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Author Topic: How can a ground mounted vertical ever work well?  (Read 4851 times)
WD4ELG
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« Reply #15 on: January 14, 2013, 10:16:52 PM »

W8JX, nice pics, nice QTH.  How much better would it work WITH radials?  More efficiency, less loss? 

How much power are you running?
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W8JX
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« Reply #16 on: January 15, 2013, 05:50:43 AM »

W8JX, nice pics, nice QTH.  How much better would it work WITH radials?  More efficiency, less loss? 

How much power are you running?

I usually run 800+ watts (sometimes 1100+) or 50 watts barefoot on 40m. On 20m 50 watts (or less when digital) I do not doubt that radials may improve performance but I might loose some balance too in that higher ground losses allow it too radiate some energy at higher angles for shorter skip.
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KC4MOP
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« Reply #17 on: January 15, 2013, 06:57:42 AM »

Ground conductivity has a lot to do with the magic of the vertical antenna. But we still plan on laying about 40-60 radials as long as we can afford. Barbed wire, steel wire, copper wire, etc. That's why DXpedtions set their stations up by the sea. You can not beat salt water for conductivity.
I use vinyl covered welded fencing that is 4 feet wide and 50 feet long, laying on top of the ground. At the base of the vertical the fencing is bonded together with 2 inch copper straps to the ground rod and shield of the coax from the shack. Great low angle radiator. Good success with S.E. Asia...I'm in Western Pa. 40M and 15M.
Another alternative is elevated radials about 20 feet high and tuned to the band to be used. You can get by with about 8 of them out there and they'll be as effective as 120 radials, 120 feet long laying on the ground. BUT the elevated radials must be tuned to the band used. So multi bands will require more radials up in the air.
Fred
« Last Edit: January 15, 2013, 07:06:26 AM by KC4MOP » Logged
K5LXP
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« Reply #18 on: January 15, 2013, 08:15:47 AM »

You can not beat salt water for conductivity.

Yes you can - with wire.  Metal is *way* more conductive than salt water.

Even the DXpeditions have learned that saltwater is not a substitute for a radial field.  It helps a lot in the far field, but not the EM field immediately surrounding the antenna.

See "Lesson #2"

http://www.k2kw.com/verticals/learning.html


Mark K5LXP
Albuquerque, NM
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W5WSS
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« Reply #19 on: January 15, 2013, 08:45:25 AM »

Has anyone modeled the effects of bending a set of two tuned horizontal elevated radials?

For example, if one needs to turn the direction of the two and keeping them identical.

two radials traveling away from the feed point in opposite directions an equal distance then turning 90 degrees identically then ending.

Symmetry is maintained between the two and length.

The circuit is tuned what happens to the radiation pattern due to the change in direction of the radials?
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WB4SPT
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« Reply #20 on: January 15, 2013, 09:33:49 AM »

Also from K2KW:

Lesson #3: Under most any circumstance, radials should be elevated.

When we first installed the 80m vertical in Jamaica during the ARRL DX Contest, we laid the resonant radials on the ground, believing (as most would) that being on the ocean, etc., that everything would tune up OK and work great. The joke was on us! While tuning the vertical, we were unable to get a proper match. We tried various matching coils, adjusting everything adjustable, all to no avail. The clue we had was that the tuning meter on the MFJ antenna analyzer showed a high value (>50 ohms) even without a matching coil. The antenna should be down in the 20 ohm range, as it is linear loaded and physically short. A full size vertical should be in the low 30 ohm range. When we added a matching coil to the already high VSWR feedpoint, the VSWR got higher! (it should have been lower) All of us glared at N6BT, who is supposed to know everything! Tom did deduce that the radials were obviously coupling into what must be extremely lossy ground (not expected). The interaction with the lossy ground was the single largest factor which impacted the tuning and performance of the vertical antennas.

What to do? Fortunately, Tom had recently read an IEEE article about adding elevated radials to AM broadcast stations that had disintegrating buried radial systems. One of the key points was that the new radials needed to be elevated, not the whole antenna. Actually, the radials can be lifted at an abrupt angle right at the antenna and then run horizontally. We left the vertical in place, but raised the radials around six feet. Immediately we were able to obtain a good match. We concluded that all radials at this location needed to be elevated due to the interaction with the very lossy ground. For the ARRL Contest, we elevated the 160m and 80m radials by around 6 feet, the 40m radials by four feet, and we left the 20m radials sloping from about a foot, down close to the ground. When we returned for the CQ WW CW Contest, we elevated all radials.

