OK, let's discuss dipoles vs length
 

Ralph Mowery wrote:

wrote in message
...
I've done a lot of modeling with V's and inverted V's. Except for a slight
diffenence due to ground effects at low heights, there is no difference
between them.

As the angle goes from 180 degrees, i.e. a dipole, the impedance goes
down and and the pattern spreads out.


I have not played with the programs , but often wondered what the effect is
on antennas that are suported on the ends and the middle is dropped in a U
or V shape and not the inverted V shape. Many antenna books and articals
seem to show the flat top and inverted V paterns, but I have not seen any
with the actual V type.

Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.


--
Jim Pennino

OK, let's discuss dipoles vs length
 

OK, let's discuss dipoles vs length
 

In message ,
writes
Look at this for an overview of NEC.

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

At the bottom under External links you will find both free and commercial
implementations.

EZNEC by W7EL is popular among hams and has a free demo version that is
fully functional but limited in how complex a model you can generate.

NEC itself just crunches and produces numbers, but there are several
versions, including EZNEC, which have graphical interfaces to make
it easier to build the model and view the results.

I've used EZNEC+ for years.


I use 4NEC2 - it's free ! Arie Voors used to post here, but I've not
seen anything from him for some time. MMANA is good too, but there's a
lot it can't do.

73 Brian GM4DIJ
--
Brian Howie

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

OK, let's discuss dipoles vs length
 

OK, let's discuss dipoles vs length
 

John S wrote:
On 10/12/2014 1:21 PM, wrote:
John S wrote:
On 10/11/2014 12:51 PM, wrote:
John S wrote:

snip

OK, so lets analyze my results:

Conditions are free space, wire is #14 gauge but may have zero ohms
where noted. The antenna is a dipole with the source connected at the
center, F=7MHz. I'm using EZNEC with a source of 1 watt. Antenna
resonance plays no part in this. # segments = 99 unless otherwise noted.

Lambda Wire Rin Gavg(dbi) Gmax(dbi) Efficiency

0.5 zero 80 0 2.16 100%
0.5 #14 73.6 -.09 2.08 98%

0.25 zero 13.2 0 1.85 100%
0.25 #14 13.7 -.17 1.69 96%

0.125 zero 3 0 1.78 100%
0.125 #14 3.25 -.33 1.45 93%

0.05 zero .464 0 1.76 100%
0.05 #14 .556 -.78 0.98 83%

Rin is the terminal resistance only. Gave is the average gain integrated
over the pattern, Gmax is the highest gain detected.

Unless I have done something wrong, I see that a dipole that is .05
wavelengths long is within 20% of being as efficient as a half-wave
dipole. Even including wire resistance.

I invite discussion in any case.

The diameter of #14 solid wire is 0.0641"; how about a line for #8, which
is 0.1285"?


0.05 #8 0.515 -.41 1.36 91.1%


Free space, no ground loss.

So it seems that a .05 lamda dipole is only about 7% less efficient than
a full size dipole wit suitable wire...

So much for "short antennas are not efficient".

(snip extraneous input)


Yes, Jim, that is so. In fact, that was the hidden reason for the
exercise. I was hoping this would provide an example to let others know
that it is not the antenna length that is the problem as Gareth
proposed. I was hoping that others would take the investigation into
their own hands as a result.

I noted that you tried to foul me up with the unreasonable wire size.
EZNEC has a nice warning feature to take care of it.

What "unreasonable wire size"? #8 wire is readily available and often
used to make antenna elements, as is 1/8 th aluminum, which is only a
few thousands of an inch different.

Or are you refering to issues with segmentation and fat, short wires which I
thought I had warned you about?


--
Jim Pennino

OK, let's discuss dipoles vs length
 

Lostgallifreyan wrote:
Lostgallifreyan wrote in
:

Seconded. I'll admit at this point welcoming an easy start, and a
prepared example of this would be a hell of an incentive for me to get
into exploring NEC too.


Actually to be fair, with ,y longwire tests I'll likely be using very thin
strong stainless wire and pulling it tight enough to reduce my need to worry
about it much. STill interesting though, I've seen heavy-looking HF antennas
strung over the apex of a roof in a valley near here, and that had a
pronounced sag that may or may not have been bothersome to whoever owned it.

You might want to read this before you put up stainless steel wi

http://www.mwrs.org.au/2011/06/23/an...eel-vs-copper/

There is a link to a report in there.



--
Jim Pennino

OK, let's discuss dipoles vs length
 

Lostgallifreyan wrote:
wrote in :

I doubt you will see any significant difference.

I've done a lot of modeling with V's and inverted V's. Except for a slight
diffenence due to ground effects at low heights, there is no difference
between them.


Fair enough. I've seen antennas loaded down with feedline but given that V
forms are used well, the slight V in those cases, let alone some sag, might
not be a concern for me. My main interest came out of my wish to try a
befavare antenna I can install almost as fast as I can run the distance. That
one would have no support over at least a half mile, and I don't yet know
whether it will be mechanically sound till I finish designing and making it.

A half mile is a long distance.

I hope you have the equations for the sag and tension on the wire at hand
and run through them first.

As I recall, both charts and calculators can be found on the 'net.


--
Jim Pennino

OK, let's discuss dipoles vs length
 

In message ,
writes
Ralph Mowery wrote:

wrote in message
...
I've done a lot of modeling with V's and inverted V's. Except for a slight
diffenence due to ground effects at low heights, there is no difference
between them.

As the angle goes from 180 degrees, i.e. a dipole, the impedance goes
down and and the pattern spreads out.


I have not played with the programs , but often wondered what the effect is
on antennas that are suported on the ends and the middle is dropped in a U
or V shape and not the inverted V shape. Many antenna books and articals
seem to show the flat top and inverted V paterns, but I have not seen any
with the actual V type.

Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.

Assuming it's a halfwave dipole, I would have thought it was better to
concentrate on getting the centre (where the current is) as high as
possible, rather than the ends. [Obviously this depends on whether you
have a suitable sky-hook available for and at the centre.] However, I
believe that there is at least one commercial loaded dipole (essentially
for portable use, I think) that has a short mast, and the ends of the V
are up in the air.

Also, regarding the radiation pattern, as the ends are dropped, doesn't
the signal that starts coming off the ends have an increasingly
vertically-polarised component?


--
Ian

OK, let's discuss dipoles vs length
 

wrote in :

You might want to read this before you put up stainless steel wi

http://www.mwrs.org.au/2011/06/23/an...eel-vs-copper/

There is a link to a report in there.


I will, but I have also seen several claims that at least for listenign
purposes, stainless isn't so bad, and that except when driving an antenna
with power, it may not matter what metal is used. No worries though, it's
cheap, I've got it, and I'll try it. :) If it fails, I'll get some hard-drawn
copper.

OK, let's discuss dipoles vs length
 

Lostgallifreyan wrote:
wrote in :

You might want to read this before you put up stainless steel wi

http://www.mwrs.org.au/2011/06/23/an...eel-vs-copper/

There is a link to a report in there.


I will, but I have also seen several claims that at least for listenign
purposes, stainless isn't so bad, and that except when driving an antenna
with power, it may not matter what metal is used. No worries though, it's
cheap, I've got it, and I'll try it. :) If it fails, I'll get some hard-drawn
copper.

Claims are like belly buttons; everyone has one.

These guys did an actual study.

If nothing else, the stainless could be used as a support for the copper.


--
Jim Pennino