Vertical antenna problem
 

Hello,
I build lambda/4 vertical for 20m (i used the fishing pole).
The vertical and radials are build from insulated wire 2.5 square
millimeters.
I have used formula on internet and Eznec so I cut 5,09meters wire for
vertical and 4 pieces 5.25m wire for radials (i left radials longer so I can
cut them to make fine tuning of antenna).
I wanted minimal SWR on 14.050MHz.
But now I have minimal SWR on 12.800 MHz . :-)
According to Eznec if I short the radials for 2meters (so they will be long
3.25m) that will rise resonant frequency around 1.2MHz.
But it is not logic to me. So short radials?
Also according to Eznec if I short vertical to 4.7meters and radials to
4.7meters that will also rise resonant frequency arround 1.2MHz.
Could that be that my mistake is that I didn't calculate the velocity factor
for wire.
Maybe i should calculate it because I used single wire instead of aluminum
tube.
Or maybe some surrounding objects are influencing. I have metal mast for
loop antenna 5meters from vertical.
It is easier to cut radials (because I don't have to take down the whole
antenna).
What do You suggest?
To cut only radials to 3.25m or vertical and radials to 4.7m?
What is better?
Just to mentioned that I tuned antenna with tuner and it works great for
DXing.
73 9A4MN Neno

Vertical antenna problem
 

Well it seem that Google has the answer.
I found that lot of people are talking about influence of wire insulation on
velocity factor.
I didn't know that this influence is so big.
I think that the best solution is to cut radial and vertical to length 4.7m.
73 9A4MN Neno


"neno" wrote in message
...
Hello,
I build lambda/4 vertical for 20m (i used the fishing pole).
The vertical and radials are build from insulated wire 2.5 square
millimeters.
I have used formula on internet and Eznec so I cut 5,09meters wire for
vertical and 4 pieces 5.25m wire for radials (i left radials longer so I
can cut them to make fine tuning of antenna).
I wanted minimal SWR on 14.050MHz.
But now I have minimal SWR on 12.800 MHz . :-)
According to Eznec if I short the radials for 2meters (so they will be
long 3.25m) that will rise resonant frequency around 1.2MHz.
But it is not logic to me. So short radials?
Also according to Eznec if I short vertical to 4.7meters and radials to
4.7meters that will also rise resonant frequency arround 1.2MHz.
Could that be that my mistake is that I didn't calculate the velocity
factor for wire.
Maybe i should calculate it because I used single wire instead of aluminum
tube.
Or maybe some surrounding objects are influencing. I have metal mast for
loop antenna 5meters from vertical.
It is easier to cut radials (because I don't have to take down the whole
antenna).
What do You suggest?
To cut only radials to 3.25m or vertical and radials to 4.7m?
What is better?
Just to mentioned that I tuned antenna with tuner and it works great for
DXing.
73 9A4MN Neno

Vertical antenna problem
 

On 31 ago, 08:56, "neno" wrote:
Hello,
I build lambda/4 vertical for 20m (i used the fishing pole).
The vertical and radials are build from insulated wire 2.5 square
millimeters.
I have used formula on internet and Eznec so I cut 5,09meters wire for
vertical and 4 pieces 5.25m wire for radials (i left radials longer so I can
cut them to make fine tuning of antenna).
I wanted minimal SWR on 14.050MHz.
But now I have minimal SWR on 12.800 MHz . :-)
According to Eznec if I short the radials for 2meters (so they will be long
3.25m) that will rise resonant frequency around 1.2MHz.
But it is not logic to me. So short radials?
Also according to Eznec if I short vertical to 4.7meters and radials to
4.7meters that will also rise resonant frequency arround 1.2MHz.
Could that be that my mistake is that I didn't calculate the velocity factor
for wire.
Maybe i should calculate it because I used single wire instead of aluminum
tube.
Or maybe some surrounding objects are influencing. I have metal mast for
loop antenna 5meters from vertical.
It is easier to cut radials (because I don't have to take down the whole
antenna).
What do You suggest?
To cut only radials to 3.25m or vertical and radials to 4.7m?
What is better?
Just to mentioned that I tuned antenna with tuner and it works great for
DXing.
73 9A4MN Neno

Hello Neno,

Influence of PVC wire insulation on wave propagation is just a few
percent. Most of the field lines go through air. I did a calculation
myself (however results are in Dutch language). When the wire is
thicker, the influence of same layer of insulation becomes less.

The soil has significant influence on resonant frequency and steepness
of resonance of the radials. When you use many of them the length
becomes less critical. You can also use elevated radials (for example
about 4 radials 1..2 m above ground).

However when VSWR is OK with short radiator or shorter radials and you
don't have common mode problems in the coaxial feed line, I would not
worry.

