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Author Topic: No radials for my vertical antenna ! Any alternative solutions ?  (Read 12570 times)
IW5DWU
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Posts: 35




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« on: May 23, 2010, 12:03:47 AM »

Hi guys,
anyone help me to calculate a good system in place to ground radial vertical antenna, i have not free speace to radial system. A good solution might be to insert the ground iron wire, but could someone clarify how to calculate the size based on the lower frequencies (40m-80m-160m). So much the better ? There is a mathematical / electrical formula ? Thanks to everyone for the advice ....

Greetings

Massimo IW5DWU
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KC3JV
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Posts: 20




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« Reply #1 on: May 23, 2010, 08:36:12 PM »

Massimo:

Look up the Petlowany Antenna.   It is a helical coil made to resonate on the band you want.    You can make one for each band.  Another alternative is to use a capacity hat ( four wires will do ) and a coil and tune them to resonate.   The crossed wires in the form of a cross or "X" should be as large as you can make it.  One end of the coil is connected to the cross or "X" , in the center, and the other serves as the connection for the coax braid.   You will need one for each band.   MFJ uses this technique on one of their verticals.

Mark KC3JV
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IW5DWU
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« Reply #2 on: May 24, 2010, 01:13:02 AM »

Thanks Mark i'm looking through the Internet for dimension coil mostly low band.
Side of the square and total length is my problem  Wink

If you have more for me, pse let me know

Regards

Massimo IW5DWU
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KB8LOG
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« Reply #3 on: May 24, 2010, 06:37:59 AM »

This topic is something I have been struggling with as well. Mark, your suggestion about the capacity hat has raised a few questions for me.

- Does your example equate to top-loading the vertical and then topping the coil with the cap hat?

- You mentioned connecting the base of the vertical to the braid of the coax feed line. I'm still in the process of going through my ARRL antenna handbook, but I was wondering what is the difference between using the braid rather than the inner conductor of the coax?

- Are the capacity hat wires kept horizontal or do they slope downward to the ground?

Over the weekend I built a vertical of my own. Like Massimo, I live in an apartment, so space for radials is quite limited if I put the antenna outside. At least when it is inside I can put some wires down without having them bent too much. But outside, on my ground floor patio, I am basically working on a 9' square of concrete, and am not allowed to go beyond that. There's a deck roughly 10 feet above that I can screw into as well. So it's essentially a 9' to 10' cube.

My vertical is very modular. I wanted to have something I can break down easily and tuck away somewhere indoors. What I wound up doing was using 1" PVC to make vertical segments of 2' and 3' in length. I also made a coil on a 1.5" diameter, 1' long section of PVC. Using some 1' PVC connectors I can put each of the segments or the coil together in any order I wish. The base is also 1" PVC and forms an H shape for support, and in the middle of the H I have a 1' piece pointing upward on which I set the other pieces. Adding a capacity hat would be easy thanks to the modular construction. What I am thinking is adding a very short segment of 1" PVC with 4 wires attached to it, and then running those wires to 4 eye hooks I have screwed into the deck above my patio. That would give me a good 3' to 4' for each wire.

I guess what I didn't realize was that you can substitute a capacity hat in for radials. If that's the case, then the idea is extremely appealing.
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IW5DWU
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« Reply #4 on: May 27, 2010, 08:59:25 AM »

But for my right question :


A good solution might be to insert the ground iron wire, but could someone clarify how to calculate the size based on the lower frequencies (40m-80m-160m). So much the better ? There is a mathematical / electrical formula ? Thanks to everyone for the advice ....


Any solution ?

Thanks
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AA4PB
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« Reply #5 on: May 27, 2010, 09:44:15 AM »

A capacity hat is NOT a substitue for radials. A capacity hat can improve the efficiency of a short vertical by reducing the amount of loading inductance (and thus loss) required to bring it into resonance. It has nothing to do with the requirement for radials. No radials, or a poor radial system, equates to loss in the ground which makes the antenna inefficient (i.e. power consumed as heat instead of being radiated).

