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 open wire twin feeder for 144 Mhz? 
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Post open wire twin feeder for 144 Mhz?
Whilst employed overseas we had , on a government station, a Marine band transmitter fed via open wire twin feeder into a pair of Yagi antennas phase looped, these covered the north part of the Indian Ocean to listen for pan pan, SOS or other distress signals.

However when I suggest using twin wire feeder for Amateur radio VHF many inform me that this will not work?

What are the proven facts relating to this?

thanks
MM0HDW
I


Sun Oct 30, 2016 1:54 pm
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
Of course it will work, why shouldn't it? I used open wire line on my portable setup for years to a small home made balanced matching unit, it worked fine. It was using 300 Ohm feeder.

It would be interesting to know the reason why it was said it wouldn't work, someones misunderstanding?

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Sun Oct 30, 2016 3:02 pm
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
The only reason it's not used is because all radios are produced with 50 ohm, unbalanced, connections.

The first 2M radio I used, belonging to GW3IKK, was balanced line out/in.
The output stage was an 832 valve, an early version of the QQVO3-20.
Instead of an output link with one side grounded it was a balanced link matched to 300ohm.
Obviously the antenna was suitably matched.
All home constructed, obviously, as there was little manufactured for the higher bands in those days.

The only problem that arises is bringing the feeder into the shack, just as there always is with balanced line.

Cheers

Tony

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Sun Oct 30, 2016 3:57 pm
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
Put the question on QRZ and the result is, to me, unbelievable,. Not at all the results we had on the VHF site for the Indian Ocean where losses were small enough to be disregarded on a run of about 200 feet and I do not see why a balun would be used instead of simple match.
MM0HDW
Typical example on QRZ:-

The reason such line is rarely used at VHF-UHF is because it doesn't work better than coax at those frequencies.
WB2WIK, Nov 17, 2013

Yes, there's "radiation losses" with balanced line at VHF and worse at UHF.

Also, baluns to transform back to 50 Ohms at VHF, and more so at UHF, have loss.

VHF-UHF TV antennas used to all be 300 Ohms balanced and fed with twin lead in the 50-60s-and into the 70s. Then, it all changed to 75 Ohm coax for very good reasons, and it wasn't because coax was cheaper. It was more application appropriate. Coax has less loss than twin lead at UHF, especially if the twin lead gets wet, ice coated, etc. And of course it's much less critical to "run" from one point to another, as it's not impacted by what's around it like balanced line is.
WB2WIK, Nov 18, 2013 #7


Wed Nov 02, 2016 12:46 am
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
Just use expensive, high quality coaxial cable if you want low loss and high performance at VHF, the systems we use are 50 ohm unbalanced so converting that to work with a 300 ohm balanced system will introduce loss and noise.


Wed Nov 02, 2016 7:06 am
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
It will work extremely well if done correctly - much better than any coaxial cable including hardline.
The reason for it not being used by the masses is that it's very fiddly to do, baluns, spacers etc.
There's many successful stations using it even on 70cm with elaborate eme aerial arrays.
Coax is the most hassle free option though.

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Wed Nov 02, 2016 8:20 am
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
F4VPC wrote:
It will work extremely well if done correctly - much better than any coaxial cable including hardline.
The reason for it not being used by the masses is that it's very fiddly to do, baluns, spacers etc.
There's many successful stations using it even on 70cm with elaborate eme aerial arrays.
Coax is the most hassle free option though.

Are the losses from a transformer converting 50 to 300 ohm not greater than a simple common mode choke at the base of the antenna?
Then we have real life installation scenarios where running the feeder will interact with objects?


Wed Nov 02, 2016 9:08 am
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
2E1IIP wrote:
Are the losses from a transformer converting 50 to 300 ohm not greater than a simple common mode choke at the base of the antenna?
Then we have real life installation scenarios where running the feeder will interact with objects?


For a modern day rig using a folded dipole array a Pawsey stub would have to be used to transform from 200 Ohm to 50 Ohm coaxial cable, it makes no difference if the stub is next to the element or at the bottom of the open wire line, I suppose the transformer at the bottom of the line would reduce the length of the coaxial feeder but at the inconvenience of having to rotate the array with the open wire attached, in my portable station that wasn't too much of a problem, if the array is fixed then open wire line is a great option. They isn't too much loss in a Pawsey stub.

It was perfect for my portable operation because at the end of the day it's cheap and if it gets damaged, just put a new piece on.

Also if you've got more than one array they can be phased together using open wire line.

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Wed Nov 02, 2016 10:01 am
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
G4LNA wrote:
2E1IIP wrote:
Are the losses from a transformer converting 50 to 300 ohm not greater than a simple common mode choke at the base of the antenna?
Then we have real life installation scenarios where running the feeder will interact with objects?


For a modern day rig using a folded dipole array a Pawsey stub would have to be used to transform from 200 Ohm to 50 Ohm coaxial cable, it makes no difference if the stub is next to the element or at the bottom of the open wire line, I suppose the transformer at the bottom of the line would reduce the length of the coaxial feeder but at the inconvenience of having to rotate the array with the open wire attached, in my portable station that wasn't too much of a problem, if the array is fixed then open wire line is a great option. They isn't too much loss in a Pawsey stub.

It was perfect for my portable operation because at the end of the day it's cheap and if it gets damaged, just put a new piece on.

Also if you've got more than one array they can be phased together using open wire line.

A lot of VHF/UHF "phasing" used to be done in twin feeder, even if the primary feed was in co-ax, and still is!
Co-ax is convenient, less prone to proximity problems etc., but Twin feeder of suitable impedance, for the job design at hand, will still work very well if suitably installed and employed!

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Wed Nov 02, 2016 6:29 pm
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 open wire twin feeder for 144 Mhz? 
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Post Re: open wire twin feeder for 144 Mhz?
G4LNA wrote:
2E1IIP wrote:
Are the losses from a transformer converting 50 to 300 ohm not greater than a simple common mode choke at the base of the antenna?
Then we have real life installation scenarios where running the feeder will interact with objects?


For a modern day rig using a folded dipole array a Pawsey stub would have to be used to transform from 200 Ohm to 50 Ohm coaxial cable, it makes no difference if the stub is next to the element or at the bottom of the open wire line, I suppose the transformer at the bottom of the line would reduce the length of the coaxial feeder but at the inconvenience of having to rotate the array with the open wire attached, in my portable station that wasn't too much of a problem, if the array is fixed then open wire line is a great option. They isn't too much loss in a Pawsey stub.

It was perfect for my portable operation because at the end of the day it's cheap and if it gets damaged, just put a new piece on.

Also if you've got more than one array they can be phased together using open wire line.


Very true Dave, when I was first licenced and made ZL-specials for 4, 2, & 70cms I used 300ohm twin for the 180 degree phasing sections


Sun Nov 06, 2016 7:54 am
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