When you are still curious, you might model the nearby structures in
your NEC file and try to simulate the influence. A mast at 5m distance
is within the near field, so you may expect some coupling.

Instead of cutting, you can also roll them up (beginning at the end),
so you can re-extend them when required).

Best regards,

Wim
PA3DJS
www.tetech.nl

Vertical antenna problem
 

"neno" wrote in message
...
Hello,
I build lambda/4 vertical for 20m (i used the fishing pole).
The vertical and radials are build from insulated wire 2.5 square
millimeters.
I have used formula on internet and Eznec so I cut 5,09meters wire for
vertical and 4 pieces 5.25m wire for radials (i left radials longer so I
can cut them to make fine tuning of antenna).
I wanted minimal SWR on 14.050MHz.
But now I have minimal SWR on 12.800 MHz . :-)
According to Eznec if I short the radials for 2meters (so they will be
long 3.25m) that will rise resonant frequency around 1.2MHz.
But it is not logic to me. So short radials?
Also according to Eznec if I short vertical to 4.7meters and radials to
4.7meters that will also rise resonant frequency arround 1.2MHz.
Could that be that my mistake is that I didn't calculate the velocity
factor for wire.
Maybe i should calculate it because I used single wire instead of aluminum
tube.
Or maybe some surrounding objects are influencing. I have metal mast for
loop antenna 5meters from vertical.
It is easier to cut radials (because I don't have to take down the whole
antenna).
What do You suggest?
To cut only radials to 3.25m or vertical and radials to 4.7m?
What is better?
Just to mentioned that I tuned antenna with tuner and it works great for
DXing.
73 9A4MN Neno

What is the SWR at 14.05? Assuming a good ground, at resonance the SWR will
be 1.5:1for 50 Ohm coax; 2:1 for 75 Ohm.

Tam/WB2TT

Vertical antenna problem
 

neno wrote:
What do You suggest?
To cut only radials to 3.25m or vertical and radials to 4.7m?
What is better?

Or (3) you could leave the radials as they are
and shorten the vertical wire.

The physical environment will shift the
resonant frequency away from that predicted
by EZNEC as modeling is not an exact science.

Any of the three choices will work and none of
them will result in the exact resonant frequency
you desire. In the end, to get the frequency
exact, you will be required to "cut and try" in
an iterative process that often forces you to
add back one inch of the two inches you just
removed. :-)
--
73, Cecil http://www.w5dxp.com

Vertical antenna problem
 

What is the SWR at 14.05? Assuming a good ground, at resonance the SWR
will be 1.5:1for 50 Ohm coax; 2:1 for 75 Ohm.

Tam/WB2TT


I have 1.3:1 for 50 Ohm coax now.
Look my answer to Cecil.
73

Vertical antenna problem
 

"Cecil Moore" wrote in message
. ..
neno wrote:
What do You suggest?
To cut only radials to 3.25m or vertical and radials to 4.7m?
What is better?

Or (3) you could leave the radials as they are
and shorten the vertical wire.

The physical environment will shift the
resonant frequency away from that predicted
by EZNEC as modeling is not an exact science.

Any of the three choices will work and none of
them will result in the exact resonant frequency
you desire. In the end, to get the frequency
exact, you will be required to "cut and try" in
an iterative process that often forces you to
add back one inch of the two inches you just
removed. :-)
--
73, Cecil http://www.w5dxp.com

I decided to cut radials because it was the easiest job considering that
vertical is elevated 9m up the ground.
I cut radials to 3.25m and now the SWR is 1.3:1 on 14.020 .
I left the vertical to 5.1m .
I will test the antenna this days.
Thanks for help.
Eznec was very helpful also.
73 9A4MN Neno

Vertical antenna problem
 

Hello Neno,

Influence of PVC wire insulation on wave propagation is just a few
percent. Most of the field lines go through air. I did a calculation
myself (however results are in Dutch language). When the wire is
thicker, the influence of same layer of insulation becomes less.

The soil has significant influence on resonant frequency and steepness
of resonance of the radials. When you use many of them the length
becomes less critical. You can also use elevated radials (for example
about 4 radials 1..2 m above ground).

However when VSWR is OK with short radiator or shorter radials and you
don't have common mode problems in the coaxial feed line, I would not
worry.

When you are still curious, you might model the nearby structures in
your NEC file and try to simulate the influence. A mast at 5m distance
is within the near field, so you may expect some coupling.

Instead of cutting, you can also roll them up (beginning at the end),
so you can re-extend them when required).

Best regards,

Wim
PA3DJS
www.tetech.nl


Thanks for help.
I cut radials to 3.25m and left vertical to 5.1m .
Now SWR is 1.3:1 on 14.020
I hope it will work good.
Eznec was very helpful too.
73 9A4MN Neno