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Author Topic: 160 Meter Radials  (Read 299 times)
K6SI
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Posts: 12




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« on: January 23, 2009, 10:05:10 PM »

I have inverted L for 160 meters. 40 foot vertical run, then 180 foot horizontal run. Question is regarding radials. Am I better off with few, say 6 longer, greater than quarter wave radials, or several, say 12 to 15 shorter, less than quarter wave radials. All radials would be laying on ground, in the grass, and would be insulated number 14 copper wire, house type wire. Have not yet installed radial system. Thanks.
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K0CWO
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« Reply #1 on: January 23, 2009, 10:44:57 PM »

As many as you can put down and as long as you can make them.  The more the better, the longer the better.  They don't have to be a "certain" length for ground radials.  The wire you plan on using will work great.

73, BJ
k0cwo
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K9KJM
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« Reply #2 on: January 24, 2009, 12:17:32 AM »

I agree.   The longer and more the better, But whatever you can get in will help.  As noted, When radials are in or on the ground, There is no point to try to "tune" them to length. (The classic "ideal" length would be just over 1/4 wave long, But whatever you can get in will work lots better than none!)
Also, Do strip the insulation off the wire for in or on the ground use. (They will add to your lightning/safety ground)

If elevated 10 or so feet above ground, Radials can start to be "tuned" to length, Fewer are needed for equal performance, Insulation should be left on for safety, BUT most yards would really become a rats nest of wire with such an installation........
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G3TXQ
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« Reply #3 on: January 24, 2009, 02:46:10 AM »

ARRL: Antenna Book has this to say:

*If you install only 16 radials, they need not be very long - 0.1WL is sufficient.

* If you have the wire, the space and the patience to lay down 120 radials, they should be 0.4WL long. This system will gain about 3dB over the 16-radial case.

* If you install 36 radials that are 0.15WL long, you will lose 1.5dB compared to the 120-radial case.

Note that these Loss figures assume a 0.25WL vertical. Your Inverted L has a much higher radiation resistance (>100 ohms), and therefore its efficiency will be a lot less influenced by the ground system losses.

You should also note that the 220ft total length of your Inverted L is pulling current away from the vertical section and into the horizontal section. That is producing a lot more high-angle radiation at the cost of some low-angle radiation.

73,
Steve
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W8JI
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« Reply #4 on: January 24, 2009, 06:11:53 AM »

Most of the big science to day about radials is all based on models, and it is pretty well known the least accurate part of models is the ground interface or things near the earth.

To avoid all this the best idea is to just lay down as many straight evenly spaced radials as you can, and there is little need to go over 100 feet or so on length on 160 meters.

In practical measurements, not models, there is very little difference with more than 30 radials 100 feet long and 120 radials 250 feet long, less than one dB.

We recently measured a 40 meter 1/4 wave antenna system here and the field strength stopped increasing with about 20-30 radials. It is impossible to measure the performance difference my 1/4 wave 160 verticals with 30-50 100 foot radials and a tower with 100 200 foot long radials.

The best idea is to just install as many radials as you can reasoanbly manage in a straight line evenly spaced, if you can get up to 40-50 radials call it quits.

73 Tom

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W4VR
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« Reply #5 on: January 24, 2009, 02:04:19 PM »

You're better off with 12 to 15 shorter ones...this has been proven by several experts in the field.  Now, I don't know why you need to make your inverted-L 240 feet long.  Cut it to 1/4-wave or 3/8-wave and save the left-over wire for another antenna project.
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G0GQK
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« Reply #6 on: January 24, 2009, 03:02:43 PM »

It is suggested by those who know that more short ones are better than a few long ones, that is why the best option is to bury chicken wire over a large area but for most this isn't practical. For raised counterpoise radials they would be 132 ft long which is the quarter wave.

G0GQK
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W8JI
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« Reply #7 on: January 24, 2009, 03:12:42 PM »

Come on now guys. We all know it depends on how long the short radials area, how many there are, and how long they can be, and if they are elevated or not.

We can't make a general statement like "more short ones are better than a few long ones" unless we know a whole lot about the system.  For example if the radials are above ground or if the soil acts like an insulator, it might be much better to have the radials tuned as 1/4 wave long radials. If they are buried in good conductivity soil, then it might be better to use more of them with shorter lengths.

No one would know without knowing how they will act at his house.


73 Tom
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K9KJM
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« Reply #8 on: January 24, 2009, 10:25:52 PM »

The use of galvanized steel chicken wire is a short term answer at best.  In most any soil around here such wire starts to turn into brown rust in just around one year. In three years it is about all gone.

Chicken wire may last a few years above ground, But IN the ground it has not much of a lifespan.

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K6SI
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« Reply #9 on: January 28, 2009, 10:26:52 PM »

OK ALL..... I have read all comments. Thank you. Decided to put in about 2-30 shorter radials.... and trim the horizontal section of the inverted L to shorter length, keep vertical section at 40 feet. Thanks all again.
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