Vertical ant gain vs No radials
 

My antenna is a Butternut HF6V vertical. This antenna is ground mounted and
has 32 radials, which have been laid on top of the grass. The average length
of the radials is about 30 feet. I operate primarily on 40 meters, and I
seem to receive good signal reports.

Today, I ran into another operator on 40 meters, who told me that I would
get a large signal improvement if I increased the number of radials from the
current 32 to 100 or 120. In fact he said he had seen information on the
SteppIR website (http://www.steppir.com/) that supported his assertion.
Remembering how hard I had worked to install my existing 32 radials, I
responded that the effect of quadrupling my radial count would probably give
only a small increase in gain of less than one dB. Indeed Cebik's website
(http://www.cebik.com/gp/gr.html) seems to support this view with a graphic
titled "Radial Length vs. Number of Radials". If I am interpreting this
graphic correctly, the gain increase from 32 radials to 128 radials is about
0.5 dB.

Any comments would be gratefully received.

John, N9JG

Vertical ant gain vs No radials
 

On Wed, 25 Jan 2006 21:25:50 GMT, "John, N9JG"
wrote:

If I am interpreting this graphic correctly, the gain increase
from 32 radials to 128 radials is about 0.5 dB.

Hi John,

Well, if you read the site closely, there are far more variables
involved than one graph offers a final answer to.

On the other hand, if this graph accurately represents all those
variables converging on your conditions; then, yes, it is a huge
increase as reported. You can, on your next QSO offer to that
operator that it probably will boost your signal one half of an
S-meter needle's width.

73's
Richard Clark, KB7QHC

Vertical ant gain vs No radials
 

Well you always wonder if the guy was trolling me, but I wasn't about to
plan on spending the spring putting in an additional 90 verticals unless
there was the prospect of a reasonable payoff.
-- John

"Richard Clark" wrote in message
...
On Wed, 25 Jan 2006 21:25:50 GMT, "John, N9JG"
wrote:

If I am interpreting this graphic correctly, the gain increase
from 32 radials to 128 radials is about 0.5 dB.

Hi John,

Well, if you read the site closely, there are far more variables
involved than one graph offers a final answer to.

On the other hand, if this graph accurately represents all those
variables converging on your conditions; then, yes, it is a huge
increase as reported. You can, on your next QSO offer to that
operator that it probably will boost your signal one half of an
S-meter needle's width.

73's
Richard Clark, KB7QHC

Vertical ant gain vs No radials
 

CORRECTION - I mean to write 90 radials rather than 90 verticals!!!

"John, N9JG" wrote in message
news:r8TBf.756002$xm3.570205@attbi_s21...
Well you always wonder if the guy was trolling me, but I wasn't about to
plan on spending the spring putting in an additional 90 verticals unless
there was the prospect of a reasonable payoff.
-- John

"Richard Clark" wrote in message
...
On Wed, 25 Jan 2006 21:25:50 GMT, "John, N9JG"
wrote:

If I am interpreting this graphic correctly, the gain increase
from 32 radials to 128 radials is about 0.5 dB.

Hi John,

Well, if you read the site closely, there are far more variables
involved than one graph offers a final answer to.

On the other hand, if this graph accurately represents all those
variables converging on your conditions; then, yes, it is a huge
increase as reported. You can, on your next QSO offer to that
operator that it probably will boost your signal one half of an
S-meter needle's width.

73's
Richard Clark, KB7QHC

Vertical ant gain vs No radials
 

John, N9JG wrote:
My antenna is a Butternut HF6V vertical. This antenna is ground mounted and
has 32 radials, which have been laid on top of the grass. The average length
of the radials is about 30 feet. I operate primarily on 40 meters, and I
seem to receive good signal reports.

