Diameter of cable in coaxial Collinear antenna
 

Hi,

I am in the process of making a couple of 9dB Collinear antennas for 920
MHz.

I was wondering if the diameter of the coax is significant.

The design is simply 1/2 wavelength sections soldered centre to braid
with a 1/4 wave radiator at the top and a 1/4 wave sleeve choke and a
few ferrite toroid baluns at the bottom. The original design uses RG58
coax but I find this difficult to solder in short lengths and the
dielectric melts if the iron is left on too long. Instead I am using
RG174 PFTE dielectric. The Vp for both is still 0.66.

Thanks for any info

Regards

David

Diameter of cable in coaxial Collinear antenna
 

On Tue, 18 Oct 2005 09:00:12 +0000, David wrote:

Hi,

I am in the process of making a couple of 9dB Collinear antennas for 920
MHz.

I was wondering if the diameter of the coax is significant.

The design is simply 1/2 wavelength sections soldered centre to braid
with a 1/4 wave radiator at the top and a 1/4 wave sleeve choke and a
few ferrite toroid baluns at the bottom. The original design uses RG58
coax but I find this difficult to solder in short lengths and the
dielectric melts if the iron is left on too long. Instead I am using
RG174 PFTE dielectric. The Vp for both is still 0.66.

The Vp for PFTE is more like 0.695. I would suggest semi-rigid for this
application.

Bob, N7XY

Diameter of cable in coaxial Collinear antenna
 

Bob,

Thanks for your response. Why would you recommend semi-rigid ?

Bob Nielsen wrote:
On Tue, 18 Oct 2005 09:00:12 +0000, David wrote:


Hi,

I am in the process of making a couple of 9dB Collinear antennas for 920
MHz.

I was wondering if the diameter of the coax is significant.

The design is simply 1/2 wavelength sections soldered centre to braid
with a 1/4 wave radiator at the top and a 1/4 wave sleeve choke and a
few ferrite toroid baluns at the bottom. The original design uses RG58
coax but I find this difficult to solder in short lengths and the
dielectric melts if the iron is left on too long. Instead I am using
RG174 PFTE dielectric. The Vp for both is still 0.66.


The Vp for PFTE is more like 0.695. I would suggest semi-rigid for this
application.

Bob, N7XY

Diameter of cable in coaxial Collinear antenna
 

On Wed, 19 Oct 2005 00:08:42 +0000, David wrote:

Bob,

Thanks for your response. Why would you recommend semi-rigid ?

In my experience, you can more precisely control the length of the tubing
than with a braid shield. There is some mechanical rigidity advantage, as
well, although that isn't a big factor if you use some sort of dielectric
tube to contain the antenna.


Bob Nielsen wrote:
On Tue, 18 Oct 2005 09:00:12 +0000, David wrote:


Hi,

I am in the process of making a couple of 9dB Collinear antennas for 920
MHz.

I was wondering if the diameter of the coax is significant.

The design is simply 1/2 wavelength sections soldered centre to braid
with a 1/4 wave radiator at the top and a 1/4 wave sleeve choke and a
few ferrite toroid baluns at the bottom. The original design uses RG58
coax but I find this difficult to solder in short lengths and the
dielectric melts if the iron is left on too long. Instead I am using
RG174 PFTE dielectric. The Vp for both is still 0.66.


The Vp for PFTE is more like 0.695. I would suggest semi-rigid for this
application.

Bob, N7XY