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Author Topic: Radial radial radials  (Read 2372 times)
WA9CFK
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« on: February 25, 2013, 09:05:56 AM »

A couple of months back I strung a 5/8 wave inverted L antenna for 160 meters. Since the ground height is 45 feet I expected just local coverage. It turns out that “local” coverage is solid to about 500 to 700 miles or so, with an occasional DX signal heard. My radial system, from another experiment, is composed of 10 wires, 5 quarter wave pairs for 80m through 10m.

I have been reading about radial systems from several sources including the web and it is enough to make your head swim. When I factor in the lay of the land, cost, and effort, I am thinking of 32 radials up to 100 feet long. But before I tackle this half mile of wire, I have some questions that perhaps the group can answer.

The most important thing to me is; will a better radial system improve my Signal to Noise ratio? I have all the noise I need. Wink

In addition,
•   Is a radial system going to help with my 160 m inverted L. The web info suggests it will.
•   When do you reach diminishing returns? How much improvement is gained with 32 vs. 20 radials?  A 1 db. gain hardly seems worth the effort.
•   On 160m would more 60 foot radials be better than fewer 100 foot radials.

I know that the more radials the better but there is a limit to my funds and ambition.  Grin   


     
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K2DC
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« Reply #1 on: February 25, 2013, 11:09:07 AM »

If you're looking for a 1 dB gain, I doubt you'll get it with 32 radials vs. 20.  And the lengths don't matter that much when they're buried or on the ground.  I don't think there's a magic number for the length, but there's a point of diminishing return there, too.  If you can get them to 1/4 wavelength each, go for it.

73,

Don, K2DC
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W0BTU
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« Reply #2 on: February 25, 2013, 11:22:04 AM »

This might help answer some of your questions:
http://www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html

You bet radials will help your 160m inverted-L. But I doubt if they will help your S/N ratio. A separate receiving antenna will, though.
« Last Edit: February 25, 2013, 11:24:13 AM by W0BTU » Logged

RFRY
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« Reply #3 on: February 25, 2013, 03:59:15 PM »

Below is a link showing r-f currents flowing along various numbers and lengths of buried radials (other conditions the same).

These currents were measured accurately by George H. Brown, Ph.D. et al, of RCA Laboratories in Princeton, NJ.  Their findings were published in the Proceedings of the Institute of Radio Engineers in 1937.

This experimental work was the basis from which the FCC defined the buried radial ground systems/radiation system efficiencies required of US AM broadcast stations up to the present day.

The sum of those currents in the buried radials equals/supplies the current flowing into a base-fed vertical monopole, "Tee," or inverted L.  Maximizing the total r-f current flowing at the common point of the buried radials also maximizes the fields radiated by such antenna systems driven against that set of buried radials.

By inspection of these curves and those in the rest of that I.R.E. publication, it can be seen that when using 30 buried radials, there isn't much point in making them longer than about 0.25 of a free space wavelength.  If using only 15 buried radials then that same effective radial length reduces to less than 0.15 wavelength.

The reason for this is that the r-f currents induced in the earth by radiation from the unburied antenna system conductors encounter high r-f losses at, and just below the surface of the earth as they travel through longer paths in the earth within a 1/2-wave radius of the vertical conductor of such antenna systems just to reach those fewer, buried radials.

OTOH, when using 113 or more buried radials, then their effective length extends beyond 0.37 of a free space wavelength.

The 1937 I.R.E. paper of Dr. Brown et al showed that vertical monopoles of physical heights greater than about 50 degrees radiate groundwave fields when driven against 113 x 0.412-wave buried radials that are within several percent of the maximum, theoretical field possible for that monopole for that applied power, when driven against a perfect (zero loss) ground plane.

http://i62.photobucket.com/albums/h85/rfry-100/BLampEFig7_zps4bd19180.jpg
« Last Edit: February 25, 2013, 04:24:54 PM by RFRY » Logged
W5WSS
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« Reply #4 on: February 25, 2013, 04:07:28 PM »

Well it depends....Relative to noise ingress IF your ground mounted inverted L pushing against a flat ground mounted radial system is completed properly by the radial system then I can say no further radials are required for system balance along with return currents and voltages to the vertical for maximum radiated power.

If the antenna feed point is elevated relative to the mandate of really being RF elevated on 160m like no less than 1/8-1/4 wave of base height(very rarely is this possible to the average ham operator) and you are properly completing the antenna using 4 equidistant elevated sloping or horizontally oriented as a radial system then Noise ingress can be minimal only when everything results in a DC isolated from a earthing connection common to the area around the station  on the bottom ends of the radials in a vertical antenna system.

Noise ingress is a symptom of system unbalance between the equipment the antenna feed point and the immediate RF relative environment unless the RF radial system properly completes the system and satisfies Kirchhoff's Law. There will be a measurable level of system noise caused by the difference of electrical potential between the equipment and the area around the station.

