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Author Topic: SWR help  (Read 787 times)
KD2BHY
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Posts: 20




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« on: July 19, 2012, 06:14:52 PM »

Hello, I'm a young ham and I just installed a 20 meter dipole. My room is on the top floor so the antenna is right outside my window laid up against the house. Should I feed the coax to the ground then feed it back up the house into my room or just feed it to my rAdio so the coax is horizontal to the ground. Which will give me best performance WITHOUT a tuner



Thanks so much and 73 s


   
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K5LXP
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« Reply #1 on: July 19, 2012, 07:26:19 PM »

Should I feed the coax to the ground then feed it back up the house into my room or just feed it to my rAdio so the coax is horizontal to the ground.

If the horizontal option places the feedline in parallel with one of the dipole elements, then let it droop down a bit so the feedline leaves the feedpoint perpendicular to the elements, and away from the near element.  It wouldn't have to go all the way to the ground.  Using a choke balun or two wouldn't hurt.


Quote
Which will give me best performance WITHOUT a tuner

The one that gets the coax away from the dipole, and the dipole away from the house.  By far the house proximity is going to be most detrimental to performance.


Mark K5LXP
Albuquerque, NM
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KJ4ADN
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Posts: 39




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« Reply #2 on: July 22, 2012, 06:02:15 AM »

Definately get it away from the house, if you can.  Coupling to any parallel metal objects is a problem (in your case).  To prove how well coupling can work to your advantage, look up OMTA antenna, it's a 3 stub vertical, 40-20-15m and only the 40m element is driven.  The 20 & 15m stubs are "RF coupled" by their close relationship to the driven element.  It  could be the wiring just inside the wall of the house!

High SWR...  borrow a meter, and move the antenna around a bit, try it as a sloper and record a few readings - just to see if the length is right.  what you really want to figure out, where is it resonating (hearing the best for the receiver), SWR is going to tell how well the transmitter is matched to the antenna (system).  Try the antenna somewhere away from metal objects and see what the meter says, leave it just a tad long on ... just in case... and then see if you get similar readings back at the house.  That should confirm the antenna is near the target - the thing to keep in mind, "what works at your QTH, might not work at mine."

Beware of cheap coax.   I got a SUPER deal at a HAM fest, 1/2 the price of the stuff I'd used, some knockoff mini 8x stuff - with braid so thin, I could see the white insulation through it.  To be sure, I tried it on several antennas, put the antenna analyzer on it (AIMUHF - not a cheap one), and realized I had come home with a 500' roll of snap-pop-crack coax (it picked up noise from everywhere!).   What was really interesting was when I put in on a known good, properly tuned antenna, the stuff made the antenna look bad?!   So, your antenna could be fine, and just the coax sucks.  Borrow a hunk of coax from someone and see if it looks the same, or works as you expected.

Hope that helps.

KJ4ADN - Bill
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K5KNE
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Posts: 65




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« Reply #3 on: July 22, 2012, 01:28:28 PM »

If you can get the antenna away from the house - the better off you will be. Buildings have a maze of electrical wires to the wall plugs, switches, lights etc.  Often these have a lot of noise on them and if the antenna is close (like in the floor of attic or alongside the metal flashing) - the antenna doesn't work as well as it would out on the clear.

Just try different things and see what seems to work best.  A sure fire answer for one location may not be right for a different location.   

Walter  K5KNE
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