Engineers - Photo 16b.jpg (0/1)
 

Frank, don't forget to use a 1/4-wave vertical when calculating
efficiency.

I assume you always include the power in the ground wave in the total
power radiated when calculating efficiency.

I think radial length intervals of 0.5 metres will be OK for 100 or
more radials.

Reg,

I have always used the 1/4 wave vertical to calculate efficiency.
Most of my calculations do not include the surface wave. The problem
with including the surface wave is that it is computed over a cylindrical
surface at x meters from the antenna. Technically not a surface, but
rather a vertical line in cylindrical coordinates. The surface is implied
due to the expected symmetry of radiation. In my calculations I have
taken "x" as 200 m, so as to ensure the result is in the far-field at 8 MHz
(nominal 5 wavelengths). I compute the field at 1 m intervals, in the "z"
direction to 200 m. To include the total field I would have to allow z
to approach infinity. Taking these data from the NEC output text file, I
import it to Excel. In Excel I compute the radial distance and elevation
angle to the source. Since my increments are in steps of one meter
I can only approximate integral degree points; removing those points
far from integral degrees. I could employ
linear interpolation, but the field intensity variation is relatively
smooth,
and adds no discernable ripple to the radiation pattern. I then
normalize these data to 1 m to match the spherical data for the
sky wave pattern. At 45 degrees elevation there is very little
ground wave effects, I can then combine the two normalized
sets of data, and numerically integrate over a hemispherical surface.

Sorry to bore you with these details, but just to give an idea of
the tedious steps involved in including the surface wave. To compute
the total radiated sky wave involves a simple command in NEC.
Just the same I can compute the total radiated power at 0.5 m
and 10 m radial lengths as a comparison. At every 0.5 m it would
drive me nuts.

Attempting to model a 100 radial system I continually run into
road blocks. At one point I had a complex matrix with 3.6
million entries. Still I think I have a viable model that needs
just a little refinement. Due to the rotational symmetry of the
structure I can employ methods that greatly reduce run time. The
model that should work will consist of thirty-three 10 cm
radials. At the end of these short radials I connect three 9.9 m
radials for a total of 99 radials. If I run into problems I may
have to reduce the segmentation to 25 cm. What is interesting,
in my preliminary results, is that there is only a 2% improvement
in sky wave total radiated power with 120 radials over 36 radials.

Frank

Engineers - Photo 16b.jpg (0/1)
 

The hell you say. Richard's jpg of VSWR came through quite nicely.

Jim



Put it another way - the rec.radio newsgroups are text only.

Rick K2XT

Engineers - Photo 16b.jpg (0/1)
 

RST Engineering wrote:
The hell you say. Richard's jpg of VSWR came through quite nicely.

Not on my news-server. It appears that some ISP's block
binaries and some do not.
--
73, Cecil http://www.qsl.net/w5dxp

Engineers - Photo 16b.jpg (0/1)
 

Cecil Moore wrote:
RST Engineering wrote:
The hell you say. Richard's jpg of VSWR came through quite nicely.

Not on my news-server. It appears that some ISP's block
binaries and some do not.
--
73, Cecil http://www.qsl.net/w5dxp

Few news servers will handle binaries.

Almost every news reader will automaticaly ASCII encode a binary on
transmission and decode it upon receipt.

That's a bit simplified, but basically how it works.

--
Jim Pennino

Remove .spam.sux to reply.

Engineers - Photo 16b.jpg (0/1)
 

Rick wrote:



In order to post a jpg you would need to essentially convert it to
text. I think a program called uuencode does it.
Then it comes out looking like 15,000 lines of garbage to anyone
reading the articles here. It would make you a lot of enemies faster
than calling CQ on 14336.

Problem with the 336 crowd is that they almost never check before _they_
transmit up or down the band. And if they do check, they wait about 500
milliseconds before they figure the freq is clear. They have lots of
enemies themselves, myself being one. They have a very poor reputation
on 20.

tom
K0TAR

Engineers - Photo 16b.jpg (0/1)
 

"Frank's" wrote
Reg,

I have always used the 1/4 wave vertical to calculate efficiency.
Most of my calculations do not include the surface wave. The
problem
with including the surface wave is that it is computed over a
cylindrical
surface at x meters from the antenna. Technically not a surface,
but
rather a vertical line in cylindrical coordinates. The surface is
implied
due to the expected symmetry of radiation. In my calculations I
have
taken "x" as 200 m, so as to ensure the result is in the far-field
at 8 MHz
(nominal 5 wavelengths). I compute the field at 1 m intervals, in
the "z"
direction to 200 m. To include the total field I would have to
allow z
to approach infinity. Taking these data from the NEC output text
file, I
import it to Excel. In Excel I compute the radial distance and
elevation
angle to the source. Since my increments are in steps of one meter
I can only approximate integral degree points; removing those points
far from integral degrees. I could employ
linear interpolation, but the field intensity variation is
relatively
smooth,
and adds no discernable ripple to the radiation pattern. I then
normalize these data to 1 m to match the spherical data for the
sky wave pattern. At 45 degrees elevation there is very little
ground wave effects, I can then combine the two normalized
sets of data, and numerically integrate over a hemispherical
surface.

