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Author Topic: Length of Coax  (Read 388 times)
KA7ZIS
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Posts: 19




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« on: August 01, 2007, 09:46:59 AM »

I'm in the planning stages of a 280' horizontal loop fed with 450 ohm window line to a remote balun fed with coax from the tuner. What is the maximum length of coax to the balun can I use (I need about 30')Also should I cut the window line to any certain wavelength or just put up what I need. I've read it's better to run window line all the way to the tuner but I can't. Thanks and 73.
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W8CAR
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« Reply #1 on: August 01, 2007, 10:15:18 AM »

You need to give us more info. If you are using the loop for all bands the impedance will vary all over the place. If that is the case then cutting the window line to a specific length is not justified. As far as the the balun  goes you don't mention if it's a one to one or step down. The only problem you might have is high voltages(or current) being developed in the balun which depends on frequency, power level and length from load. I would try it and see how it works. Just curious as to why you can't run ladder line all the way?
Dan W8CAR
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WA3SKN
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« Reply #2 on: August 01, 2007, 10:33:50 AM »

This would depend on the wavelength (frequency) you are using.
But, since you are using window line, why don't you run it from the antenna to the tuner and eliminate the coax completely?
That would be the best plan!

-Mike.
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K1BXI
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« Reply #3 on: August 01, 2007, 10:33:50 AM »

Use the length you need to reach the remote balun and no more would be the answer. Then the plot thickens. If your very lucky your tuner will load the system on all the bands. If your remote balun becomes warm to the touch on a particular band then do any tweaking with the loop or 450 ohm feed line. But not knowing the length of 450 ohm line or where you are feeding the loop (corner or somewhere on the side) it's hard to predict what that balun will see on any particle frequency. Just use a good coax, nothing smaller than RG-213 to keep any loss on the higher HF frequency's down and it should work fine. If you are using an amplifier by all means check for any heating on the balun.

Check out W8JI and W4RNL on the web, they have very sound advice on a system like yours............have fun

John
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K5LXP
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« Reply #4 on: August 01, 2007, 11:32:36 AM »

Or, save a bunch of steps and put the tuner at the feedpoint.

Mark K5LXP
Albuquerque, NM
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KA7ZIS
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Posts: 19




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« Reply #5 on: August 01, 2007, 11:49:27 AM »

Some additional information: Yes, this is an all band system and will be fed with approximately 80' of window line. My tuner has a voltage balun while the remote balun is a 1:1 current balun. That's why I'm not running window line to the tuner.
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KA7ZIS
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« Reply #6 on: August 01, 2007, 11:54:38 AM »

Some additional information: Yes, this is an all band system and will be fed with approximately 80' of window line. My tuner has a voltage balun while the remote balun is a 1:1 current balun. That's why I'm not running window line to the tuner. The loop will be fed  3' from the corner.
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KE3WD
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« Reply #7 on: August 01, 2007, 11:54:49 AM »

You could also use two pieces of coax that last run to bring the balanced feed right to you and put the balun right behind the tuner...


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K1BXI
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« Reply #8 on: August 01, 2007, 02:29:35 PM »

If you can get the ladder line direct to the tuner, that is the way to go. That 1:1 current "balun" is just a rf choke it will not change BALance to UNbalance. If bringing the ladder line inside is a problem use KE3WD's suggestion of the double coax. Just be sure to bond the shield at both ends. If you have a problem tuning on a frequency add a short length of either line and try again. Just check the internal balun for heat which is a sign of it getting saturated.

John
 
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N3JBH
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« Reply #9 on: August 01, 2007, 02:52:21 PM »

look at this balaun from array solutions W1JR-50-1

It is a Jerry Sevick, W2FMI copy and should prove to work very good
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N3BIF
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Posts: 1190




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« Reply #10 on: August 01, 2007, 03:44:51 PM »

From MFJ

"To avoid problems matching or feeding any dipole antenna with high impedance lines,
keep the lines around these lengths. The worst possible line lengths are shown in
brackets:
160 meter dipole; 35-60, 170-195 or 210-235 feet.
(Avoid 130, 260 ft)
80 meter dipole; 34-40, 90-102 or 160-172 feet.
(Avoid 66, 135, 190 ft)
40 meter dipole; 42-52, 73-83, 112-123 or 145-155 feet. (Avoid 32, 64, 96, 128 ft)"

 
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WA3SKN
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« Reply #11 on: August 02, 2007, 05:21:33 AM »

If you don't like the voltage balun in the tuner, just put the current balun at the tuner end!  Use balanced line from there to the antenna!

-Mike.
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