Length & number of radials
 

hasan schiers wrote:

I wondered if I could EVALUATE the effectiveness of the 80m inverted L
on 40m as a half wave, by temporarily taking an antenna tuner with wide
range (T-network matches almost anything) out to the feedpoint and
matching it there. If it hears well, and works ok at 300w (tuner
limit), then it might be worth investing in the coil/cap/relays to
switch a more standard high-Z feed in and out. What do you think?

The configuration of 35ft vertical + 35ft (or so) horizontal worked well
for me on 40m at the old QTH, and was quite effective on 80m DX. For
160m, I added a 100ft loading wire to bring the total length up to about
130ft, and that configuration doubled as an end-fed half-wave for 80m
short-skip.

Having a QRO auto-ATU made band changing easy, so it wasn't necessary to
resonate the antenna on any band. However, the quarter-wave resonances
on 80m and 160m could have been trimmed to length.

Coming back to the difference between the 40m vertical quarter-wave and
the bent half-wave, I compared the bare 35ft mast and the same mast with
the added loading wire and didn't find much difference. For DX, the
bent-half-wave should have been down on the quarter-wave (because some
of the radiation was being wasted at high angles); but in contests, both
antennas seemed to work the same regular DX stations. The bent half-wave
was louder for short-skip, which meant more QRM at night, but made it
easier to continue making low-point contacts during daylight hours.

If you use an 80m trap, the antenna could still work on 40m but the
horizontal section would be way over-long. Unless rapid band changing
between 80m and 160m is a priority, I'd suggest you use a physical
disconnect at the end of the 35ft horizontal section. (My setup made it
very easy to loosen a rope and lower the connection into reach, so I
used simple banana plugs, with snap links to add either wire or plain
cord.)




--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Length & number of radials
 

On Wed, 19 Jul 2006 13:03:16 -0500, "hasan schiers"
wrote:
Incidentally, over the weekend I tried to add a 40m wire parallel to the 80m
L...it was a complete failure. (I used a "fan" approach with 6" standoffs
for the 33' vertical wire). I thought I might get 2 fer 1 at the feedpoint,
but it just didn't work worth a darn.

Hi Hasan,

I must think that you were only slightly off in length, and that the
proximity, even at 6 inches, is still proximal.

Very low noise level, signals were
significantly weaker than my Carolina Windom 80 (on 40m) up 42'.

Not unlike many similar reports.

I did work
a few DX stations with it, but just not up to my expectations. A properly
performing 40m 1/4 w vertical over very good soil and a full radial field as
described in my prior message should have been outstanding. It wasn't.

Some of those same reporters suggest split operation where the
vertical is the radiator and a high horizontal is the receiving
antenna.

I wondered if I could EVALUATE the effectiveness of the 80m inverted L on
40m as a half wave, by temporarily taking an antenna tuner with wide range
(T-network matches almost anything) out to the feedpoint and matching it
there. If it hears well, and works ok at 300w (tuner limit), then it might
be worth investing in the coil/cap/relays to switch a more standard high-Z
feed in and out. What do you think?

I would encourage that, simply because you seem to be amenable to such
a path already. Gaining experience is always a noble work.

73's
Richard Clark, KB7QHC

Length & number of radials
 

What would NEC4 say?

Who or what is NEC4?

Length & number of radials
 

"Reg Edwards" wrote in message
...

What would NEC4 say?

Who or what is NEC4?

http://en.wikipedia.org/wiki/Numeric...magnetics_Code

Length & number of radials
 

You need at least an odd number of 1/4 wavelengths to satisfy the boundary
conditions.
You need at least three to define a plane (or cone, if you want a 50 ohm
feedpoint)

73
H.
NQ5H

Length & number of radials
 

"hasan schiers" wrote in message
...
I don't know about boundary conditions, but when I use this program
to
evaluate the following system:

3.62 Mhz, 18.3 meter height (simulating an inverted L with 25.4 ohms
Rrad)

Resistivity 25, Permittivity 25

2mm radials, 4mm antenna wire, radials 1 mm depth (actually #14
insulated
wire, stapled to the lawn and sinking in gradually)

..it shows my predicted efficiency with (26) 50' long radials to be
about
90%.

My measurements indicated I am getting about 88%. Pretty good
agreement.

