monopole Design
 

Hello all,
in designing a monopole should i use the velocity factor of the wire in
the equation or not? and if i want its impedance to be 50ohm should i
use a matching network or is there another way?

On 11 Jun 2005 14:04:37 -0700, "redhat" wrote:

Hello all,
in designing a monopole should i use the velocity factor of the wire in
the equation or not? and if i want its impedance to be 50ohm should i
use a matching network or is there another way?

Are you sure you want 50-ohm impedance and not 37-ohms?

Danny, K6MHE

yes, i want to match it to a 50ohm amplifier,why do you think it should
be 37ohm, i have simulated it using EZNEC and the source impedance is
1.684 - J 4592, is there something wrong in that? it is 1/8 wavelength
monopole.
Regards

Well, undoubtedly...

the 1.684 is the "pure resistance value", and this would best be at 50
ohms...

if "- J 4592" is a real minus 4592 ohms cap reactance--it would be good
to insert a +Jx of 4592 ohms (an equal and opposite inductive
reactance)... so that Jx ends up zero...

.... at that time you will find the finals in the amp start lasting
indefinitely--and you will not be bothered replacing them every few
minutes or so...

Warmest regards,
John

"redhat" wrote in message
oups.com...
yes, i want to match it to a 50ohm amplifier,why do you think it
should
be 37ohm, i have simulated it using EZNEC and the source impedance is
1.684 - J 4592, is there something wrong in that? it is 1/8 wavelength
monopole.
Regards

redhat wrote:
yes, i want to match it to a 50ohm amplifier,why do you think it should
be 37ohm, i have simulated it using EZNEC and the source impedance is
1.684 - J 4592, is there something wrong in that? it is 1/8 wavelength
monopole.

Try a loading coil in the center of the 1/8 wavelength.
--
73, Cecil http://www.qsl.net/w5dxp


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what about the velocity factor of the wire, should i use it in the
equation of the antenna length or not?

On 11 Jun 2005 18:03:05 -0700, "redhat" wrote:

what about the velocity factor of the wire, should i use it in the
equation of the antenna length or not?

Hi OM,

Your problems with modeling go much further. The impedance you
reported was seriously low, even for an 1/8th wave. What others were
trying to communicate to you is that even the best 1/4th wave (a
standard sized whip or monopole) will only give you 35 to 37 Ohms, not
50 Ohms. However, this is rarely an issue in achieving good
performance. A 1 Ohm antenna, on the other hand, seriously begs close
examination, patience, and care in feeding.

73's
Richard Clark, KB7QHC

yes, a wire in free space has a velocity factor... if the formula for
the antenna in question does not all ready take that velocity factor
into consideration, you will need to consider the velocity...

.... there is also "end effect"...

.... simplest thing to do would be to use the formula which takes this
all into consideration...

.... first, I would google for "shortened antennas" or "shortened
radiators" and get a bit more familiar with "loading" the antenna to
resonance...

Warmest regards,
John
"redhat" wrote in message
ps.com...
what about the velocity factor of the wire, should i use it in the
equation of the antenna length or not?

On 11 Jun 2005 16:29:47 -0700, "redhat" wrote:

yes, i want to match it to a 50ohm amplifier,why do you think it should
be 37ohm, i have simulated it using EZNEC and the source impedance is
1.684 - J 4592, is there something wrong in that? it is 1/8 wavelength
monopole.
Regards

You hadn't stated that you were using a 1/8-wavelength monopole in
your original posting and I had assumed that you were discussing a
*standard* 1/4-wave monopole.

Danny, K6MHE

i have made a modification to it, it is now 1/4 wavelength monopole.
the simulation output is : source voltage= 3092 at -89.79 deg. and
impedance= 11.08-j3092 ohm . what is the meaning of this source
voltage? i have placed a source with amplitude 1v at 0% from E1 because
it is a monopole, the ground type is free space.

redhat wrote:
i have made a modification to it, it is now 1/4 wavelength monopole.
the simulation output is : source voltage= 3092 at -89.79 deg. and
impedance= 11.08-j3092 ohm . what is the meaning of this source
voltage? i have placed a source with amplitude 1v at 0% from E1 because
it is a monopole, the ground type is free space.

Sounds like the source is one amp, not one volt.
--
73, Cecil http://www.qsl.net/w5dxp


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On 12 Jun 2005 06:01:21 -0700, "redhat" wrote:

i have made a modification to it, it is now 1/4 wavelength monopole.
the simulation output is : source voltage= 3092 at -89.79 deg. and
impedance= 11.08-j3092 ohm . what is the meaning of this source
voltage? i have placed a source with amplitude 1v at 0% from E1 because
it is a monopole, the ground type is free space.

Something must be wrong with your model. A resonate 1/4-wave monopole
should have the resistance component around 20-ohms or so.
Additionally, it would appear by the high reactive component you give
that you do not have a ground plane included in you model. A 1/4-wave
monopole requires something to work against.

Danny, K6MHE

Do you have your ground planes separated from the radiator in the model?

Do you have the source placed at the bottom end of the radiator?

Perhaps one more versed in EZNEC would take a look if you would
post/offer the antenna file you have created here...

