Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Interaction between buried radials and elevated radiasa  (Read 1710 times)
WB4CMB
Member

Posts: 39




Ignore
« on: January 31, 2013, 09:52:48 PM »

I am interested in experimenting a bit with a vertical/s antenna/s. If I had earlier installed buried radials and then later installed elevated radials, would I see significant interaction?
 Also would like to try a vertical dipole, any problems here? Thanks Ray
Logged
KC4MOP
Member

Posts: 764




Ignore
« Reply #1 on: February 01, 2013, 07:09:54 AM »

Their should not be any interaction. The buried radials are non resonant and are there to reduce the losses in the Earth. You lay out as many and as long as you can.
Elevated radials are TUNED to the band you intend to use on your Vertical. They need to be about 8-15 feet high. Tuning them is not a trick I can share. Someone else might step up and share that one with me too.
The benefit is that you can get away with 8 raised radials TUNED for each band used on that vertical and they are as effective as 60 buried ground radials.
FCC recently allows AM B'cast to use elevated radials cuz of the copper theft of the ground 120ea 120 feet long ground screen mandated by the FCC.
Fred
Logged
W5WSS
Member

Posts: 1782




Ignore
« Reply #2 on: February 01, 2013, 08:33:03 AM »

W8ji is researching the interaction of sets of elevated radials used for multiband verticals.

I used sets of two elevated and sloped radials per band over and under fanned downwards from the antenna base that was suspended at 5ft above ground.

For example the in this case 40m was the lowest band therefore the radials were the longest and were highest followed by the next  band and so on. Each following set being shorter and were directly below was attached to their own insulated anchors in the ground.

The antenna wire sloped upwards almost vertically to a 60ft high point of a tree. I could use any length I wanted with the long rope that dead ended on both ends to the ground

I always held the antenna length to anywhere between 1/4 and 5/8 but the 1/4 wave was easier and matched to the equipment.

The radials were bundled together  at the feed point and traveled away relative to each other until each set reached the ground and attached to an insulated anchor.

Looked like cat whiskers {{{{/i\}}}} parallel to the back of the house (A summer cottage)

I did not evaluate whether or not the radial system altered the antenna pattern, but can say that the radials completed the system and common mode displacement currents reduced to non problematic levels which were problematic before adding them when looking at the antenna wire and feeding as an end fed.

The radials changed the antenna system to balanced center feed and completed it nicely.

W8ji should be posting some more information regarding pattern skewing and multi band radials interactions soon. 73
Logged
W3HKK
Member

Posts: 621




Ignore
« Reply #3 on: February 01, 2013, 10:23:55 AM »

Using a pair of qtr wave  ground planes for  40M, I had all kinds of problems when I  laid radials down at ground level and then horizontally at about 4-7 ft.  Apparently phased arrays are very sensitive to radial field irregularities.

My SWR and antenna radiation patterns would change as I moved the radials.  For example, Id get HUGE signal reports  from 1000-2000 miles away,  and F/B ratios of  30-40 dB, but  much weaker reports from VK/ZL/JA/EU and ZS.  ( they were very difficult to work)   A single GP would outperform the phased array  into these long haul DX areas.

Now Ive  tried to  elevate all 8 radials at about the same level, and have cut them to  1/4 wavelength more carefully.   The PA now works much better on long haul DX than it did before.

I have not individually tuned each radial.

The long haul DX is now much easier to work, even with 100w, and I break pile ups more often than not. 

It's puzzling but that was what I evperience over several years of playing with  2 element phased arrays.
Logged
K3VAT
Member

Posts: 760




Ignore
« Reply #4 on: February 01, 2013, 01:08:11 PM »

I am interested in experimenting a bit with a vertical/s antenna/s. If I had earlier installed buried radials and then later installed elevated radials, would I see significant interaction?
 Also would like to try a vertical dipole, any problems here? Thanks Ray

Fred is essentially correct: one would not expect to see any substantial interaction between the two sets of radials as long as they were not mechanically connected.  In fact, the addition of ground buried radials directly underneath elevated radials should enhance the efficiency of the antenna system that uses elevated Tuned radials.

