Hi,

I am in the process of building a 4-Element Yagi to operate at 915 MHz.

The design is as follows...
Element Length Distance from REFL
REFL 159mm 0mm
DE 146mm 40mm
D1 139mm 90mm
D2 132mm 155mm

Boom is 12.8mm OD square aluminium (1.6mm wall thickness)
Elements are 6mm solid aluminium rod.

The design was assuming that the elements were to be insulated from the
boom but I am having trouble making small insulators to hold these in
place.
It would be simpler for construction if I could simply drill through the
beam and weld the rods in place or connect via a screw through the
centre of the beam.

The correction factor formula I have found seems to be for insulated
through-beam elements.

Q: Is there a correction factor I can apply to enable me to construct
the antenna in this manner ?

Q: Does the Driven element need to be in the same plane as the other
elements or can it be out of alignment (ie. If I use a small plastic
enclosure to house the balun and make connection to the driven elements,
the elements will not be in the middle of the beam but rather 5mm or so
above the beam).

Q: Is there an alternate design I could use that would be simpler to
construct. (I am looking for around 7dB gain at low angle of radiation -
point to point communications link). Feedline is 50 Ohm coaxial cable,
power is less than 1 Watt.

Hope I have given enough info to evoke some constructive advice, Thanks
in advance for your help

Regards

David

On Wed, 15 Mar 2006 22:17:03 GMT, David
wrote:

Hi,

I am in the process of building a 4-Element Yagi to operate at 915 MHz.

The design is as follows...
Element Length Distance from REFL
REFL 159mm 0mm
DE 146mm 40mm
D1 139mm 90mm
D2 132mm 155mm

Boom is 12.8mm OD square aluminium (1.6mm wall thickness)
Elements are 6mm solid aluminium rod.

The design was assuming that the elements were to be insulated from the
boom but I am having trouble making small insulators to hold these in
place.
It would be simpler for construction if I could simply drill through the
beam and weld the rods in place or connect via a screw through the
centre of the beam.

The correction factor formula I have found seems to be for insulated
through-beam elements.

Q: Is there a correction factor I can apply to enable me to construct
the antenna in this manner ?

Q: Does the Driven element need to be in the same plane as the other
elements or can it be out of alignment (ie. If I use a small plastic
enclosure to house the balun and make connection to the driven elements,
the elements will not be in the middle of the beam but rather 5mm or so
above the beam).

Q: Is there an alternate design I could use that would be simpler to
construct. (I am looking for around 7dB gain at low angle of radiation -
point to point communications link). Feedline is 50 Ohm coaxial cable,
power is less than 1 Watt.

Hope I have given enough info to evoke some constructive advice, Thanks
in advance for your help

Take a look at Ian's site:

http://www.ifwtech.co.uk/g3sek/diy-y...x.htm#BoomCorr

David wrote:
The design was assuming that the elements were to be insulated from the
boom but I am having trouble making small insulators to hold these in
place.
It would be simpler for construction if I could simply drill through the
beam and weld the rods in place or connect via a screw through the
centre of the beam.

The correction factor formula I have found seems to be for insulated
through-beam elements.

Q: Is there a correction factor I can apply to enable me to construct
the antenna in this manner ?

The ARRL Antenna Book has a graph showing the correction needed for
thru-the-beam elements. I can't recall if it is for insulated elements or
not. It's in the chapter on Yagis -- the chapter with all the K1FO yagi
designs.

Q: Is there an alternate design I could use that would be simpler to
construct. (I am looking for around 7dB gain at low angle of radiation -
point to point communications link). Feedline is 50 Ohm coaxial cable,
power is less than 1 Watt.


WA5VJB has some cheap yagi designs, and also sells PC board-based antennas on
his web site.

http://www.clarc.org/Articles/uhf.htm

I built a 902mhz WA5VJB design using a piece of square moulding. If you paint
the boom with primer or polyurethene, it should last some time.

Glen, kc0iyt

On Wed, 15 Mar 2006 22:17:03 GMT, David
wrote:

Hi,

I am in the process of building a 4-Element Yagi to operate at 915 MHz.

The design is as follows...
Element Length Distance from REFL
REFL 159mm 0mm
DE 146mm 40mm
D1 139mm 90mm
D2 132mm 155mm

Boom is 12.8mm OD square aluminium (1.6mm wall thickness)
Elements are 6mm solid aluminium rod.

The design was assuming that the elements were to be insulated from the
boom but I am having trouble making small insulators to hold these in
place.
It would be simpler for construction if I could simply drill through the
beam and weld the rods in place or connect via a screw through the
centre of the beam.

The correction factor formula I have found seems to be for insulated
through-beam elements.

Q: Is there a correction factor I can apply to enable me to construct
the antenna in this manner ?

Q: Does the Driven element need to be in the same plane as the other
elements or can it be out of alignment (ie. If I use a small plastic
enclosure to house the balun and make connection to the driven elements,
the elements will not be in the middle of the beam but rather 5mm or so
above the beam).

Q: Is there an alternate design I could use that would be simpler to
construct. (I am looking for around 7dB gain at low angle of radiation -
point to point communications link). Feedline is 50 Ohm coaxial cable,
power is less than 1 Watt.

Hope I have given enough info to evoke some constructive advice, Thanks
in advance for your help

Regards

David

http://www.wia.org.au/armag/2002/AR_...ionFactors.pdf