Modifying Conifer Antennas for Wireless Networking part 2

Antenna Disassembly
Start by disassembling your Conifer antenna.
Remove the 2 or 4 bolts which attach the mounting bracket and the feedhorn to the dish.

Remove the reflector from end of the feedhorn by removing the small screw in the centre of it.

remove the screw holding the reflector onto the feedhorn
Remove the nose cone from the feedhorn. Some people have reported being able to remove the nose cone after cracking the glue with a hammer and screwdriver.


cutting the nose cone
I normally use a hacksaw to cut along the join to remove the nose cone from the feedhorn. Other people have reported carefully squeezing the end of the feedhorn in a vice will crack the glue, allowing the nose cone to be removed.


the feedhorn with the nose cone removed
Remove the nut and washer from the base of the feedhorn, and remove the down-convertor from the feedhorn.


remove the nut & washer at the base of the feedhorn

the down-convertor
A hammer may be necessary to persuade the down-convertor to separate from the feedhorn.

Separate the metal feedhorn base from the plastic body of the feedhorn, and remove the sticky glue residue using mineral turps.


remove the sticky glue residue
You'll have to drill out the feedhorn base to approx 10-11mm in order to be able to fit the coax through it.
Secure the feedhorn base in a bench vice, and carefully enlarge the hole until you can fit your chosen coax through it.


drilling out the hole in the base
I found a 10mm masonary drill bit at very slow speed works quite well.

Dipole Construction
Start by cutting off a 50mm length of copper pipe, and cut some slots in one end, making the length of the slots as close as possible to 30.5mm.


cutting the slots
Clean up the slots with a small needle file (for the car buffs, a points file works quite well too).

Clean up both ends of the pipe with a file, and use some sandpaper to clean up the external surface of the copper pipe. Also cleanup the inside of the copper pipe (the cut end, as you'll need to solder it, and the other end to ensure a good connection to the coax braid.


cleaning up the copper pipe
I clean up the pipe by holding it in the chuck of my drill (holding the drill on the workbench), and then using sandpaper and a file on the rotating pipe.


the completed copper pipe with slots
Cut off 30.5mm of the small brass tube to make the balun, and clean up the ends with a file.
Using a small drill bit, drill a hole near one end of the brass tube. This hole will make it easier to solder the coax core into brass tube.


the hole in the balun
For the dipole, we used some brass plate, approx 12mm wide by 61mm long. The length of the brass plate isn't too critical just yet, as long as it's at least 61mm long. It'll be trimmed to the correct length once the parts have been soldered together.
Mark the centre of the brass plate, as this is where you'll have to solder the small brass pipe.


mark the centre
Then hold the copper pipe against the brass plate (with the slotted end against the brass plate), and mark it's location.


mark the location of the copper pipe
Then hold the copper pipe against the brass plate, and mark it's location


mark the line to cut
Now cut the brass plate along the blue line, and clean up the cut ends with a file. I find a junior hacksaw works quite well for this.


the brass plate after being cut
Clean up the cut edges, and remove the tarnish with some sandpaper.


the polished brass plate
We've used both RG-213 and CNT-400 coax for these modifications, and they require slightly different approaches to the coax core.
Note that CNT-400 or LMR-400 is recommended, rather than RG-213, due to the lower impedance.

Strip approx 30mm of the black outer sheath off the coax.


RG-213 coax with the outer sheath stripped off
Fold the braid back over the remaining outer sheath.


the braid folded back
Strip off the central insulation, and if using coax with a stranded core (ie, RG-213), double each strand of the core over, and tighten up the bends with a pair of pliers.


the core folded over
Fit the brass tube over the coax core, with the hole previously drilled being located closest to the coax. Solder the brass tube to the coax core, using the hole to supply solder onto the join.


the brass tube soldered onto the coax core
Push the copper pipe over the folded-back braid on the coax, until the brass tube protrudes past the end of the copper pipe by at least a few millimetres.
Note that you may need to un-braid the coax braid, to as it is a pretty tight fit.


the copper pushed onto the coax
Tin the two pieces of the brass plate where they need to be soldered to the brass tube and the copper pipe.


the tinned brass plate
Tin the end of the brass tube and the end of the copper pipe with some solder.
Solder the brass tube onto the previously marked centre point on the larger of the two brass plate halves.


the brass tube soldered to one half of the dipole
Now slide the copper pipe down against the brass plate, and solder it to the brass plate, ensuring the two slots are aligned against the long sides of the brass plate.


the copper pipe soldered to one half of the dipole
Solder the other half of the brass plate to the copper pipe, ensuring there's an air gap of approximately 1mm between the two brass plate sections.


the assembled dipole
Measure the overall length of the brass plate, and trim the length to make it 61mm long. This is the dipole, and its length should be as close to 1/2 wavelength as possible.

Using the original dipole as a template, measure, mark and drill the the holes in each end of the dipole. These holes are used to locate and hold the dipole in the feedhorn.

If you've got access to a coax crimper, use it to crimp the copper pipe onto the coax braid, to ensure a very firm connection, and trim the excess braid which is still protruding past the end of the copper pipe.


two holes drilled in the dipole,
and the copper crimped onto the coax


navigation: part 1 | part 2 | part 3

Posted By Sameera Chathuranga

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