Vertical dipoles usually do not require radial fields (see N6BT dot COM) and certainly not elevated radials.  The bottom half of the vertical dipole serves as the radial field.  As above, installing buried radials underneath a vertical dipole might enhance your signal in some particular direction and at some particular elevation.

Some of the theory for the above is covered in ON4UN's text, Low-Band DXing and as mentioned by W5WSS Tom's website http://www.w8ji.com/antennas.htm.  The text is worth buying if you're serious about learning antenna theory with LOTS of practical antennas and ideas for the experimenter like yourself.

GL, 73, Rich, K3VAT
« Last Edit: February 01, 2013, 01:11:51 PM by K3VAT » Logged
K3VAT
Member

Posts: 760




Ignore
« Reply #5 on: February 01, 2013, 01:27:50 PM »

Using a pair of qtr wave  ground planes for  40M, I had all kinds of problems when I  laid radials down at ground level and then horizontally at about 4-7 ft.  Apparently phased arrays are very sensitive to radial field irregularities.
<snip>

Yes, phased arrays are indeed sensitive to radial field irregularities.  Each vertical antenna's radial field should be the same, or nearly the same topologically.  That is, if possible, the same number of radials, the same length of those radials, and the installation of a common buss or tie wire mid-way between the two antennas that mutually connects together those radials that would otherwise intersect.  The recommended number of radials per antenna is between 2 and 3 dozen, but some stations have considerably more (50 or 60 or +).  Finally, the wire should be of the same type but this is not as critical as the above 4 points.  This is more or less an ideal situation; compromises can and do occur which may have a minimum impact on performance.

<snip>
My SWR and antenna radiation patterns would change as I moved the radials.  For example, Id get HUGE signal reports  from 1000-2000 miles away,  and F/B ratios of  30-40 dB, but  much weaker reports from VK/ZL/JA/EU and ZS.  ( they were very difficult to work)   A single GP would outperform the phased array  into these long haul DX areas.
<snip>

I suspect that it is due to violations to the above points.  I didn't see what type of feed mechanism you used for your phased array (coax delay, power splitter, hybrid coupler, etc.) so this key component could also be a source of difficulties.  This is confirmed by the fact that a single antenna is outperforming the array (for long haul DX it should be the reverse: the array should win nearly every time).

73, Rich, K3VAT

« Last Edit: February 01, 2013, 01:46:20 PM by K3VAT » Logged
W4VR
Member

Posts: 1198


WWW

Ignore
« Reply #6 on: February 02, 2013, 12:50:38 PM »

You're better of using one or the other.  But, if you use both make sure the elevated radial system is not connected to the ground radials.  I assume you're doing this for testing purposes.  I had 8 elevated radials on 160...I had better luck using a 50 radial system laying on the ground.
Logged
W3HKK
Member

Posts: 621




Ignore
« Reply #7 on: February 02, 2013, 01:19:44 PM »

Ive found using 4 qtr wave radials for a 40m GP with the base elevated at 20 ft worked great for low angle contacts. Back in the  early 70s with a single such GP, I worked KC4USA and the others down there on a regular basis, running phone patches etc. with 150watts.

At the current QTH, with the base of the 40m GP at  heights of between 3 and 7 ft , the elevated radial performance seems more complex and less satisfying.  Im positive  more  height makes it simpler and more effective.

BTW, Im using a Christman feed per ON4UN, with RG-213, accurately cut with an AA-54 antenna analyzer.  ( At first, I used the old MFJ259, but found it wasnt very sharp at identifying the  .25 wavelength points.) 

I read somewhere that a bcst engineer walking under an elevated radial field for an am broadcast station running 10kw found rf was almost undetectable at ground level.  Amazing proof of a well tuned elevated radial system performance!
Logged
WB4CMB
Member

Posts: 39




Ignore
« Reply #8 on: February 03, 2013, 09:26:46 PM »

