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Author Topic: Amount of radials for Verticals  (Read 9663 times)
WX7G
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Posts: 5973




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« Reply #15 on: November 30, 2012, 05:32:10 PM »

Google N6LF and read the N6LF radial papers. For your antenna thirty 20' radials will do quite well.
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VA3GUY
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Posts: 177




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« Reply #16 on: December 01, 2012, 10:47:00 AM »

A while back, I had a Butternut HF6V vertical.  The Butternut sounded like the best option...especially because there are no traps.  I had it ground mounted in the back yard with only 13 radials of assorted lengths, mounted in a semi-circle (like a half moon...only 180 degrees) just under the surface of the ground and even though the bands haven't been great, generally, if I can hear them, I can work them.   In my opinion, it seems that the radials are not as important as indicated.  Bottom line though, you do what you can with what you've got!
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N3DT
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Posts: 521




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« Reply #17 on: December 01, 2012, 07:28:01 PM »

I'm going to repeat myself here.  I don't know why anyone puts up with ground radials.

Look up C-Pole antenna, get a  ferrite current choke for $20, make the antenna and forget the radials and ground issue, and have a good vertical antenna.

I have one cut for 80M, granted it's rather high, but it works on 160 through 10, but on some bands I also have one cut for 60M and it works on the bands the 80M one doesn't work on, like the higher ones, 17 and 10.

This antenna works great, hung from a tree, black wire, stealth, the wife doesn't see it.

But if you guys want to string all that wire out around your yard and still have a low impedance to feed, go for it.

Believe me there's no reason to play with lossy ground radials.  Verticals are not magic.

Dave
N3DT
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KB4QAA
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Posts: 2332




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« Reply #18 on: December 01, 2012, 09:21:52 PM »

We like our lossy radials to go with our lossy traps and lossy coax.  Wink
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K5LXP
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Posts: 4474


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« Reply #19 on: December 02, 2012, 07:36:41 AM »

Jerry Sevick, W2FMI did a study of short verticals and radials in the late '70's.  10 years ago he released a compilation of these works which you can get from the CQ bookstore.

http://store.cq-amateur-radio.com/Detail.bok?no=105


Mark K5LXP
Albuquerque, NM
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KD4SBY
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Posts: 223




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« Reply #20 on: December 02, 2012, 07:51:18 AM »

Thanks fellows! From the feedback I get the impression that more radials will help, while the length of them is not that important. That is information I can use in my case. As I indicated, there is a limited amount of real estate for radials that I can install, but I did not mention that there are also two big trees in the yard with an extensive root system. That also make radials difficult to install, unless I make them shorter than I want. I will certainly follow up with that and the suggested reading of articles on this subject.

Lets go back to that original post for a second.  'Tuned for the lowest/best SWR?', really?  Okay, but that's just half of tuning an antenna, and not the most important part anyway.  A dummy load has a fantastic SWR but makes for a terrible antenna with without radials...
 - 'Doc

I included that note just to indicate that I did what I was suppose to do with the antenna itself, and there was little in that regard that I could do to improve things

I
A while back, I had a Butternut HF6V vertical.  The Butternut sounded like the best option...especially because there are no traps.  I had it ground mounted in the back yard with only 13 radials of assorted lengths, mounted in a semi-circle (like a half moon...only 180 degrees) just under the surface of the ground and even though the bands haven't been great, generally, if I can hear them, I can work them.   In my opinion, it seems that the radials are not as important as indicated.  Bottom line though, you do what you can with what you've got!

That sounds like my situation as far as radials is concerned! The  problem I have is that I often can hear them, but they can only hear me marginally. They do not get my call completely, for example, or my QTH. It can also be a matter of power, I use 100W, they may use 5 or 6 times that much. But you are right, I just might have to do with what I have!
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NN4RH
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Posts: 318




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« Reply #21 on: December 02, 2012, 09:50:21 AM »

A dummy load has a fantastic SWR but makes for a terrible antenna with ot without radials...


Wouldn't a dummy load make a terrible antenna even with radials?
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NN4RH
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Posts: 318




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« Reply #22 on: December 02, 2012, 09:53:00 AM »

Believe me there's no reason to play with lossy ground radials. 

It's the ground that is lossy, not the radials. Radials reduce the ground losses.
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NN4RH
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Posts: 318




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« Reply #23 on: December 02, 2012, 09:54:50 AM »

Actually it does not even really matter. You can use any length you can fit in.

So radials one foot long would be as good as radials 30 feet long? Sorry. I don't buy that.
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W8JX
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Posts: 5646




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« Reply #24 on: December 02, 2012, 10:30:21 AM »

Actually it does not even really matter. You can use any length you can fit in.

So radials one foot long would be as good as radials 30 feet long? Sorry. I don't buy that.

That is not what I meant. I was referring to fact that they do not need to be resonant when in ground contact. 
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N4NYY
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Posts: 4747




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« Reply #25 on: December 02, 2012, 11:40:52 AM »

Actually it does not even really matter. You can use any length you can fit in.

