |
Marconi
Advanced Member
Username: Marconi
Post Number: 584
Registered: 11-2001
| | Posted on Friday, February 03, 2006 - 10:08 pm: |
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That too is what I first though Mike, that such a beam should be bi-directional, but I did not find such to be the case. Since the beam was not performing as I wished regarding the tune, I did not keep it up very long. So further observations might have shead more light on this factor. I will never do it again at my age, but maybe some one will. |
Rldrake
Junior Member
Username: Rldrake
Post Number: 48
Registered: 1-2006
| | Posted on Sunday, February 05, 2006 - 5:06 pm: |
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A "beam" with no reflector is still directional. It exhibits gain towards the front and rejection to the sides. It lacks rear rejection and has less side rejection. The rear has no gain (0db) and behaves as a dipole would. A "beam" with just a reflector, and no directors, offers more gain as it offers rejection to the rear. "Beams" most commonly utilize a reflector and at least one director in order to maximize side and rear rejection...thus to provide "high gain" in the direction of interest and attenuating the unwanted noise from the sides and the rear. |