The vertical I am now building is multiband. I am using seperate elements except maybe using the 40m element for 15m also. It is designed for 40,20,15,10. In its present state it will have the feedpoint for all practical purposes at ground level and I will use radials laying on top of the ground as the ground is now frozen here in CO. I have a wood mast made fm 2 X 3s and 2 X 2s. The lower p/o the mast will have a hole drilled thru so I can pivot the vertical up and down to make it easier to get to when I wish to tune it and/or change things. BTW, I'm trying to dig a hole with a post hole digger, maybe 3 to 3 1/2 ft deep, very difficult but I'll get her done. Took 45 min to get 6 inches with ground frozen. Anyone with good ideas on digging this hole?? I ck'd the rental shop for a motor driven earth auger, $20 hour with 2 hr minimum. Thanks Ray
Logged
W5WSS
Member

Posts: 1782




Ignore
« Reply #9 on: February 04, 2013, 09:04:12 AM »

W3hkk hello, Yes with the system I used, the elevated radial downward slope angle was the angle needed to tether each set tightly to their non conductive anchor at their opposite ends so I did not optimise the slope angle for anything in particular.

I find this subject interesting.

We know that elevated radial system design considerations are relative to feed point impedance and horizontal and vertical radiation where symmetry and balance is desired.

Since the radials when horizontal oriented if symmetrically installed relative to each other than only a remnant of measurable horizontal radiation remains.

Therefore if they elevated radials  are not carefully designed then we get radial their contribution involvement in our system which is understood as destructive and unwanted.

An interesting observation I made when working with such radials and a mobile was when I rotated all the radials evenly around the mobile carbody I was noting noise ingress changes when one radial was near the engine.

I would think that if one designed radials for two over under individual sets of four made of rigid Aluminium like stacking and rotating them each individually could be an interesting new facet to pattern control.

73



Logged
W3HKK
Member

Posts: 621




Ignore
« Reply #10 on: February 04, 2013, 02:12:08 PM »

When I was 14, my  neighbor, an engineer for ATTLongLines, put up a Cushcraft triband ground plane for 20-15-10. It was designed with  four 45 degree sloping radials and resulted in great signals out 1000-2000 miles, but not so great on DX.  The sloping radials improved the match to 1:1 SWR but bumped the radiation angles up to 30-45 degrees or so.  Horizontal radials would have given better DX results but at a somewhat higher SWR ( not a big deal IMO).

Also, with any home made qtr wave  ground plane antenna, using the  radials as guys  makes a lot of sense.  I tie them to polypropylene string. That's sufficient for years of service even in high winds.  A stake in the ground with angle iron, plus some   duct tape ( you must UV shield  the duct tape with black pvc electrical tape orit will fall apart within  1 year) Cheap fiberglas fishing poles ( 20-25 ft long weighing almost nothing and costing $15 each)  fitted inside   surplus fiberglas 1.5" diameter 4 ft mast sections works nicely.  You can also use  pvc pipe but that tends to bend and looks less professional to the neighbors.

Vertical dipoles are great if you have a tall enough support....ie a tree to hang it from. No radials. just coax in the middle  pulled perpendicular away from the antenna causes least  distortion of the field, and is not easy to do.

Logged
W5WSS
Member

Posts: 1782




Ignore
« Reply #11 on: February 04, 2013, 06:03:56 PM »

All good ideas, Take a look at a mobile version I built for 20m phone fullsize 1/4 wave antenna with sloped radials.

The antenna tuned just as expected and was allot of fun.

I am not sure about the toa with that installation but you are probably correct.

The location where the pic was made on a hilltop in Oklahoma see eham at my callsign.

Wb4cmb not to hijack your thread just good conversation
Logged
WB4CMB
Member

Posts: 39




Ignore
« Reply #12 on: February 06, 2013, 09:05:45 PM »

Seems I have the hole digging problem solved.  I added water to bottom of hole.  Frozen dirt was only about 10 in deep.  Then got easier for awhile until about 18 in, then hit hardpack clay.
I would put water in, then wait about 30 minutes.  Did wonders!  I also purchased a small garden "pointed narrow spade".  That made getting the dirt out of the hole and widening the sides much easier.  I'm at 28 in now and there is some sand.  I plan to add a 4 X 4 in this hole, then pour concrete.  I understand concrete makes heat because of the curing process, also there are additives.  Temp was in the 50s today 59 yesterday, cooler, maybe 45 for high tommorow.
Thanks for help!       Ray
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!