In the latest QST there is an article on a Window line twin lead antenna
that uses relays to switch sections in and out of a dipole configuration
to allow multiband use. (DC is inserted into the coax to activate the
relays.)

Sounds interesting to me.

But...the twin lead is connected directly to coax with no balun. Isn't
this a mismatch? I wonder about significant RF coupling to the adjacent
dipole sections through the relay assemblies. Also, I couldn't tell if
the window line was shorted into a loop at the ends or not.

Any comments?

Thanks

John
AB8O

jawod wrote:
In the latest QST there is an article on a Window line twin lead antenna
that uses relays to switch sections in and out of a dipole configuration
to allow multiband use. (DC is inserted into the coax to activate the
relays.)

Sounds interesting to me.

But...the twin lead is connected directly to coax with no balun. Isn't
this a mismatch? I wonder about significant RF coupling to the adjacent
dipole sections through the relay assemblies. Also, I couldn't tell if
the window line was shorted into a loop at the ends or not.

Any comments?

Thanks

John
AB8O
The impedance of the dipole is in the 200 to 600 ohm range. The
transmission line is a fair match for the antenna element. A transmatch
is required at the transmitter end though.

Dave WD9BDZ

"David G. Nagel" wrote in message
...
jawod wrote:
In the latest QST there is an article on a Window line twin lead antenna
that uses relays to switch sections in and out of a dipole configuration
to allow multiband use. (DC is inserted into the coax to activate the
relays.)

Sounds interesting to me.

But...the twin lead is connected directly to coax with no balun. Isn't
this a mismatch? I wonder about significant RF coupling to the adjacent
dipole sections through the relay assemblies. Also, I couldn't tell if
the window line was shorted into a loop at the ends or not.

Any comments?

Thanks

John
AB8O
The impedance of the dipole is in the 200 to 600 ohm range. The
transmission line is a fair match for the antenna element. A transmatch is
required at the transmitter end though.

Dave WD9BDZ

It's not a folded dipole. Both wires are fed in phase, and the second wire
is needed for a DC return only.

Tam/WB2TT

jawod wrote:
But...the twin lead is connected directly to coax with no balun. Isn't
this a mismatch?

The ladder-line is NOT used as RF transmission line.
It is used for DC current and for RF antenna current.
This is just an ordinary coax-fed dipole with an extra
wire to carry the DC. There is no BALanced to UNbalanced
RF junction to worry about.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
...
jawod wrote:
But...the twin lead is connected directly to coax with no balun. Isn't
this a mismatch?

The ladder-line is NOT used as RF transmission line.
It is used for DC current and for RF antenna current.
This is just an ordinary coax-fed dipole with an extra
wire to carry the DC. There is no BALanced to UNbalanced
RF junction to worry about.
--
73, Cecil http://www.w5dxp.com
-
QST antenna designs would be easier to understand if QST used the
traditional electrical diagrams for antennas, instead of those goofball
drawings that have insulators/guy wires/etc. shown as major features. This
particular antenna design, unlike some of the other antenna articles, can be
waded through by looking at the drawing.

Cecil Moore wrote:
There is no BALanced to UNbalanced RF junction to worry about.

Make that "transmission line junction". Of course, the
UNbalanced coax to BALanced dipole connection could use
a 1:1 choke.
--
73, Cecil http://www.w5dxp.com

jawod wrote:
In the latest QST there is an article on a Window line twin lead antenna
that uses relays to switch sections in and out of a dipole configuration
to allow multiband use. (DC is inserted into the coax to activate the
relays.)

Sounds interesting to me.

But...the twin lead is connected directly to coax with no balun. Isn't
this a mismatch? I wonder about significant RF coupling to the adjacent
dipole sections through the relay assemblies. Also, I couldn't tell if
the window line was shorted into a loop at the ends or not.

It is not a folded dipole.

The two sides of the ladder line are connected together at RF at the
input by capacitors C4 and C5 in the splitter making it look like a
slightly fat, ordinary dipole.

If you want to know about RF coupling on the adjacent elements, you
could model it with the demo version of EZNEC.

--
Jim Pennino

Remove .spam.sux to reply.

jawod wrote:
In the latest QST there is an article on a Window line twin lead antenna
that uses relays to switch sections in and out of a dipole configuration
to allow multiband use. (DC is inserted into the coax to activate the
relays.)

Sounds interesting to me.

But...the twin lead is connected directly to coax with no balun. Isn't
this a mismatch? I wonder about significant RF coupling to the adjacent
dipole sections through the relay assemblies. Also, I couldn't tell if
the window line was shorted into a loop at the ends or not.

Any comments?

Thanks

John
AB8O
Thanks to all for the enlightenment. I appreciate it.

73

John
AB8O