Prev: NEWS: Hotspot sniffer eavesdrops on iPhone [VoIP & video] inreal-time
Next: Time machine & SuperDuper!
From: amdx on 14 Nov 2009 13:05
Hi All,
I'm having a disagreement about the use of this folded dipole calculator
impedance calculator.
http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html
We are using it to calculate the impedance of folded dipoles to drive a
yagi.
When entering data it asks for "Simple dipole feed impedance (ohms)"
Default is 72 ohms. This assumes a 1/2 wave dipole.
The fellow I'm disagreeing with say's,
"the reason that the variable in the calculator for the "dipole feed
impedance"
could be if you want to transform the z to something else, such as 50 ohms."
I don't even understand what he means.
I can only think of one reason to alter the 72 ohms, that would be if you
use a a different length folded dipole.
I'll readily admit the other fellow knows more about this than me, but
I need more convincing :-)
Can anyone explain this to me.
Thanks, Mike



From: Tony Hwang on 14 Nov 2009 13:23
amdx wrote:
> Hi All,
> I'm having a disagreement about the use of this folded dipole calculator
> impedance calculator.
> http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html
> We are using it to calculate the impedance of folded dipoles to drive a
> yagi.
> When entering data it asks for "Simple dipole feed impedance (ohms)"
> Default is 72 ohms. This assumes a 1/2 wave dipole.
> The fellow I'm disagreeing with say's,
> "the reason that the variable in the calculator for the "dipole feed
> impedance"
> could be if you want to transform the z to something else, such as 50 ohms."
> I don't even understand what he means.
> I can only think of one reason to alter the 72 ohms, that would be if you
> use a a different length folded dipole.
> I'll readily admit the other fellow knows more about this than me, but
> I need more convincing :-)
> Can anyone explain this to me.
> Thanks, Mike
>
>
>
Hi,
The eq. seems right. Folded dipole is basically a loop.
Usually we use 300 Ohm feeder.
Tony
VE6CGX
From: Tony Hwang on 14 Nov 2009 13:28
Tony Hwang wrote:
> amdx wrote:
>> Hi All,
>> I'm having a disagreement about the use of this folded dipole calculator
>> impedance calculator.
>> http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html
>> We are using it to calculate the impedance of folded dipoles to drive a
>> yagi.
>> When entering data it asks for "Simple dipole feed impedance (ohms)"
>> Default is 72 ohms. This assumes a 1/2 wave dipole.
>> The fellow I'm disagreeing with say's,
>> "the reason that the variable in the calculator for the "dipole feed
>> impedance"
>> could be if you want to transform the z to something else, such as 50
>> ohms."
>> I don't even understand what he means.
>> I can only think of one reason to alter the 72 ohms, that would be if you
>> use a a different length folded dipole.
>> I'll readily admit the other fellow knows more about this than me, but
>> I need more convincing :-)
>> Can anyone explain this to me.
>> Thanks, Mike
>>
>>
>>
> Hi,
> The eq. seems right. Folded dipole is basically a loop.
> Usually we use 300 Ohm feeder.
> Tony
> VE6CGX
Hi,
And you can use a tranformer 300 Ohm to 75 Ohm to use coax if need.
It becomes a from 300 Ohm balaanced to 75 Ohm unbalanced feed.
From: Tim Wescott on 14 Nov 2009 13:36
On Sat, 14 Nov 2009 12:05:21 -0600, amdx wrote:

> Hi All,
> I'm having a disagreement about the use of this folded dipole
> calculator
> impedance calculator.
> http://www.k7mem.150m.com/Electronic_Notebook/antennas/
folded_dipole.html
> We are using it to calculate the impedance of folded dipoles to drive a
> yagi.
> When entering data it asks for "Simple dipole feed impedance (ohms)"
> Default is 72 ohms. This assumes a 1/2 wave dipole.
> The fellow I'm disagreeing with say's,
> "the reason that the variable in the calculator for the "dipole feed
> impedance"
> could be if you want to transform the z to something else, such as 50
> ohms."
> I don't even understand what he means.
> I can only think of one reason to alter the 72 ohms, that would be if
> you use a a different length folded dipole.
> I'll readily admit the other fellow knows more about this than me, but
> I need more convincing :-)
> Can anyone explain this to me.
> Thanks, Mike

The way I read it is that you put in the feed impedance that a similar-
length plain-ol' dipole in the same situation would have. In a Yagi this
can be significantly lower than 72 ohms, which is the whole reason you're
considering a folded dipole.

Does the author have contact information? Perhaps you could ask the
source?

--
www.wescottdesign.com
From: amdx on 14 Nov 2009 13:49

"Tony Hwang" <dragon40(a)shaw.ca> wrote in message
news:hACLm.21858$de6.6577(a)newsfe21.iad...
> amdx wrote:
>> Hi All,
>> I'm having a disagreement about the use of this folded dipole
>> calculator
>> impedance calculator.
>> http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html
>> We are using it to calculate the impedance of folded dipoles to drive a
>> yagi.
>> When entering data it asks for "Simple dipole feed impedance (ohms)"
>> Default is 72 ohms. This assumes a 1/2 wave dipole.
>> The fellow I'm disagreeing with say's,
>> "the reason that the variable in the calculator for the "dipole feed
>> impedance"
>> could be if you want to transform the z to something else, such as 50
>> ohms."
>> I don't even understand what he means.
>> I can only think of one reason to alter the 72 ohms, that would be if you
>> use a a different length folded dipole.
>> I'll readily admit the other fellow knows more about this than me, but
>> I need more convincing :-)
>> Can anyone explain this to me.
>> Thanks, Mike
>>
>>
>>
> Hi,
> The eq. seems right. Folded dipole is basically a loop.
> Usually we use 300 Ohm feeder.
> Tony
> VE6CGX

In what case would I alter the 72 ohms?
Mike


 |  Next  |  Last
Pages: 1 2 3
Prev: NEWS: Hotspot sniffer eavesdrops on iPhone [VoIP & video] inreal-time
Next: Time machine & SuperDuper!