Radials, if above ground and thus resonant, need to be 1/4 wavelength long for each band. If they a burried and thus not resonant, use as many as practical, as long as practical up to 1/4 wavelength on the lowest band. More radials is better, even if many of them must be shorter than 1/4 wavelength.
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K4CAV
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« Reply #6 on: May 27, 2010, 07:38:34 PM »

You might find this helpful.

http://www.bencher.com/pdfs/00361ZZV.pdf

http://www.bencher.com/pdfs/00803ZZV.pdf

http://www.steppir.com/pdf/radial%20systems%20for%20vertical%20antennas.pdf
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NG0K
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Posts: 335




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« Reply #7 on: May 30, 2010, 06:24:00 AM »

A ground wire won't help.   But if you can get down 12 to 16 radials in any direction and keep them around 1/10th of a wave length on the lowest band then you might get decent performance.  Making them longer isn't going to help much unless you lay down  at least 25 or 30.   I'm assuming that your ground conductivity is average.   Just lay them out on top of the ground first and see if they help.   In my experience, 160m is tough no matter what you do.   
73 Doug ng0k
« Last Edit: May 30, 2010, 06:27:38 AM by Doug Rathman » Logged

73, Doug - NG0K
WX7G
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Posts: 5917




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« Reply #8 on: May 30, 2010, 10:54:35 AM »

But for my right question :

A good solution might be to insert the ground iron wire, but could someone clarify how to calculate the size based on the lower frequencies (40m-80m-160m). So much the better ? There is a mathematical / electrical formula ? Thanks to everyone for the advice ....

Do you refer to a ground rod with no radials? A metal pipe in the earth? If so, that will work. A ground rod 1 to 3 meters is often used.
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G3RZP
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« Reply #9 on: June 05, 2010, 09:51:43 AM »

I feed my 60 foot tower  as a vertical on 80 and 160 with no radials, just four 4 foot long ground rods into heavy wet clay. I feed it as a folded unipole, top loaded by a 4ele Steppir: the feed impedance is very high so it needs a remotely controlled tuner. Adding radials makes no measurable difference to the feed impedance, and I can't measure current in them. I'm waiting the QSLs for finishing 5BDXCC, and I need some operating time to finish 160m DXCC.

Have a look at folded unipoles. Incidentally, the 'Vertical Antenna Handbook' by Paul Lee, N6PL, published years ago by Cown (CQ Publications) is worth getting if you have chance.
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IW5DWU
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« Reply #10 on: June 13, 2010, 03:37:36 AM »

Thanks in advance to everybody.....my better solution (i have 10x15 foot free space) should be put underground thick iron wires in addition metallic jardin railing.
Do you think should working for low band in addition vertical 33 foot antenna ?

Thanks
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KF7CG
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Posts: 811




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« Reply #11 on: June 13, 2010, 05:09:11 AM »

Alternate solution: This is a commercial antenna and I haven't taken the time to dig up technical data on how to construct homebrew. Use an MFJ-1798; this is an "inverted" vertical with a counterpoise on the top and end loading coils and capacitance hats on the bottom. It must be mounted 6 feet or more above the ground to prevent contact with the active element of capacitance hat spokes.

The bottom end of this antenna has high voltage RF on it when transmitting. A reasonable antenna.

KF7CG
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IW5DWU
Member

Posts: 35




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« Reply #12 on: June 13, 2010, 05:50:52 AM »

I know this antenna, but i have not free space to mount near ground  Angry


Alternate solution: This is a commercial antenna and I haven't taken the time to dig up technical data on how to construct homebrew. Use an MFJ-1798; this is an "inverted" vertical with a counterpoise on the top and end loading coils and capacitance hats on the bottom. It must be mounted 6 feet or more above the ground to prevent contact with the active element of capacitance hat spokes.

The bottom end of this antenna has high voltage RF on it when transmitting. A reasonable antenna.

KF7CG
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WX7G
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« Reply #13 on: June 13, 2010, 08:15:04 AM »

I think you are saying you want to optimize the ground system although you cannot install radials. In this case a large diameter ground rod is the best you can do. You can dig a hole having a large diameter and fill it with salted, moist earth. Then pound in a copper ground rod. Or use four ground rods spaced as far apart as you can get them (1 meter for example) and connect them to the vertical.
« Last Edit: June 20, 2010, 11:43:29 AM by DAVE CUTHBERT » Logged
IW5DWU
Member

Posts: 35




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« Reply #14 on: June 20, 2010, 01:59:22 AM »

Thanks guys, i'm waiting fot alternative solutions too,

73s to all
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