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Author Topic: 160 meter vertical  (Read 1314 times)
PA3GVI
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Posts: 23




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« on: January 20, 2010, 01:18:38 AM »

I have build a 26 meter long vertical for 80 and 160 meter.The vertical is 70mm thick for 19.3 meters, then tapers from 35 mm to 10 mm.
I intend to use 4 elevated radials.
With short time to the CQWW160 it would be great if it would work just on 160 meter for now.
there are many articles about how to get this work, use a T-network or just a coil at the base.
Some say a coil at base would work just fine..others dont.
I dont have EZNEC so I would like to hear your thoughts on how to tune this vertical the best way for topband.

Rob/PA3GVI
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W8JI
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« Reply #1 on: January 20, 2010, 01:58:02 AM »

I have build a 26 meter long vertical for 80 and 160 meter.The vertical is 70mm thick for 19.3 meters, then tapers from 35 mm to 10 mm.
I intend to use 4 elevated radials.
With short time to the CQWW160 it would be great if it would work just on 160 meter for now.
there are many articles about how to get this work, use a T-network or just a coil at the base.
Some say a coil at base would work just fine..others dont.
I dont have EZNEC so I would like to hear your thoughts on how to tune this vertical the best way for topband.

Rob/PA3GVI

A good loading coil is always most efficient when compared to a complex network of mixed components. Just be sure the vertical has good base insulation! Voltages can be very high in an efficient coil-loaded antenna.


See you in the test!
Tom
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PA3GVI
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« Reply #2 on: January 20, 2010, 02:19:36 AM »

Hi Tom, thank you for the replay.
We worked several times (2003/2004) when I used to live at the lake and used the full size rectangular loop on 160.
That worked very well but unfortunetly I move to a city with much less space.

About the vertical, so a good wide spaced coil at the base would be fine?
I will try that first when we erase the thing on tuesday!

Hope to see you in the contest, I will use PI4W.

73, Rob
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W9OY
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« Reply #3 on: January 20, 2010, 03:35:49 AM »

If it's mechanically feasible consider center loading your vertical instead of base loading, placing the coil about 60% up from the bottom

73  W9OY
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VR2AX
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Posts: 575




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« Reply #4 on: January 20, 2010, 04:30:15 AM »

Test it against your available ATU before the big day. At full power.

I ran a 1/4 wave vert in  the Dec 1996/Jan1997 tests, tuned with a MFJ 989C atu, it was a near disaster.  The coil in the atu became incandescent, and after some pretty decent contacts, atu gave up the ghost and stopped play.

Good luck.
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W8JI
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« Reply #5 on: January 20, 2010, 05:01:13 AM »

Hi Tom, thank you for the replay.
We worked several times (2003/2004) when I used to live at the lake and used the full size rectangular loop on 160.
That worked very well but unfortunetly I move to a city with much less space.

About the vertical, so a good wide spaced coil at the base would be fine?
I will try that first when we erase the thing on tuesday!

Hope to see you in the contest, I will use PI4W.

73, Rob

Rob,

The only unchanging thing about loading coils is optimum turns spacing is about 1 turn thickness if you can manage that. For coils in bottoms of antenna the length to diameter should be close to 1:1. For coils near the top length to diameter neds to be 4:1 or longer.

I would think you do not want the coil up very high because it narrows bandwidth and mechanically complicates the antenna, although I have done that. I have a coil loaded 43 foot vertical I can take pictures of today and send you. It has a long fiberglass insulator about 5 feet above ground. This way I can access the coil to change frequency. With 1500 watts the voltage across that coil is so high it can arc two inches through the air. It has a 2: 1 SWR bandwidth of about + - 15 kHz. If I would move the coil higher the bandwidth would be narrower and voltage much higher.


Do you have access to the antenna top? Can you run a wire off the top and make it an Inverted L antenna?

Tom
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PA3GVI
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« Reply #6 on: January 20, 2010, 05:05:25 AM »

Thanks for the comments but it's got to be base loaded,there's no other option at the moment.
I don't wanto tune with an ATU in the shack.
Hope to get it resonable well with coil and elevated radials.
If I dont get it working I will extend the vertical with wire to make it a inverted L for the contest...and worry later!

Thank you,

Rob/PA3GVI
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K3STX
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Posts: 956




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« Reply #7 on: January 20, 2010, 05:56:14 AM »

Correct me if I am wrong, but I think the radials have to be resonant 1/4 wavelength if they are elevated. Since you are in the city now, are you sure you have room for 40 meter long elevated radials?

paul
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K0OD
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Posts: 2520




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« Reply #8 on: January 20, 2010, 07:37:32 AM »

"good loading coil is always most efficient when compared to a complex network of mixed components"

But isn't it true that using only a base coil won't bring the SWR down as low as would a mixed network.
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PA3GVI
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Posts: 23




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« Reply #9 on: January 26, 2010, 01:17:09 PM »

Remember my post on Eham last week about the 26 meter long vertical which we put up today?
We could raise the antenna quite easiy with the ginpole .
 
First we messured the antenna with an analyser.
We had 4 elevated radials connected to a pole into the ground.
We found a dip and then radials 'isolated' from ground the dip frequency dropped about 900KHz(dip at +/- 2.4Mhz).
This was without any tuning device.
I had a roller inductor which was in serie between the antenna and ground, a tap was made for tuning and connected to the coax.
This type tuning was found in a W6AOR book and thought it would work.
We could only find a dip around 2.4 MHz, 1:1,5 and 50 ohms.(inductor is 25 centimeter long/diameter is 50 mm/42 windings)
I thought we could bring the resonance frequency down by turning the inductor, but not much happened.
This was on the end of a long day with temp about 5 below zero.
Time is tight as I wanto have it worked for the coming weekend.
Should I have the elevated radials hooked up to the grounding rod as well and what should I do with tuning.
Again, it has to be tuned for resonance at the base,
I am thinking what I could try now?
Any advise?......I hope to have it ready for coming weekend.

Rob/PA3GVI
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N6AJR
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Posts: 9879




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« Reply #10 on: January 27, 2010, 12:05:57 PM »

look at Johns homebrew s setup.  K6MM.com  and under antennas.. cheap, easy and it works.
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N6AJR
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Posts: 9879




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« Reply #11 on: January 27, 2010, 12:05:59 PM »

look at Johns homebrew s setup.  K6MM.com  and under antennas.. cheap, easy and it works.
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N6AJR
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Posts: 9879




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« Reply #12 on: January 27, 2010, 12:06:00 PM »

look at Johns homebrew s setup.  K6MM.com  and under antennas.. cheap, easy and it works.
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N6AJR
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Posts: 9879




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« Reply #13 on: January 27, 2010, 12:06:02 PM »

look at Johns homebrew s setup.  K6MM.com  and under antennas.. cheap, easy and it works.
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K9MRD
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Posts: 331




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« Reply #14 on: January 27, 2010, 12:45:49 PM »

"good loading coil is always most efficient when compared to a complex network of mixed components"

But isn't it true that using only a base coil won't bring the SWR down as low as would a mixed network.

Set the feed point a few turns up from the bottom (cold/grounded) end of the coil and then adjust feed point up/down for min SWR. No other components needed.

Wayne
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