Sorry to bore you with these details, but just to give an idea of
the tedious steps involved in including the surface wave. To
compute
the total radiated sky wave involves a simple command in NEC.
Just the same I can compute the total radiated power at 0.5 m
and 10 m radial lengths as a comparison. At every 0.5 m it would
drive me nuts.

Attempting to model a 100 radial system I continually run into
road blocks. At one point I had a complex matrix with 3.6
million entries. Still I think I have a viable model that needs
just a little refinement. Due to the rotational symmetry of the
structure I can employ methods that greatly reduce run time. The
model that should work will consist of thirty-three 10 cm
radials. At the end of these short radials I connect three 9.9 m
radials for a total of 99 radials. If I run into problems I may
have to reduce the segmentation to 25 cm. What is interesting,
in my preliminary results, is that there is only a 2% improvement
in sky wave total radiated power with 120 radials over 36 radials.

Frank
======================================

Frank,

Radiating efficiency is of secondary importance. It does not change
very much with length of radials except at very short lengths.

If computing efficiency involves great labour then do it at infrequent
intervals.

What IS important is the input impedance of a collection of N radials
versus length, frequency and ground characteristics. From which
efficiency can be calculated if required.

I know not, and do not need to know, the details of how you use NEC4.
I think it is safe to assume NEC4 provides reasonably correct answers.

After all, the primary purpose of NEC4 is to generate radiation
patterns from highly suspect input data. And I'm sure approximations
are involved somewhere. When a camel is designed by several
committees in succession, who knows how many humps can appear?

I am about to delete all contents of these threads. I look forward to
seeing a message from "Frank's".
----
Reg, G4FGQ.

Engineers - Photo 16b.jpg (0/1)
 

"Frank's" wrote
What is interesting, in my preliminary results, is that there is
only a 2% improvement in sky wave total radiated power with
120 radials over 36
=====================================
Frank,

If what you are saying is that efficiency is the same for both 36 and
120 radials, then, at least at 8 MHz, B,L&E's findings for LF do not
apply at HF.

Amateurs do not use LF. They use HF.
----
Reg.

Engineers - Photo 16b.jpg (0/1)
 

=====================================
Frank,

If what you are saying is that efficiency is the same for both 36 and
120 radials, then, at least at 8 MHz, B,L&E's findings for LF do not
apply at HF.

Amateurs do not use LF. They use HF.
----
Reg.

You could well be correct Reg. I will get back to B, L & E's paper
and see if I can obtain some correlation between the measurements,
and calculated results At the moment I see 2.5% improvement
between 36 and 99 radials at 8 MHz.

What has also been throwing me off track for a while
was the fact that the input impedance of the 99 radial antenna was less
than than the expected radiation resistance of 36 ohms.
I used this assumption on all my previous
results, so they may have some errors. Applying this technique to the
99 radial antenna would lead to a real resistance component of less than
zero.
Cebik's analysis of buried radial monopoles (www.cebik.com) also
corroborate my findings. Based on the total radiated power, (40% of input)
including surface wave, the radiation resistance is closer to 14 ohms.


Frank

Engineers - Photo 16b.jpg (0/1)
 

What about the Lowfers in the 135 KHz range? I've hear rumors of hams
using those LF frequencies...

Scott



Reg Edwards wrote:

"Frank's" wrote
What is interesting, in my preliminary results, is that there is
only a 2% improvement in sky wave total radiated power with
120 radials over 36

=====================================
Frank,

If what you are saying is that efficiency is the same for both 36 and
120 radials, then, at least at 8 MHz, B,L&E's findings for LF do not
apply at HF.

Amateurs do not use LF. They use HF.
----
Reg.

Engineers - Photo 16b.jpg (0/1)
 

"Reg Edwards" wrote:

If what you are saying is that efficiency is the same for both
36 and 120 radials, then, at least at 8 MHz, B,L&E's findings
for LF do not apply at HF.
__________

The BL&E measurements were made at 3 MHz.