PA8W Amateur Radio

Wil, PA8W,  E-mail: PA8W@upcmail.nl           
Back

A fixed dual (2m/70cm) Array (144-146MHz + 430-440MHz)


Combining two different size arrays is extremely difficult since the biggest one may have a big impact on the radiation pattern on the smaller one.
The easy approach is: Put up a VHF and a UHF array on separate masts at least a few meters apart.
But for most hams this is not practical, they would prefer to have one single RDF mast instead.
So I studied on reducing mutual influence between the VHF and UHF array and the found that a vertically spaced arrangement would do very nicely:




Looks promising, so I built it:





First of all a look into the  VHF center pod made from 125mm diameter PVC. The pod has a screw lid as a top.

32mm diameter pipes are being used to for the arms to put the dipoles about 50cm apart, so all4 arms should be around 35cm long measured from dead center.
One piece of pipe is used for two arms, running right trough the pod.
The other two arms are shaped in a way that they fit onto the first pipe so they can be glued together using hard PVC glue.
Holes are drilled for the coaxes, for a center bolt and the connectors for the downward running cables are already in place.

2mm holes at the lowest spots are meant to drain  condense water.













A PCB board is used to hold the connectors for the UHF array cables, and a combiner PCB with L/C series bandfilters is glued on top.

A center 8mm bolt runs down to a 50x50x80mm aluminum L-profile to offer a sturdy mast fixation.


Note that the coaxes for all 4 arms are equally long!


And this is how the bottom end looks.

Cups are used to  prevent water from dripping into the connectors.

Note the small 2mm drainage holes in arms and bottom.

This is the top screw lid with the glassfiber vertical spacer rod in place.

And Polymax filler is used to add stiffness to the vertical spacer fitting.

Now the smaller UHF pod is made.
Downward going coax and control cable are running through the vertical spacer rod.

In the lower end of the spacer rod a ferrite ring is  added to uncouple the vertical cable run a bit.

This UHF pod also has a screw lid on top.

A look into the 32mm end caps  that hold the (2x) 50cm long VHF elements.

I made a wooden frame with nails that hold the elements straight in line whilst soldering them.

The elements are made from 2mm steel wire covered with heat shrink tubing.

The PCB is glued at the bottom using Polimax.

This is a UHF dipole.
No end caps here, but oversized tubing to hold the PCB and antenna rods.
After testing, the open end is sealed using Polymax.
\

This is the schematic of  both antenna array's.
For the RDF41 stick to this schematic.
Note that for UHF the inductors may be decreased to 470nH, and on VHF simple 1N4148 diodes may be used.

Both arrays could be coupled into one single coax using a duplexer coupler.
For narrow band 2m/70cm two simple series L/C networks will do the trick.
Both arrays may be driven simultaneously by the Radio Direction Finder, so you need only one CAT-5 control cable.

Right-Mouse-Click on the drawing, and choose "Save as" to save the drawing to your map or desktop.
The resolution will be doubled compared to the drawing on this page. 


73, Wil.


Back