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160 meter loading coil




 
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Author Topic: 160 meter loading coil  (Read 6230 times)
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aa5wg
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« on: January 23, 2010, 09:12:48 AM »

Hi to all:
I would like to replace 1/4 wavelength of transmission line with two loading coils.  The band is 160 meters.  I believe this is about 135 feet of ladderline I would like to remove and replace with two loading coils in each leg of the ladderline.

How do I calculate for these two loading coils?
73,
Chuck Pool - AA5WG
Cedar, Michigan
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N2DTS
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« Reply #1 on: January 24, 2010, 12:06:47 AM »

I don't understand the question.
Is the ladder line the antenna?
With a dipole fed with open wire line, you just tune it with the tuner, the only time you need to change the length of the feedline is if you end up at a high voltage or current point I think.

Brett
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aa5wg
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« Reply #2 on: January 24, 2010, 12:59:46 PM »

Brett:
The ladderline goes to an all band doublet.  If I could shorten the ladderline by adding to the tank coil how would you calculate for this
73,

Chuck
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N3DRB The Derb
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« Reply #3 on: January 24, 2010, 01:33:54 PM »

you dont do that. The tank coil is the tank coil. it's not the job of the tank coil to adjust your feedline or antenna to any length.

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Ed/KB1HYS
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« Reply #4 on: January 24, 2010, 02:44:55 PM »

Removing feedline length should not require you to change your tuner.  If your tuner could handle the load initially, it SHOULD be ok with the new length.  You may need to use a series fed configuration to feed the lowest frequency the dipole is cut for, and parallel tune for everything higher as the z will climb with higher frequencies.

Is the dipole resonant on 160? or are you feeding a short antenna?

There are certain lengths feed line that can make it difficult to tune especially if you're using smaller parts or a store-bought feeder and feeding at a voltage node the caps can flashover.  At a current node the coil supports can melt as the darn thing can get HOT. (I lost an MFJ tuna this way, never again) 

Design the tuner to be a resonant tank circuit - able to tune to the lowest design frequency of the system say 1.8 Mhz .  A reasonably sized coil can be made from 1/4 inch copper tubing from the hardware store wound about a 4-inch PVC form. Link couple it to the transmitter.
Use the highest voltage, largest spacing variable cap you can get. A split stator or other isn't required. 

Use any length feed line as required to get to the antenna.  Some bands may require a little additional length to move the input impedance away from a bad spot. 

use clip leads to configure the tuner in either parallel or series and you will be able to tune all bands.
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
aa5wg
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« Reply #5 on: January 24, 2010, 05:27:25 PM »

Hi Derb and Ed:
Thank you for your info.  The antenna is centerfed and is 172 feet long and is uses 450 laddaer line.
Chuck
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Ed/KB1HYS
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« Reply #6 on: January 24, 2010, 09:03:25 PM »

Thats only a little longer than a quarter wave on 160.  You might be able to tune it though, if your feed line is an odd multiple of a quarter wavelength. Don't forget the velocity factor, about 0.88 for the 450 ohm line.   The odd quarter wave feed will transform the low impedance short dipole impedance to some higher impedance and you should (might) be able to parallel feed it with your tuner.
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
aa5wg
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« Reply #7 on: January 25, 2010, 09:20:13 PM »

Ed:
Thank you.
Chuck - AA5WG
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