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Another 160m Antenna Question




 
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WA2SQQ
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« on: September 28, 2017, 02:15:01 PM »

Wanted to throw out a question on my 160m antenna.
Iím using a shortened sloper Ė a loading coil to resonate 70 ft of wire, with the coax ground connected to the tower. The feed point height is 50 ft, and the wire comes down on a 45 degree angle. I also have an RF choke on the coax at the feed point.

Iím wondering if I have anything to gain by connecting the coax ground to a ľ wave length of wire (instead of the tower), allowing it to extend down the tower about 45 feet, with the remaining wire strung horizontally about 6 ft off the ground?
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W1ITT
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« Reply #1 on: September 28, 2017, 04:48:50 PM »

Rather than run this "other half of the dipole" down the tower and low along the ground, could you just run it out directly from the feedpoint in the opposite direction from the sloper?
Actually, the "sloper" is often analyzed as a feed system for a vertical antenna, the tower.  My preference would be to put a radial ground system under the tower, although that's usually difficult in the typical residential yard.  Another solution beckons however.
Go to your local farm store and get some mesh fencing of the sort that is bonded at every joint.  I use a 100 foot length of 4 foot wide sheep fence, galvanized steel.  It's laid on the ground and hasn't shown sign of rusting in 7 or 8 years.  A friend used this method, running the fencing in his wife's border garden, covering it with bark mulch and worked a south pacific DXpedition on 160m on the first night out with a similar antenna to what you describe.. There was a Ham Radio article back in the 70s or 80s when Bob Sherwood and someone else made some good impedance measurements using single line and crossed fence wire laid on the ground.  Put it where you can, solder some connecting wires to your tower ground and just don't forget where it is when you take the lawnmower out. Mine is out in the puckerbrush.  The sloper thing on top will give you both high and low angle propagation.
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WA2SQQ
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« Reply #2 on: September 28, 2017, 06:21:22 PM »

The fence idea wonít work as the yard is all landscaped. Decided that Iím going to try my idea and see what happens on the antenna analyzer.
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Steve - K4HX
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« Reply #3 on: September 28, 2017, 07:29:44 PM »

What are you hoping to gain?
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KD6VXI
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« Reply #4 on: September 28, 2017, 07:56:39 PM »

Just move the choke down a quarter wavelength from the feed point.  You'll accomplish the same thing, utilizing the braid as the missing half.

Which, is probably close to what's happening now.  If your tower is any appreciable length vs freq., you'll 'shock excite' the outer braid of the coax.

Should put another choke at the base of the tower.  And a choke at the shack entrance.  This would minimize rf on the outer braid during TX and noise intrusion in rx.

--Shane
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WA2SQQ
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« Reply #5 on: September 29, 2017, 07:11:49 AM »

Looking for any incremental improvement, perhaps in bandwidth. Thatís an interesting idea about moving the choke, and an easy one!
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KD6VXI
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« Reply #6 on: September 29, 2017, 09:17:45 AM »

You'll lose balance, but you can run a pair of counterpoise wires.  One cut for the low end, one for the high end.

If you're going to go that route, you should end up with a W for the swr curve.

--Shane
KD6VXI
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