So radials one foot long would be as good as radials 30 feet long? Sorry. I don't buy that.

Not what he is saying. To be on the safe side, I have heard radials as long as the center radiator. Most people do about 25-35ft lengths all the way around. Some do it longer. Some as big as the space will let them. No one does them 1 foot.
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AC5UP
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Posts: 3835




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« Reply #26 on: December 02, 2012, 12:34:47 PM »

.........you would on a UHF ground plane antenna.
[ D'oh! ]       
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Never change a password on a Friday                
WB6BYU
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Posts: 13143




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« Reply #27 on: December 02, 2012, 01:28:00 PM »

Quote from: KD4SBY

Quote from: W5LZ
Lets go back to that original post for a second.  'Tuned for the lowest/best SWR?', really?  Okay, but that's just half of tuning an antenna, and not the most important part anyway...

I included that note just to indicate that I did what I was suppose to do with the antenna itself, and there was little in that regard that I could do to improve things



Adjusting the antenna for minimum SWR is as good as any other method
of adjusting it, and better than some alternatives.  If the SWR is low then
the system must be close to resonance at that point, since you can't have
a low SWR in a 50 ohm system with high reactance.  And since the reactance
changes with frequency faster than the resistance, the point of minimum
SWR will be very close to resonance.

You'll still find a few misled diehards who insist that you tune it for zero reactance
rather than minimum SWR.  Let's see where that leads...

Let's say we have a 20m vertical with a 5uH loading coil inserted 6' above
the feedpoint, and we are adjusting the length of the upper section above
the coil for resonance at 14.1 MHz.  My EZNEC model suggests a total
length of 11.21 feet, with a input impedance of about 30 ohms or so
depending on the ground loss.  That's tuning the antenna for zero
reactance at the desired frequency:  where is the minimum SWR?  At
14.1225 MHz, if you have a very precise meter.  But the SWR curve is
very flat:  the SWR at resonance is 1.67 : 1, and it is less than 1.7 : 1
from 14.06 to 14.190 MHz.  A shift of 22kHz just isn't going to make
any practical difference in the real world.

But who wants to lay flat on the ground to take measurements right
at the feedpoint?  That's not very comfortable.  So let's say you add
a short coax jumper - say 5' long - between the feedpoint and the
antenna analyzer or SWR meter.  If you tune the antenna for minimum
SWR you get the same reading.  But if you are looking at the reactance
on an SWR analyzer it now looks like +20.7 ohms, even though the SWR
hasn't changed.  Now if you adjust the antenna length or X = 0 you end
up with an antenna length of 10.925 feet, a difference of over 4".  Worse
yet, the SWR at that point is 2.68 : 1.  Why would you want to tune
the antenna to that setting?

Adjusting the antenna for minimum SWR is easy and it works regardless
of the length of coax cable.  Don't believe those who try to tell you
otherwise.
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N4NYY
Member

Posts: 4747




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« Reply #28 on: December 02, 2012, 07:37:22 PM »

.........you would on a UHF ground plane antenna.
[ D'oh! ]       


You are not groundmounting a VHF or UHF antenna.
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K0ZN
Member

Posts: 1544




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« Reply #29 on: December 02, 2012, 07:53:04 PM »

If you have a "low" ( i.e.  near 1:1 SWR) it is because you are losing about 50% of your transmitter output to Ground Losses.  A low SWR shows that
ohmic resistance on the lossy earth ground is ADDING to the antenna radiation resistance and bring up the TOTAL resistance to near 50 ohms, thus
showing a good match for the coax.

Typically, a 1/4 wave ground mounted vertical over a very good, extensive radial system will have a feedpoint of around 36 ohms.....which will give an
SWR of about 1.5 to one. This is the LOWEST SWR you will see if you feed the antenna directly with coax.  Low SWR is NOT always a reliable or accurate
indicator of antenna EFFICIENCY.  To wit:  A typical center fed Zepp will usually have a very high SWR, but the antenna SYSTEM is very efficient if fed
with open wire line or ladderline.

SWR is nothing more than electrical condition that exists on the transmission line.  It can be harmless or bad depending upon the TYPE of transmission line
and the coupling system ("Antenna Tuner") between the transmitter and the line.

In-ground radials do nothing more than reduce ground losses as previous posts note. They are NOT resonant. Simply put: plain old dirt SUCKS as a conductor of RF energy....copper wire conducts very well.....so obviously, you want MOST of your RF power flowing in copper wire and not plain old dirt !

Rough statement:  if you put in about 50 to 60 radials, regardless of length (assuming reasonable length) you will be pleasantly surprised at how well your
antenna will work.

Most of the hams that are unhappy with basic vertical performance don't put in an adequate ground system.  It is just Ohm's Law!!

73,  K0ZN
« Last Edit: December 02, 2012, 07:56:05 PM by K0ZN » Logged
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