VK Logger Ham Radio Forum Archive

Once upon a time, when TV installers ran 300 ohm ribbon from the antenna to the TV, they would put a twist in it. This was done to reduce noise pickup in the ribbon. Allegedly.
Which begs the question...What would happen if I put a twist in my 450 ohm open wire line from the antenna to the auto matcher?
I presume it would reduce noise (and signal?) pickup in the line. But what would be the effect on transmit?
If the line was radiating would it create a corkscrew radiation?
Would the line be a continuous current balbal?
Or would it have no effect whatsoever?
Or do I have a twisted mind

Cheers
Nev

Definitely corkscrew radiation!

What I've noticed is when I have a right-hand twist in my open wire feeder I tend to work more right-handed morse operators, and when there is a left-hand twist, I get comms with left-handed operators.

Weird, hey...

Well, Nev, I conclude that you have a twisted mind (otherwise, you wouldn't be in amateur radio ! ).

Twisting the TV ribbon was a (perhaps, valiant) technique to ensure some semblance of balance was maintained in the line (in terms of current in the conductors). The ribbon was often run close to walls, around roof gutters etc, using metal standoffs that had a foot on one end and ring and a bit of plastic through which the ribbon was threaded (I say this for the benefit of those who did not grow up in the 1950s-1960s). This held the ribbon about 6 inches (it was before decimalisation) away from wall/gutter/etc. It's moot as to whether it did the job.

If the ribbon feedline were unbalanced, the feedline would be susceptible to picking up stray signals . . . "noise" . . . if such signals were strong enough, or the line was grossly unbalanced.

What would happen if I put a twist in my 450 ohm open wire line from the antenna to the auto matcher?

Do the experiment and find out, then report your findings here.

The next two questions of yours are the product of your twisted mind.

Looking forward to reading the report/s of your experiment/s.

I use 450ohm ladder line which is twisted to reduce the windage effect from making it flap around (thats why tall chimneys hace a fluted spiral around it) does'nt matter which left or right

Yep, I was going to mention the wind effect too. Putting in a twist stops the flapping.

A bit like putting a twist in ratchet straps when securing a load on a trailer. The twist stops the strap buzzing in the wind.

Thanks all,
It helps to be a little warped.
Roger, I remember those standoffs well.some were better than others.
I am going to replace the homemade feeder with commercial ladderline and the thought about the twist occurred to me.
I suppose if the line was fed correctly it shouldn't radiate.

Good to stimulate the grey matter out there.

Cheers
Nev

The old teaching was that twisting the feeder one turn per yard reduced the radiation from the feed line and as a side benefit reduced wear and tear from flapping.

73

Wayne VK4WDM

I just got the apprentice to twist the 6 inch coax line to stop it flapping
but he let go and it unwound

300 ohm feedline gawd you guys are old and twisted pairs.
The last time I used 300 open line was in 1969 in Goulburn as VK2ZIT using two CH5A austenna stacked yagis.




WDM A yard as in back yard
AH 3 feet one yard 22 yards one chain gawd

Don't forget to use the appropriate direction of twist for the hemisphere you are in, otherwise you might finish up with a higher loss. Something to do with the rotation of the earth.

1. Lay feeder or doubled main line parallel to each other.
Doubled main line is often created with a Bikini Twist for this knot.

2. Wrap doubled end of line around feeder 4 to six times, 10 to 15 times if using braid.

3. Now feed end of feeder through loop at end of doubled line.

4. Pull the double line and feeder in opposite directions to tighten knot.
Note that although the knots were made with the doubled line,
when the knot is pulled tight the feeder will wrap onto the doubled line.




if this sounds a bit fishy its because it is

That's right, VK6ZFG. Otherwise, the Coriolis force will untwist your twisted feedline by one turn every day (rotation of the Earth) and, eventually, it's no longer twisted. If your feedline has 21 twists, this will take 3 weeks.

. . . after which it will begin to twist the feedline in the direction opposite to that it was previously twisted . . .

Come to think of it, if you put 21 twists in your feedline and not care about the direction of the twist, it will self-correct every 3 weeks. Of course, if you only twist it 7 times, it will self-correct every week.

Come to think of it (again), if you don't twist it, you won't have to worry.

Hey Nev, I was thinking this might have applications for the wander lead on the Terlin mobile antenna. wind the wander lead the opposite way to the windings under the gel coat you get noise/signal cancelling, wind it the same way as the windings under the gel coat you might even get some gain... wouldnt that be a good .... I reckon we could market that going by some of the claims I have seen on the "efficiency" of some antennas particularly the ones that list the DX stations they worked as proof it must be efficient... what do you think?

Sorry cant offer any help with the twists in the 450 ohm line etc....

Hi Mike
Just got back from the fang farrier.
What have I started? It just goes to show what idle minds will come up with.
I will be at a daughters place tomorrow from 1800 onwards. Am taking my 2/70 handheld with me. I will see if I can hit Olinda rep. Or Kinglake perhaps. Keep your ears peeled.
She lives at Templestowe.

Catch you later.
Nav

A friend of mine said he had a twisted pair once and found it very painfull.
73 de Mike Vk3KTO

VK2ZRH wrote:Twisting the TV ribbon was a (perhaps, valiant) technique to ensure some semblance of balance was maintained in the line (in terms of current in the conductors).

Yes, an attempt to maintain balance.