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Re: [TowerTalk] 4 square for 80

To: towertalk@contesting.com
Subject: Re: [TowerTalk] 4 square for 80
From: jimlux <jimlux@earthlink.net>
Date: Sun, 25 Sep 2016 16:00:56 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 9/25/16 11:35 AM, Joe Subich, W4TV wrote:

On 9/25/2016 12:48 PM, jimlux wrote:
One could of course make the transmission lines 3/4 wavelength long,

Which would, in turn, reduce the bandwidth of the cables by a factor
of three

I don't know that the bandwidth is the right term here. Between 3.5 and 4.0, assuming you cut for 3.75, for quarter wave you'd be 84 to 96 degrees, for 3/4 wave, it would be 252 to 288.

For exactly 90 and 270, I at the far end is proportional to E at the near end. As you go away from those, how much does it change - that is, how much "current forcing" do you lose.


and similarly increase losses in the cables which operate at
significant SWR both of which would negatively impact operation of the
4 square on a "wide" band like 80/75 meters.

Do they really have that much loss? I've done the calculations in the past, but I don't remember how much there is. And loss is tricky to calculate when you've got less than a wavelength - the "loss in a transmission line" equation assumes uniform current/voltage along the line, which is not the case here. The voltage losses are small at HF, so the losses come from the current.




73,

   ... Joe, W4TV


On 9/25/2016 12:48 PM, jimlux wrote:
One could of course make the transmission lines 3/4 wavelength long, and
have plenty of length to wrap dozens of turns on however many cores
spaced however frequently along the length of the cable.




On 9/25/16 9:25 AM, Jim Brown wrote:
I see.

73, Jim

On Sun,9/25/2016 5:41 AM, Joe Subich, W4TV wrote:
Jim,

The problem is that, in that application, the cables must be 1/4 wave
long electrically.  That already makes them shorter than desired and
"wound" chokes on each end would shorten them by another 5-7 feet
making the spacing of the 4 square much too small.

On Sun,9/25/2016 6:49 AM, Steve London wrote:

What problem(s) are we attempting to solve with chokes on the 4-square
feedlines ?

Noise.


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