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Feeding a 4 bay vertical folded dipole



 
 
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  #1  
Old November 29th 06, 02:01 PM posted to rec.radio.amateur.antenna
n4aeq
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Posts: 14
Default Feeding a 4 bay vertical folded dipole

I need to build a 4 bay folded dipole like the one use on vhf/uhf
repeaters. The folded dipole is easy
enough to figure out but how do you get the 4 - 300ohm dipoles to
combine to one 50ohm feedline,
I have looked close as i can at these and there is no combiner but it
looks like maybe some coax
phasing stubs or lengths of coax inside the antenna support mask?

  #2  
Old November 30th 06, 03:28 AM posted to rec.radio.amateur.antenna
w9gb
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Posts: 134
Default Feeding a 4 bay vertical folded dipole

"N4aeq" wrote in message
ups.com...
I need to build a 4 bay folded dipole like the one use on vhf/uhf
repeaters. The folded dipole is easy
enough to figure out but how do you get the 4 - 300ohm dipoles to
combine to one 50ohm feedline,
I have looked close as i can at these and there is no combiner but it
looks like maybe some coax
phasing stubs or lengths of coax inside the antenna support mask?


The ARRL book, FM and Repeaters (1970s) included information on building a
"phasing harness".

Kevin Custer, K3KKC has some of this information at his Repeater Builder web
site:
http://www.repeater-builder.com/rbti...seddipole.html

w9gb


  #3  
Old November 30th 06, 03:39 AM posted to rec.radio.amateur.antenna
w9gb
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Posts: 134
Default Feeding a 4 bay vertical folded dipole

"N4aeq" wrote in message
ups.com...
I need to build a 4 bay folded dipole like the one use on vhf/uhf
repeaters. The folded dipole is easy
enough to figure out but how do you get the 4 - 300ohm dipoles to
combine to one 50ohm feedline,
I have looked close as i can at these and there is no combiner but it
looks like maybe some coax
phasing stubs or lengths of coax inside the antenna support mask?


Here is a great UHF solution (DB Products commercial 4-bay antenna) -- nice
price
DB Products phasing harness for 4 bay UHF dipole, New in box. 455.0 MHz
center frequency. $50.
http://www.ipass.net/hockaday/com.html

gb


  #4  
Old November 30th 06, 12:59 PM posted to rec.radio.amateur.antenna
Bob Bob
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Posts: 85
Default Feeding a 4 bay vertical folded dipole

There are quite a few possibilities

The first that comes to mind is that 300 ohm ribbon feed from all 4
antennas joined at one point will give you 75 ohms. The ribbons should
be the same length.

You can also use a lower Z line in odd multiples of 1/4 wave to
translate the Z down to a lower value. This is commonly called a Q
section and is worth getting your head into! (you can also translate up
in Z)

You will find that with mast coupling issues the antenna feed Z will
probably be lower than 300 ohms anyway. If for example it gets to 200
ohms a tuned half wave of 300 ohm ribbon on each will translate the same
impedance back to where you combine them. You would then get 50 ohms.

Coaxially you could make a 4:1 balun from 75 or 50 ohm coax. This is a
nice way of feeding 200/300 ohm antennas from coax.

I think in my case I would be concerned what coax/ribbon/joiners/T's etc
I had available for feeding the thing, then work out how to use them..

Cheers Bob

N4aeq wrote:

I need to build a 4 bay folded dipole like the one use on vhf/uhf
repeaters. The folded dipole is easy
enough to figure out but how do you get the 4 - 300ohm dipoles to
combine to one 50ohm feedline,
I have looked close as i can at these and there is no combiner but it
looks like maybe some coax
phasing stubs or lengths of coax inside the antenna support mask?

  #5  
Old November 30th 06, 07:23 PM posted to rec.radio.amateur.antenna
Allodoxaphobia
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Posts: 148
Default Feeding a 4 bay vertical folded dipole

On Wed, 29 Nov 2006 21:28:06 -0600, w9gb wrote:
"N4aeq" wrote in message
ups.com...
I need to build a 4 bay folded dipole like the one use on vhf/uhf
repeaters. The folded dipole is easy
enough to figure out but how do you get the 4 - 300ohm dipoles to
combine to one 50ohm feedline,
I have looked close as i can at these and there is no combiner but it
looks like maybe some coax
phasing stubs or lengths of coax inside the antenna support mask?


The ARRL book, FM and Repeaters (1970s) included information on building a
"phasing harness".


IIRC -- without running down to the ham shack and diggng through my old
copies -- some ARRL Handbook (and/or Antenna Handbook) editions back
then had a complete project description for the whole shee-bang: folded
dipoles, matching/phasing harness, mounting technique(s), etc.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http//jonz.net/ng.htm
  #6  
Old November 30th 06, 07:36 PM posted to rec.radio.amateur.antenna
Cecil Moore
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Posts: 1,614
Default Feeding a 4 bay vertical folded dipole

Allodoxaphobia wrote:
IIRC -- without running down to the ham shack and diggng through my old
copies -- some ARRL Handbook (and/or Antenna Handbook) editions back
then had a complete project description for the whole shee-bang: folded
dipoles, matching/phasing harness, mounting technique(s), etc.


Available on eznec.com, I have used EZNEC in
combination with SIMPFEED.ZIP to design phased
systems that worked well.
--
73, Cecil, http://www.qsl.net/w5dxp
 




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