"Jerry" wrote in
:

....
The two 100 ohm loads in parallel give a 50 ohm load to the 50 ohm
coax
main feed line. I used a ferrite "balun" where the unbalanced 50
ohm *main feed line* connects to the center conductors that are
connected to be a 50 ohm load. .

You didn't mention the balun in your fist posting. Without an effective
balun, the system would be quite poor.

In each pair of antenna side coax lines where the shields are tied together
and the inners are used for a 100 ohm connection point, you drive one coax
in opposite phase to the other. Your description did not note that there is
particular phasing requirement for the coax lines to the antennas, and
polarity of connection of the DEs.

BTW, you have constructed a type of power divider. There are a lot of
different ways to do it.

Owen

"Owen Duffy" wrote in message
...
"Jerry" wrote in
:

...
The two 100 ohm loads in parallel give a 50 ohm load to the 50 ohm
coax
main feed line. I used a ferrite "balun" where the unbalanced 50
ohm *main feed line* connects to the center conductors that are
connected to be a 50 ohm load. .

You didn't mention the balun in your fist posting. Without an effective
balun, the system would be quite poor.

In each pair of antenna side coax lines where the shields are tied
together
and the inners are used for a 100 ohm connection point, you drive one coax
in opposite phase to the other. Your description did not note that there
is
particular phasing requirement for the coax lines to the antennas, and
polarity of connection of the DEs.

BTW, you have constructed a type of power divider. There are a lot of
different ways to do it.

Owen

the simpler way is to just parallel all 4 of the 50 ohm loads which gives
you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm coax
1/4 wave long to form a 25 ohm matching section, that will get you back to a
50 ohm common point with no need for a balun.

On Sun, 14 Dec 2008 21:54:45 GMT, "Dave" wrote:

BTW, you have constructed a type of power divider. There are a lot of
different ways to do it.

Owen

the simpler way is to just parallel all 4 of the 50 ohm loads which gives
you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm coax
1/4 wave long to form a 25 ohm matching section, that will get you back to a
50 ohm common point with no need for a balun.

Unfortunately, this would be a common mode nightmare.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 14 Dec 2008 21:54:45 GMT, "Dave" wrote:

BTW, you have constructed a type of power divider. There are a lot of
different ways to do it.

Owen

the simpler way is to just parallel all 4 of the 50 ohm loads which gives
you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm
coax
1/4 wave long to form a 25 ohm matching section, that will get you back to
a
50 ohm common point with no need for a balun.

Unfortunately, this would be a common mode nightmare.

73's
Richard Clark, KB7QHC


.... why? It's a way it's done for broadcasting antennas. There's little
reason why the screen of the feeder can run continuously into the screens of
the transformer sections and on into the screens of the cables that feed the
individual Yagis. If the drive-points of the Yagis are equipped with
adequate baluns then there should be no more common-mode current on the
outside of the continuous screen than for the case of a single Yagi.

Chris

"christofire" wrote in message
...

"Richard Clark" wrote in message
...
On Sun, 14 Dec 2008 21:54:45 GMT, "Dave" wrote:

BTW, you have constructed a type of power divider. There are a lot of
different ways to do it.

Owen

the simpler way is to just parallel all 4 of the 50 ohm loads which gives
you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm
coax
1/4 wave long to form a 25 ohm matching section, that will get you back
to a
50 ohm common point with no need for a balun.

Unfortunately, this would be a common mode nightmare.

73's
Richard Clark, KB7QHC


... why? It's a way it's done for broadcasting antennas. There's little
reason why the screen of the feeder can run continuously into the screens
of the transformer sections and on into the screens of the cables that
feed the individual Yagis. If the drive-points of the Yagis are equipped
with adequate baluns then there should be no more common-mode current on
the outside of the continuous screen than for the case of a single Yagi.

Chris

Of course I meant to type 'why the screen of the feeder can't run
continuously into ...'

On Sun, 14 Dec 2008 23:20:10 -0000, "christofire"
wrote:

50 ohm common point with no need for a balun.
If the drive-points of the Yagis are equipped with adequate baluns

And your question is about....?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 14 Dec 2008 23:20:10 -0000, "christofire"
wrote:

50 ohm common point with no need for a balun.
If the drive-points of the Yagis are equipped with adequate baluns

And your question is about....?

73's
Richard Clark, KB7QHC


Is this a quiz?

I simply questioned your statement that the very common arrangement of
star-point and transformer, implemented in co-axial line, should be 'a
common mode nightmare' as you put it. The middle portion of the diagram
(http://www.vk1od.net:80/lost/Fig6.png) posted at the beginning of this
thread shows baluns on the drive points of the dipoles and nowadays Yagi
antennas for amateur as well as professional use appear to be sold more
often with integral baluns. Co-axial feeders always interact to some extent
on account of their outer conductors being in the vicinity of the antenna(s)
but there are simple steps that can be taken to minimise this.

However, I concede there may be some reason to want to combine/power-split
using balanced line but ultimately it will need to be connected to a
co-axial line - if the intention is to achieve this without use of a balun
then I wonder if this would be more of a 'nightmare'.

Chris

On Mon, 15 Dec 2008 14:19:28 -0000, "christofire"
wrote:

Is this a quiz?
And then you allow:
However, I concede there may be some reason to want to combine/power-split
using balanced line but ultimately it will need to be connected to a
co-axial line - if the intention is to achieve this without use of a balun
then I wonder if this would be more of a 'nightmare'.

It must be a quiz - when I point out that Dave does not call out for
isolation (*ferrite* BalUns as have been identified through Jerry's
and Owen's correspondence) and as you do as an aside - then what is it
that you find debatable about my commonplace observation?

Common Mode doesn't disappear into the VHF/UHF. Common Mode creates a
complex impedance product that is generally unaccounted for (ignored),
and would certainly disturb phase relationships where phase
relationships are of primary importance.

The only other alternative is consuming transmission line in coils to
the same purpose. That hasn't been offered as a choice until now.

73's
Richard Clark, KB7QHC