On May 4, 6:51 am, james wrote:
Tomatch an antenna that is around 100 Ohms impedance needs only what
is called a quarter wave matching stub. It is simply an electrical
quarterwave length of 75 Ohm coax from the feedpoint to the 50Ohm
transmission line.
Simple and works well.

Problem is... the stub would be quite long... about nine feet.
I wouldn't want that much coax kicking around as a matching network.

www.telstar-electronics.com

On 4 May 2007 05:46:49 -0700, Telstar Electronics
wrote:

+++On May 4, 6:51 am, james wrote:
+++ Tomatch an antenna that is around 100 Ohms impedance needs only what
+++ is called a quarter wave matching stub. It is simply an electrical
+++ quarterwave length of 75 Ohm coax from the feedpoint to the 50Ohm
+++ transmission line.
+++ Simple and works well.
+++
+++Problem is... the stub would be quite long... about nine feet.
+++I wouldn't want that much coax kicking around as a matching network.
+++
+++www.telstar-electronics.com
**************

IF coax length is a hangup then you can use a two to one balun.
Actually the length will be between 66% and 80% of ~9 feet depending
on the dielectric constant of the material that comprises the coaxial
cable's center. Using RG11 polyethelene dielectric will yield about 6
feet.

Also considering that if you want vertical polarization the feedline
must come away from the feedpoint orthogonally the run of any length
of matching stub would be immaterial.

james

On May 4, 10:08 am, james wrote:
IF coax length is a hangup then you can use a two to one balun.

Much better idea...

www.telstar-electronics.com

On 4 May 2007 10:34:25 -0700, Telstar Electronics
wrote:

+++On May 4, 10:08 am, james wrote:
+++ IF coax length is a hangup then you can use a two to one balun.
+++
+++Much better idea...
+++
+++www.telstar-electronics.com
*********

Actually a quarter wave matching section is better in some ways. All
you really do is shorten the main transmission line by the length of
the matching section. No real big deal if you can use a ruler. Then
using a matching section does predicate the knowledge of using certain
tools like a calculator, ruler, a coax cutting and stripping tool and
finally a soldering iron.

james

On 4 May 2007 10:34:25 -0700, Telspam Electronics
wrote in
.com:

On May 4, 10:08 am, james wrote:
IF coax length is a hangup then you can use a two to one balun.

Much better idea...


Not really. Insertion loss of a [ferrite] balun could negate any gain
you may get by impedance matching. It is also fixed, while a coax stub
can be easily 'retuned' by simply pinning the coax. Not only that,
since the antenna is (hopefully) way up in the air, the coax used for
matching is either incorporated in the line or hung from the side,
making any worries about extra coax "kicking around" a non-issue. You
should be more worried about where you're going to put that nine
square feet of ground plane.

On May 4, 5:44 pm, Frank Gilliland wrote:
Not really. Insertion loss of a [ferrite] balun could negate any gain
you may get by impedance matching. It is also fixed, while a coax stub
can be easily 'retuned' by simply pinning the coax. Not only that,
since the antenna is (hopefully) way up in the air, the coax used for
matching is either incorporated in the line or hung from the side,
making any worries about extra coax "kicking around" a non-issue. You
should be more worried about where you're going to put that nine
square feet of ground plane.

Pure rubbish... a balun would have perhaps 0.1dB insertion loss. The
antenna gain is perhaps twenty times that!
www.telstar-electronics.com

IF coax length is a hangup then you can use a two to one balun.

This would be better.

Vinnie S.

On 4 May 2007 16:17:09 -0700, Telspam Electronics
wrote in
. com:

On May 4, 5:44 pm, Frank Gilliland wrote:
Not really. Insertion loss of a [ferrite] balun could negate any gain
you may get by impedance matching. It is also fixed, while a coax stub
can be easily 'retuned' by simply pinning the coax. Not only that,
since the antenna is (hopefully) way up in the air, the coax used for
matching is either incorporated in the line or hung from the side,
making any worries about extra coax "kicking around" a non-issue. You
should be more worried about where you're going to put that nine
square feet of ground plane.

Pure rubbish... a balun would have perhaps 0.1dB insertion loss. The
antenna gain is perhaps twenty times that!


"LOL!"

On 4 May 2007 16:17:09 -0700, Telstar Electronics
wrote:

+++On May 4, 5:44 pm, Frank Gilliland wrote:
+++ Not really. Insertion loss of a [ferrite] balun could negate any gain
+++ you may get by impedance matching. It is also fixed, while a coax stub
+++ can be easily 'retuned' by simply pinning the coax. Not only that,
+++ since the antenna is (hopefully) way up in the air, the coax used for
+++ matching is either incorporated in the line or hung from the side,
+++ making any worries about extra coax "kicking around" a non-issue. You
+++ should be more worried about where you're going to put that nine
+++ square feet of ground plane.
+++
+++Pure rubbish... a balun would have perhaps 0.1dB insertion loss. The
+++antenna gain is perhaps twenty times that!
+++www.telstar-electronics.com
+++
*************

Baluns and RF transformers can be loss. Many factors come into effect.
These include wire guage, operating frequency, power levels, load and
source vriations and core material. Also not to forget connetor
losses.

A well designed Balun or RF transformer will comparable low loss
performance of a coaxial matching section. There are some benefits for
RF transformers and baluns in that they are considerably more
broadbanded. Over narrow bandwidths the coaxial matching section can
be more tolerable to impedance variation from both the load and the
source.

james

On Fri, 04 May 2007 20:00:45 -0400, Vinnie S.
wrote:

+++
+++IF coax length is a hangup then you can use a two to one balun.
+++
+++This would be better.
+++
+++Vinnie S.
**********

2:1 RF transformers can be a tricky item to build. IF you use air core
you need sufficient inductance in both the primary and and secondary.
Our amatuer radio club did a 40 M and 80 M full wave loop for Field
Day about 20 yrs ago and used air core RF transformers. They were
rather large and the windings required support. They worked very well.
We were making contacts when otheres were complaining how poor the
bands were.

Good luck on which direction you choose.

ps. If you plan to add a reflector to the system then I would suggest
other methods of matching than a balun or RF transformer. With a
reflector, a gamma match would be suitable. So temper that with your
decision for future expansion.

james