Today, I ran into another operator on 40 meters, who told me that I would
get a large signal improvement if I increased the number of radials from the
current 32 to 100 or 120. In fact he said he had seen information on the
SteppIR website (http://www.steppir.com/) that supported his assertion.
Remembering how hard I had worked to install my existing 32 radials, I
responded that the effect of quadrupling my radial count would probably give
only a small increase in gain of less than one dB. Indeed Cebik's website
(http://www.cebik.com/gp/gr.html) seems to support this view with a graphic
titled "Radial Length vs. Number of Radials". If I am interpreting this
graphic correctly, the gain increase from 32 radials to 128 radials is about
0.5 dB.

Any comments would be gratefully received.

John, N9JG


Hi John,

I once had a 30m Vertical ground mounted with 120 radials and it worked
great.. but it work quite well with the 40 or so I had at first also..
the other dynamic that is at work that you hardly ever hear about is
that as you increase the number of radials say from your 32 to approach
100 or so you also need to increase their length so it approaches
1/2wave for each radial.

as a rule of thumb you should keep adding radials until you see no
further change in antenna input impedance. At that point it is not
worth the effort or expense to add more.

73 Dave kc1di

Vertical ant gain vs No radials
 

"John, N9JG" wrote in
news:pdTBf.513451$084.293169@attbi_s22:

CORRECTION - I mean to write 90 radials rather than 90 verticals!!!

Heh heh. There does come a point, though, where more verticals will
achieve the same result at less expense than more radials. I've found that
8 radials of about the same length as antenna height works well, even with
multiband antennas. And a second antenna will recover the gain to the same
level as 120 radials (standard broadcast design), plus providing a
steerable pattern. Coils eat up as much and can be eliminated, or made
smaller with top-loading capacity hats.

Or, for radial-free performance, design it as an end-fed half-wave!

--
Dave Oldridge+
ICQ 1800667

Vertical ant gain vs No radials
 

On Fri, 27 Jan 2006 16:13:29 +0000, kc1di wrote:

[op snipped]
Hi John,

I once had a 30m Vertical ground mounted with 120 radials and it worked
great.. but it work quite well with the 40 or so I had at first also..
the other dynamic that is at work that you hardly ever hear about is
that as you increase the number of radials say from your 32 to approach
100 or so you also need to increase their length so it approaches
1/2wave for each radial.

You hear about it if you read Devoldere's "Low-Band DXing." [g]

He quotes a rule of thumb developed by a fellow member of my DX club,
Eric, N7CL, who says that radial length and number should be such that
the tips are not more than 0.015 lambda apart. So if you use 1/4
lambda radials you need 104 of them to be within 0.1 dB of theoretical
max gain (over average to good ground). Half this number would reduce
the gain by about 1/2 dB.

Of course right above this text in the book is a table that shows for
120 radials the optimum length is 0.5 lambda. So the same book, on
the same page has two different "rules."

Personally, my "rule of thumb" is that the radials need be no longer
than the physical height of the radiator (1/4 lambda) and their
number follow Eric's rule.



as a rule of thumb you should keep adding radials until you see no
further change in antenna input impedance. At that point it is not
worth the effort or expense to add more.

The problem with this is that the derived number is dependent upon the
resolution of the instrumentation. If you can't see a 5 Ohm change,
you quit early. If you can resolve 0.1 Ohm, you keep adding wire,
even though the efficiency improvement will be insignificant.

Vertical ant gain vs No radials
 

Wes Stewart wrote:
On Fri, 27 Jan 2006 16:13:29 +0000, kc1di wrote:

[op snipped]
Hi John,

I once had a 30m Vertical ground mounted with 120 radials and it worked
great.. but it work quite well with the 40 or so I had at first also..
the other dynamic that is at work that you hardly ever hear about is
that as you increase the number of radials say from your 32 to approach
100 or so you also need to increase their length so it approaches
1/2wave for each radial.

You hear about it if you read Devoldere's "Low-Band DXing." [g]

He quotes a rule of thumb developed by a fellow member of my DX club,
Eric, N7CL, who says that radial length and number should be such that
the tips are not more than 0.015 lambda apart. So if you use 1/4
lambda radials you need 104 of them to be within 0.1 dB of theoretical
max gain (over average to good ground). Half this number would reduce
the gain by about 1/2 dB.

