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Old November 30th 06, 01:59 PM posted to rec.radio.amateur.antenna
Bob Bob Bob Bob is offline
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First recorded activity by RadioBanter: Nov 2006
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?