Hi,

I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz.
After pulling the unit apart and studying the construction, I am not
sure what style of antenna this is.

The antenna consists of an SMA plug that has RF178 cable soldered to
centre pin and
it appears earth braid is connected to ground side of plug.

The cable goes up the inside of 1 6mm Nylon tube for 40mm and then
exits the tube and winds around 4.5T. It then enters the tube
again and runs another 80mm. At this point the earth braid is stripped
leaving only the centre conductor and dielectric to continue another 70mm
to the top of the Radome (Nylon tube).

I understand the construction of 5/8 antenna but I would not expect the
braid to be earthed.

Thanks in advance for any help.

Regards

David

the 4.5 turns is a choke that cuts off the bottom part of the braid from the
top. the top 80mm and 70mm parts are then just a vertical dipole with the
feedpoint at the spot where the braid stops.

"David" wrote in message
...
Hi,

I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz.
After pulling the unit apart and studying the construction, I am not sure
what style of antenna this is.

The antenna consists of an SMA plug that has RF178 cable soldered to
centre pin and
it appears earth braid is connected to ground side of plug.

The cable goes up the inside of 1 6mm Nylon tube for 40mm and then
exits the tube and winds around 4.5T. It then enters the tube
again and runs another 80mm. At this point the earth braid is stripped
leaving only the centre conductor and dielectric to continue another 70mm
to the top of the Radome (Nylon tube).

I understand the construction of 5/8 antenna but I would not expect the
braid to be earthed.

Thanks in advance for any help.

Regards

David

Dave wrote:
the 4.5 turns is a choke that cuts off the bottom part of the braid from the
top. the top 80mm and 70mm parts are then just a vertical dipole with the
feedpoint at the spot where the braid stops.

I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz.

Which makes one wonder "3dB 'gain'" over what?
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil Moore wrote:
Dave wrote:

the 4.5 turns is a choke that cuts off the bottom part of the braid
from the top. the top 80mm and 70mm parts are then just a vertical
dipole with the feedpoint at the spot where the braid stops.

I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz.


Which makes one wonder "3dB 'gain'" over what?

I purchased these a while ago and pulled them apart to see if there was
much involved in making similar units. They stated 3dB but did not
indicate whether it was dBi or dBd.


What are your recommendations for 915MHz omni-directional antenna ?
I want to see what kind of range I can get from a pair of 1 Watt,
spread spectrum data transceivers with oni-directional antenna.


Thanks

David wrote:
I purchased these a while ago and pulled them apart to see if there was
much involved in making similar units. They stated 3dB but did not
indicate whether it was dBi or dBd.

No phasing coils anywhere?

What are your recommendations for 915MHz omni-directional antenna ?

I'm not the person to ask. All I would do is access the
web pages of the antenna manufacturers, like Diamond.
--
73, Cecil http://www.qsl.net/w5dxp

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Could you post pictures on the binaries or email them to me please? I would
like to see this.

Thanks in advance,
Paul.

p.pinyot [at] worldnet [dot] att [dot] net


"David" wrote in message
...
Hi,

I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz.
After pulling the unit apart and studying the construction, I am not sure
what style of antenna this is.

The antenna consists of an SMA plug that has RF178 cable soldered to
centre pin and
it appears earth braid is connected to ground side of plug.

The cable goes up the inside of 1 6mm Nylon tube for 40mm and then
exits the tube and winds around 4.5T. It then enters the tube
again and runs another 80mm. At this point the earth braid is stripped
leaving only the centre conductor and dielectric to continue another 70mm
to the top of the Radome (Nylon tube).

I understand the construction of 5/8 antenna but I would not expect the
braid to be earthed.

Thanks in advance for any help.

Regards

David

"David" wrote in message
...

Hi,

I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz.
After pulling the unit apart and studying the construction, I am not sure
what style of antenna this is.

The antenna consists of an SMA plug that has RF178 cable soldered to
centre pin and
it appears earth braid is connected to ground side of plug.

The cable goes up the inside of 1 6mm Nylon tube for 40mm and then
exits the tube and winds around 4.5T. It then enters the tube
again and runs another 80mm. At this point the earth braid is stripped
leaving only the centre conductor and dielectric to continue another 70mm
to the top of the Radome (Nylon tube).

I understand the construction of 5/8 antenna but I would not expect the
braid to be earthed.

Thanks in advance for any help.

Regards

David


Paul P wrote:
Could you post pictures on the binaries or email them to me please? I would
like to see this.

Thanks in advance,
Paul.

p.pinyot [at] worldnet [dot] att [dot] net



Hi, Paul -

If you have the 2004 ARRL Handbook, the antenna is described on page 20.17
as a resonant feed-line dipole. The figure on that page shows its construction.

If you do not have the handbook, I can scan the page and send it to you.

Regards,
John