John

"redhat" wrote in message
ups.com...
i have made a modification to it, it is now 1/4 wavelength monopole.
the simulation output is : source voltage= 3092 at -89.79 deg. and
impedance= 11.08-j3092 ohm . what is the meaning of this source
voltage? i have placed a source with amplitude 1v at 0% from E1
because
it is a monopole, the ground type is free space.

the ground was set to "free space" and when i selected "perfect" ground
an error occured "one or more wires extended into or lying on the
ground", the problem was that in the wire coordinates z was set to 0
,when i selected a different z the problem was solved but the voltage
is still high, the antenna will be placed 90 deg. to the ground plane
so what should be z value? the source is placed 0% from E1
(monopole).note: i can't upload the file rightnow

redhat:

I don't want Roy jumping me about giving advice on his application...

However, you need to give the starting height of your elements some
distance above ground... actually, you would be wise to really make this
a "real" value, like the actual height the antenna will be...

.... for example, say you have an eight foot long vertical radiator at
ten feet above ground--then one x,y value will be 10.0 and the ending
x,y value will be 18.0...

I hope that is clear enough, Roy Lewellan would best be consulted on
EZNEC's exact workings...

John

"redhat" wrote in message
oups.com...
the ground was set to "free space" and when i selected "perfect"
ground
an error occured "one or more wires extended into or lying on the
ground", the problem was that in the wire coordinates z was set to 0
,when i selected a different z the problem was solved but the voltage
is still high, the antenna will be placed 90 deg. to the ground plane
so what should be z value? the source is placed 0% from E1
(monopole).note: i can't upload the file rightnow

the ground was set to "free space" and when i selected "perfect" ground

an error occured "one or more wires extended into or lying on the
ground", the problem was that in the wire coordinates z was set to 0
,when i selected a different z the problem was solved but the voltage
is still high, the antenna will be placed 90 deg. to the ground plane
so what should be z value?should it be the same length of the antenna?
the source is placed 0% from E1 (monopole). the pattern of the antenna
shows a gain of 1.5dbi ,if i have a circuit that outputs 2db for
example then the output from the antenna should be 3.5db, right? or
because dbi is referenced to isotropic source there is a conversion?
note: i can't upload the file rightnow

On 12 Jun 2005 15:58:04 -0700, "redhat" wrote:
an error occured

Hi OM,

As I pointed out some time ago, your work is very far off track.

It would be far simpler to start with a working design and change it
slightly to observe how your input effects the results.

Simply hit the Open button and select:
VERT1.EZ
and look at ALL the characteristics. This may mean starting a
notebook (standard Engineering discipline) and logging those values.
Make a change (like shorten or lengthen the ONLY wire) and look at ALL
the characteristics. Log those values and compare to the first.

Keep doing this and eventualy you will find that
the velocity factor of the wire
is not very significant - or better yet, discover what significance it
has (it will eventually become significant, but not practically so)
and report your results here.

73's
Richard Clark, KB7QHC

Richard:

That was uncommonly decent of you, it is good to see one man giving
another a "hand up."

Also, it is excellent advice I failed to even think of telling him...

Warmest regards,
John

"Richard Clark" wrote in message
...
On 12 Jun 2005 15:58:04 -0700, "redhat" wrote:
an error occured

Hi OM,

As I pointed out some time ago, your work is very far off track.

It would be far simpler to start with a working design and change it
slightly to observe how your input effects the results.

Simply hit the Open button and select:
VERT1.EZ
and look at ALL the characteristics. This may mean starting a
notebook (standard Engineering discipline) and logging those values.
Make a change (like shorten or lengthen the ONLY wire) and look at ALL
the characteristics. Log those values and compare to the first.

Keep doing this and eventualy you will find that
the velocity factor of the wire
is not very significant - or better yet, discover what significance it
has (it will eventually become significant, but not practically so)
and report your results here.

73's
Richard Clark, KB7QHC

in designing a monopole should i use the velocity factor of the wire
in
the equation or not?

No...It's silly...Do you check the VF of wire when you
build a dipole? It's overkill worrying....The VF of straight
wire is in the 95+ range...Not enough to worry about...

and if i want its impedance to be 50ohm should i
use a matching network or is there another way?

There is no other way. If you want to build a 1/8 wave
vertical, build it the same way you would build a mobile
vertical. If not top loaded with a hat, you should use a
loading coil at 1/2 to 3/4 up the vertical for best efficiency.
You would use a matching device of the same type used
for most mobiles. If you want to tinker with vertical design,
I'd try something like Reg's "vertload" to design the antenna.
It will tell the appx efficiency of the design, and also give you the
values needed for a matching device, which can be a simple
coil or cap depending how you set it up. Then, after that is
done, you can try modeling it. Short vertical design is quite
mature...You are not going to be able to reinvent the wheel...
MK

On 12 Jun 2005 15:37:32 -0700, "redhat" wrote:

the ground was set to "free space" and when i selected "perfect" ground
an error occured "one or more wires extended into or lying on the
ground", the problem was that in the wire coordinates z was set to 0
,when i selected a different z the problem was solved but the voltage
is still high, the antenna will be placed 90 deg. to the ground plane
so what should be z value? the source is placed 0% from E1
(monopole).note: i can't upload the file rightnow

Why don't you move the source to the bottom (ground) end of the
monopole? I'm guessing that E1 is the top of the vertical.

Use "View Antenna" to see for sure. You can use Z=0 if you use
MiniNEC ground.