=========================================
Yes Hasan, good agreement. How did you determine efficiency to THAT
degree of accuracy?
=========================================
What causes me to cringe, is that the program shows that I can
reduce the
length of my radials from 16.1 meters to a little over 4 meters
without
losing ANY significant efficiency. Given everything else I've read
over the
years, that just seems to be way too good to be true.
=========================================
You've been reading books and magazines about rules-of-thumb written
by old-wives. At 3.62 MHz and a radial length of 16 metres the
attenuation approaches 100 decibels. So there's no current flowing in
the radials beyond 5 metres. You can remove the excess 12 metres.
They are not doing anything. What small current density there is
beyond 5 metres is all flowing in the soil. The cross-sectional area
of the soil carries the small current just as well as the radials.
=========================================
Now, I suppose I could rip up my 26 radials and shorten them all to
about 5
meters and re-measure my efficiency, but that's a LOT of work (and
it's 97
degrees out with a dew point in the mid 70's). Not going to happen.

Here's the kicker... I have 1000' of remaining wire to put down (and
I am
going to add it). If this value of 4 or 5 meters (15 feet, let's
say) is
even remotely correct, I can put down 66 more radials (although they
would
be interlaced with the existing 26 longer ones of 50' each).

Using my initial length of 50', I can put down 20 more radials,
giving me a
total of 46 radials 50' long.
==========================================
Yes. Use the program to calculate efficiency with the extra 20
radials. Assume all the radials are 5 metres long. But you may not
think the meagre 3% or 0.13dB in efficiency is worth all the labour
and back-ache. By now you are beginning to appreciate how useful the
program is.
==========================================

Reg, you program seems to be telling me that I would get the maximum
benefit
by putting in 66 more radials approximately 15' long, and that
installing
them at 50' would be wasting 35' of wire per radial, and reducing
radial
coverage as well.

So...what should I do:

1. Add 66 greatly shortened radials (accepting Reg's program as
correct)

or

2. Add 20 radials, maintaining my 50' length that I originally used.

I look forward to comments.
==========================================

Hasan, if I were you I would lay some extra short radials between the
existing long radials - and get some Sloan's liniment to be massaged
into my back. But the increase in efficiency would be un-measurable.
You are fortunate to have very low soil resistivity. Mine is about 70
ohm-metres and for years on the 160m band I have had 7 radials about 3
metres long plus an incoming lead water pipe.
----
Reg, G4FGQ

Length & number of radials
 

Reg wrote among other stuff:

You've been reading books and magazines about rules-of-thumb written
by old-wives. At 3.62 MHz and a radial length of 16 metres the
attenuation approaches 100 decibels. So there's no current flowing in
the radials beyond 5 metres. You can remove the excess 12 metres.
They are not doing anything. What small current density there is
beyond 5 metres is all flowing in the soil. The cross-sectional area
of the soil carries the small current just as well as the radials.

==========================================
Yes. Use the program to calculate efficiency with the extra 20
radials. Assume all the radials are 5 metres long. But you may not
think the meagre 3% or 0.13dB in efficiency is worth all the labour
and back-ache. By now you are beginning to appreciate how useful the
program is.
==========================================

Reg,

NEC4 engine can accommodate on the ground or buried radials in modeling and
calculating vertical antenna parameters and performance.

I bet Roy has his hair standing up, or perhaps still trying to recover from
the "appreciation" of your program, unless he is still running calculations
:-)

You are trivilializing, ignoring 100 years or so of vertical antenna
research, measurements and misleading innocent users of your program. You
might be right in calculating the resonant frequency of piece of wire in the
dirt, but that is far from its contribution to the vertical antenna
performance and efficiency.
You better switch to some better quality vino and read up on the subject.
:-)


Yuri K3BU

Length & number of radials
 

NEC4 engine can accommodate on the ground or buried radials in
modeling and
calculating vertical antenna parameters and performance.

=======================================
How many weeks of user training does NEC4 require?

Hour many hours of work and imagination are required to enter input
data?

What is the purchase price of the latest version?

Is it legally available to non-USA citizens?
----
Reg, G4FGQ.

Length & number of radials
 

Reg Edwards wrote:
You've been reading books and magazines about rules-of-thumb written
by old-wives. At 3.62 MHz and a radial length of 16 metres the
attenuation approaches 100 decibels. So there's no current flowing in
the radials beyond 5 metres. You can remove the excess 12 metres.
They are not doing anything. What small current density there is
beyond 5 metres is all flowing in the soil. The cross-sectional area
of the soil carries the small current just as well as the radials.

How did you verify your program Reg?

I can go outside right now and measure current in a 40 meter vertical
radial system, and 100 feet from the base there is significant radial
current.

Your programs results also dramatically disagree with Brown, Lewis, and
Epstein's data in one of the most comprehensive radial studies ever
done.

73 tom

Length & number of radials
 

Your programs results also dramatically disagree with Brown, Lewis,
and
Epstein's data in one of the most comprehensive radial studies ever
done.

73 tom

=========================================

All three of B,L & E forgot to determine ground resistivity and
permittivity. That's hardly comprehensive!
----
Reg.