What constitutes system satisfaction depends...but when one is able to evaluate changes effected in receiver noise by connection and disconnection of a radial system and a common earthing rod is when one can know that the RF radial system is incomplete. Because when disconnecting or connecting a earthing system when properly completing the system there should be NO change in noise if there is it is caused by noise ingress. Often signals are strong enough to be heard but swamped by that noise that is NOT atmospheric noise.

Listen for noise changes when connecting and disconnecting a station ground rod if noise worsens isolate the radials from ground and double check.
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W0BTU
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« Reply #5 on: February 25, 2013, 04:49:02 PM »

If you only want to minimize noise --and pull out the weak ones-- forget about "optimizing" the antenna you transmit on. Build a receive antenna (like Beverages or K9AYs). Transmit on the vertically polarized antenna (shunt-fed tower or inverted-L), but listen on the Rx ant. That's what all the especially successful stations on 160 do.

http://www.w0btu.com/Beverage_antennas.html#If_theres_no_room_for_a_Beverage
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NH7O
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« Reply #6 on: February 25, 2013, 05:39:57 PM »

I hope that one of the sources the OP is reading is the material by N6LF, for example:
http://www.antennasbyn6lf.com/2010/03/relation-between-vertical-height-and-radial-length.html

There are more worthwhile articles relevant to this case on his site. The best way to know if you are reaching the area of diminishing returns is to use a field strength meter. Keep adding until you don't see any further increase.
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W0BTU
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« Reply #7 on: February 25, 2013, 06:03:12 PM »

I hope that one of the sources the OP is reading is the material by N6LF

Great advice. N6LF knows what he's talking about. I link to his site from mine.
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K0ZN
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« Reply #8 on: February 25, 2013, 07:21:18 PM »

The cold reality is that there is just a LOT of noise on 160. 1.8Mhz is a bad place in the spectrum for atmospheric noise. Powerline noise in particular is bad on that bad.
Almost impossible to escape it unless you live in very rural area with no power lines. Almost all really serious 160 DX'ers use various/multiple specialized receiving antennas in an attempt to reduce noise pick up and improve S/N. Getting out on 160 is much less of a challenge than hearing and improving the signal to noise ratio. That is just the reality of 160 Meters for most hams.

It is very unlikely that there is much you can do to that inverted L to improve the received signal to noise ratio. Actually dramatically improving the radial system may actually
make local noise pick up slightly worse. Keep in mind that the better your ground wave coverage (which a really good radial system helps with) you will hear more power line noise sources for a longer distance!  A lot of man-made noise is vertically polarized. You *may* find slightly better S/N with a balanced horizontal dipole with a
good effective balun at the feed point and you could also add some ferrite beads on the coax to the shack to further try to reduce pick up of vertically
polarized noise. In my experience, 160 M antennas that work against ground (i.e. have earth ground as literally part of the antenna system) such as verticals and Inverted L's seem to pick up more noise than a dipole that is horizontal and totally isolated from earth ground.....but depending upon the noise sources at/near your QTH this may or may not be true. If you have a lot of power lines or industrial sites in your immediate area the candid fact is you have some real challenges improving S/N on 160.
The downside to a dipole is that is generally does not give low angle radiation on 160 M.

As far as putting more RF into the air, there is no question that a good high power amplifier will help on 160 M, especially if you have some losses in the
antenna system. 2 or 3db of ground loss has much less effect if the transmitter output is 1,500 watts than 100 watts! i.e. If you lose 1/2 of your output (3db)
a 750 watt ERP is still pretty decent vs. a 50 watt ERP on a band with a very high noise floor !

"Welcome to 160 Meters!....."

73,  K0ZN
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KC4MOP
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« Reply #9 on: February 26, 2013, 03:30:34 AM »

The beauty of Amateur radio. Each band has a different flavor and challenge. 160M is my favorite. It can have nice surprises. The DX would be mostly CW. A lot of challenges there with noise. CW the best for gettin' thru
Fred
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KB4QAA
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« Reply #10 on: February 26, 2013, 06:29:28 AM »



The most important thing to me is; will a better radial system improve my Signal to Noise ratio? I have all the noise I need. Wink
No.  The Ether doesn't know the difference between what RF is noise and what is desirable signal.  Improve reception and it all increases.   An Inverted L is a omnidirectional antenna.  If you want to eliminate noise you need to use a directional antenna that receives less well in the direction of noise sources.

Quote
•   Is a radial system going to help with my 160 m inverted L.
Yes.

Quote
•   When do you reach diminishing returns? How much improvement is gained with 32 vs. 20 radials?  A 1 db. gain hardly seems worth the effort.
the radials vs. gain curve is relatively straight from the mid twenties on up to 120
radials.  So, it becomes a matter of effort/sweat and dollars.  IMO, 36 radials is about my upper limit of effort. 

Quote
•   On 160m would more 60 foot radials be better than fewer 100 foot radials.
Tests by N6LF pretty well confirm that it is better to have have More but Shorter radials, vs. Fewer Long radials.   This makes sense when you consider that the density of the RF flux lines a greater the closer to the antenna.
   