Of course right above this text in the book is a table that shows for
120 radials the optimum length is 0.5 lambda. So the same book, on
the same page has two different "rules."

Personally, my "rule of thumb" is that the radials need be no longer
than the physical height of the radiator (1/4 lambda) and their
number follow Eric's rule.


as a rule of thumb you should keep adding radials until you see no
further change in antenna input impedance. At that point it is not
worth the effort or expense to add more.

The problem with this is that the derived number is dependent upon the
resolution of the instrumentation. If you can't see a 5 Ohm change,
you quit early. If you can resolve 0.1 Ohm, you keep adding wire,
even though the efficiency improvement will be insignificant.

some point well take Wes,
73 Dave

Vertical ant gain vs No radials
 

If you have decent soil, 32 radials of the length you specified, will be
quite adequate and adding the number indicated by your friend is just a
waste of effort and money. Here's a relatively simple (if not completely
foolproof) way to tell if you have enough radials:

If you know the theoretical radiation resistance of your vertical over a
perfect ground: measure your current input impedance (at the antenna
feedpoint) with your current number of radials.

You can find the theoretical radiation resistance of your antenna by looking
up short monopoles in the ARRL Antenna handbook...Let's say on 40m, your HF6
is 28 ohms (it's shorter than a full 1/4 wave, so it will be somewhat lower
than the 37 ohms of a perfect quarter wave vertical) The shorter the
radiator, the lower the radiations resistance and you can read it directly
from a graph in the book noted above (or in Devoldre's Low Band
DX'ing...can't recall which) (or you can get it from using one of Reg
Edwards programs). Anywho, let's say it's 37 ohms.

Now you measure the input Z of your configuration. Let's say it measures 39
ohms. Your efficiency is 28/39 or 72%. If it were to measure 35 ohms, your
efficiency would be 80%. You can convert this all to dB loss and you will be
able to see if your current 32 radials are enough to make you happy. I found
26 radials that were 60' long were enough to give me better than 80%
efficiency (actually that number started to happen between 12 and 16
radials, but my soil conditions are very good).

This way, you take most of the theory and speculation out of things. Use an
MFJ-269 or some-such and you can do all the measurements yourself. I'm
betting you will find your efficiency better than 70%...also keep in mind
you have some additional losses from your vertical being a multi-bander, so
the efficiency I'm referring to is based on a single band vertical with no
additional loading/trapping/stubbing losses.

In short:

1. Find out what the Radiation Resistance of your shortened antenna should
be.
2. Measure the input Z at the antenna of your actual antenna/radial field
is.

Divide 1 by 2, convert to percent....a "rule of thumb" measure of efficiency
of your system has been obtained.

If you radial field were perfectly lossless, 1 would equal 2. Every ohm
above the theoretical radiation resistance of your antenna that you measure
is "loss" .

Have fun.

....hasan, N0AN
"John, N9JG" wrote in message
news:y1SBf.755914$xm3.21213@attbi_s21...
My antenna is a Butternut HF6V vertical. This antenna is ground mounted
and has 32 radials, which have been laid on top of the grass. The average
length of the radials is about 30 feet. I operate primarily on 40 meters,
and I seem to receive good signal reports.

Today, I ran into another operator on 40 meters, who told me that I would
get a large signal improvement if I increased the number of radials from
the current 32 to 100 or 120. In fact he said he had seen information on
the SteppIR website (http://www.steppir.com/) that supported his
assertion. Remembering how hard I had worked to install my existing 32
radials, I responded that the effect of quadrupling my radial count would
probably give only a small increase in gain of less than one dB. Indeed
Cebik's website (http://www.cebik.com/gp/gr.html) seems to support this
view with a graphic titled "Radial Length vs. Number of Radials". If I am
interpreting this graphic correctly, the gain increase from 32 radials to
128 radials is about 0.5 dB.

Any comments would be gratefully received.

John, N9JG