When raising the radials, the key is to get them high in as short a horizontal distance as possible, and then run them horizontally. We used two methods: using bamboo poles mounted very close to the vertical to support the radials, we also made loops in the guy ropes to suspend the radials via porcelain insulators.

K2KW has been on other expeditions where he used verticals mounted in the sand, right by the ocean. Many times he said he was unable to achieve a good match. He now knows that the key is to raise the radials.
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RFRY
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« Reply #21 on: January 15, 2013, 11:08:19 AM »

Tom did deduce that the radials were obviously coupling into what must be extremely lossy ground (not expected). The interaction with the lossy ground was the single largest factor which impacted the tuning and performance of the vertical antennas.

How many radials were used when they were lying on the earth, and how long were they in free space wavelengths?

The performance of radial wires lying on the surface of the earth is virtually identical to when they are buried several inches.  In both cases the r-f loss of the radial field is dependent on their number and length.

The link below leads to the experimental results of Brown, Lewis & Epstein in 1937, showing this dependency.  In these tests the radials were buried about 4 inches, in sandy soil in New Jersey (conductivity not better the 4 mS/m).

When using 113 x 0.412-wave radials, the radiation efficiency for monopoles longer than about 50 degrees was only several percent less than a perfect monopole using a perfect ground plane, even for this poor conductivity at the antenna test site.  Radiation efficiency was significantly less for fewer/shorter radials.

http://i62.photobucket.com/albums/h85/rfry-100/BLandERadials.gif
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KF7VXA
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« Reply #22 on: January 15, 2013, 09:06:04 PM »

Should all the radials be for the lowest band. I'm getting a 40-6 meter vertical, from what I understand, all the radials should be for 40 meters even though I intend to do a lot of work on 6 meters. I'll be looking at upgrading to 60-120 meters, but not for a while.
I know I'll need another antenna for that, just want to get my feet wet with an LDG vertical to start with.

I'm also going to put up a 5 element beam for the 6 meters on another pole, but wanted to be able to use the 6 meter on the vertical to hear as much as possible and maybe transmit some also so I know when it's time to turn the house and get the beam pointed right.

New to all of this, I'll be getting my radio next month and antenna the month after and in between upgrading to General.

Great read, thank you so much. I was concerned that much power was lost and little was radiated with the verticals, I now know better as long as the radial system is correct.

Thanks and 73's,  John K
« Last Edit: January 15, 2013, 09:23:05 PM by KF7VXA » Logged
RFRY
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« Reply #23 on: January 16, 2013, 06:14:50 AM »

Should all the radials be for the lowest band. I'm getting a 40-6 meter vertical, from what I understand, all the radials should be for 40 meters even though I intend to do a lot of work on 6 meters. I'll be looking at upgrading to 60-120 meters, but not for a while.

The experiments in 1937 by Brown, Lewis and Epstein show that if only a few buried radials are used (say 15-30), then they can be less than 1/4-wavelength -- because "sparse" radials don't work any better if they are longer than that.

OTOH, when using 90 or more buried radials, system efficiency continues to improve until the radials reach a free-space wavelength of nearly 180o.  For these conditions a Z-matched monopole whose physical height is at least 60o can radiate more than 90% of the applied power -- almost regardless of the conductivity of the earth in which the radials are buried.

« Last Edit: January 16, 2013, 06:17:19 AM by RFRY » Logged
KB6HRT
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« Reply #24 on: January 18, 2013, 09:32:41 PM »

Here is what I did, to make my 43' Vertical work well, Used 3 referenced antennas to work off of, so I had something to compare it to on common bands, covered my back yard with 3000' of radials after I first took reading from the R8 vertical that I had in place before I added the ground radials then after the radials were added then changed out the R8 for my 43' vertical tuned the antenna for the bands I was checking against my reference antennas on same band. I use the 43' vertical on 160-75-and 20 m most of the time it works very well on these bands, compared to the R8 on 20m and very well on 75m at night, in the daytime my inverted Vee outdo the vertical most of the time up to 2000 miles. These have been my findings so far, very happy with the results I have getting using the 43' vertical.............KB6HRT
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