Some observations
-Radials longer than 1/2 wl, have very little return for the effort
-Radials on or under the ground do not be tuned/cut for a precise lengths for each band, but for the longest band.  Elevated radials do.
-Radials lengths between 0.2-0.3wl (or approx 0.25wl) give the most bang for the buck.  If nothing else, try to make them equal in length to the height of the antenna.

I too highly recommend the N6LF studies.  Buckets of diamonds there.  Ed LaPorte's antenna engineering book is excellent as well.  It is available in re-print for about $15.

     

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WA9CFK
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« Reply #11 on: February 26, 2013, 01:13:45 PM »

I did not think I was plowing any new ground here. A lot of folks have put a great deal of effort into this band and I appreciate them sharing the information.

I must admit I was taken aback by the noise on the band. I have a 1960’s vintage ARRL Mobile Manual that claims that noise on 160m goes through a minimum compared to 80 meters. It certainly is not the case at my site. Wink

Still there is nothing a Ham likes to do more that tweak and tune, so I will be out there slitting the ground when it thaws. In the meantime I have some more reading to do.  Smiley
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K0ZN
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« Reply #12 on: February 26, 2013, 03:39:19 PM »

160 Meters is a neat band, and often underestimated propagation wise, at least in the winter. I am not a big contest guy, but when the ARRL 160 CW Contest is on I usually participate in it and with a "poor" antenna..... an 80 M dipole fed with ladderline and fed as an end fed wire against ground....and I am always able to work both coasts and all over the country easily and in most years some DX stations....and, again, this is with a pretty crappy antenna, relatively speaking. You will also find there are a lot of other
stations out there with fairly small/compromise antennas but they have USEABLE signals, at least on CW. There is a lot more available on 160 than
most people realize, even with poor antennas. When I get more serious about 160 M is during the solar cycle minimums; it can get surprisingly good and the noise levels drop because a true skip zone develops, killing some of the closer in noise sources. The last very deep solar minimum yielded some really good nighttime propagation on 160, even
for "average" stations without specialized receiving antennas. I worked some amazing DX with just a 1/4 wave Inverted L. My personal take is that you just have to go with the flow.....when we have a lot of spots, the upper HF bands are where it is at and at cycle lows, the time and effort to put up a decent 160 M antenna can be quite rewarding. To me, that kind of dynamic is why this hobby is so interesting.  "Your results may vary...."  To me the "worst part" of 160 (and 80 M too...) is the horrific spring and summer time static levels from thunderstorms. I have seen some legitimate "noise floor" levels of 30 db over S-9 !!  Sobering stuff !!  .... kinda hard to work QRP in those conditions !!  .....chuckle.... When you see that kind of energy on your antenna it makes you think maybe you should put some high power diodes in line and try to run your refrigerator off of the energy from the antenna ~!

73,  K0ZN
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WB3CQM
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« Reply #13 on: March 02, 2013, 02:33:50 PM »

Very interesting reading from every one here. Thanks also for sharing .

160 meter or Top Band  probably is the band I like the most of all. It is very challenging for sure. With that said It is a on going study of antenna and ground systems and operating skills.

I suggest additionally to what has been posted here several books .
DXing on the Edge by K1ZM
Array of Light by N6BT
Low-Band Dxing by ON4UN

The subject of elevated radials has been  posted on TobBand Reflector just this day and some very interesting comments to read.

I have 2 T antenna , one for 80 that is 14 feet above the ground with 2 elevated resonant radials. I do NOT argue that I could improve this with 4 or more radials and or a screen on the floor. But I will say it does seem this antenna is as good as my Big T on 160.

The fact that 80 is not 160 we must consider what does that mean as good ?

When I built my 160 meter transmit antenna I did have lots of great help.

Now then I went through  this radial thing over and over and over and asked every one I could about get to give me their opinion.

This I know . At 65 radials I measured 20 ohms with my meter on the big T.

At 115 radials 130 feet long I have measured 15 ohms at the feed point. This is 13,000 feet of no# 12 copper wire laying under the transmit antenna.

There is no way of knowing how many radials a system needs  unless you make measurements . That is my 2 cents.

How long should the radials be ? I say that depends on the number you plan to use. But I believe on the ground or buried NO LESS than 1/8 wave long should be used. That then according to ON4UN book would be about 52 radials used in a on the ground system. (just for example )

Elevated I would say NO less than 2 and 2-32 is what different people say to use. If I list what I have worked with 2 elevated radials I think it would surprise you.

If I understand the terms correctly Radiation Resistance of the antenna , My 1/8 wave T or 65 foot T vertical should be 12.5 ohms.

Therefor I am within 3 ohms of ground lossless system.

I still get Confused with these terms :: so if I make a statement in error > please correct it some one <

With 100 watts I have worked 115 countries on Top Band in 3 or 4 years. Don't ask me how many I missed due to that fact of running only 100 watts ! But the antenna performs and I am convinced but no real proof . When I hit 65 radials is when better things started to happen for me at MY Location with this antenna.

But it is really  IN the Ground System ! I would like to share a few more things but this post is WAY way to long already . 

I would like to share a story of a op in NC near the ocean with a L and no radials if I had time. Just amazing what he sounded like on Top band.

73 JIM
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