444 MHz Stacked Dipoles
Designed by VE3ETK

At the October Meeting Bill VE3ETK gave an excellent talk named "Things You Can Do With Coax"  Here is one project that Bill described.

This antenna exhibits almost 3db gain and produces a horizontal dough nut shaped pattern, making it very useful as an outdoor antenna to increase the signal from your handheld transmitter to local repeaters. Cost: under $15.00. Time: about 1 ½ hrs.

To make the antenna proceed as follows:
USE ONLY RG-8 COAX WITH STRANDED CENTER WIRE AND WOVEN BRAID SHIELD. About 6' of this coax is needed.

Approximately 5' of 1" OD PVC pipe, and one end cap is needed. The end cap needs to be flat (as opposed to rounded) on the top.

One coaxial cable connector is needed that will fit RG-8 coax.

See attached diagram for assistance. (click on drawing for full size image suitable for printing)

  1. Cut off 10" of the coax and carefully slice off the outer jacket. Now, carefully slide back the shield and set it aside.

  2. From one end of the remaining coax (we will hereafter call this the bottom) measure up 18" and cut through the jacket, all the way around.

  3. Measure up a further 6.5" (all of the remaining measurements are critical to 1/10 of an inch) and again cut through the jacket all the way around. Remove the jacket between the two cuts.

  4. From ½" UP on the bared shield cut through the shield, and again at the TOP of this bared shield. Remove all of the shield between these two cuts.

  5. Carefully fold the ½" of remaining shield back over the jacket, towards the bottom and secure it with a bare #20 wire. Take the piece of shield you earlier set aside and carefully slide it up over the coax jacket from the bottom, until it just covers the ½" of shield just folded back and secured. Secure this also with a bare #20 wire, and solder the shields together.

  6. Carefully smooth this section of shield back towards the bottom until it is tight against the coax jacket. Secure the bottom of the shield with a piece of tape.

  7. Measure from the top of this section of shield towards the bottom 6.25", and just barely above that point secure it with a bare #20 wire. Solder the wire and shield. Just below the wire cut off and remove any surplus shield. Bind the bottom of the shield section with tape to prevent any 'creep' upwards.

  8. Picking up now from the top cut made in point 3; Measure up a further 6.5" (this point will now be referred to as Point A) and remove all jacket from this point to the top of the coax.

  9. 1/2" up from Point A cut through the shield and remove it from that point upward. Take the ½" of shield and fold it back over the jacket for the moment.

  10. At Point A cut away ¼" of insulation all the way around and right back to the center conductor. In this ¼" of space, and as close to Point A as possible, wrap one turn of #18 stranded, bare, wire around the center conductor and solder in place. Bring the ends of this #18 wire out and wrap them firmly around the shield that was folded back in 9. Solder as close as possible to Point A and trim away all excess.

  11. From Point A measure up 6.8" and cut away all insulation from here upward, taking care not to cut into the center conductor. Measuring up 1" of the center conductor, cut it off anything beyond that point.

At this time the electronic part of your antenna is finished.

  1. Cut a length of PVC pipe to slide the antenna down into, leaving enough for a coax connector at the bottom

  2. Push the center conductor at the top of your antenna through a 1/8" hole drilled in the center of the top cap. Slide a small brass washer over the bit of center conductor coming out of the cap. Pull the coax up firmly and feather the wires of the center conductor out over the washer. Solder the wires to the washer and cut off any excess.

  3.  Apply PVC cement to the top of the pipe and quickly slide this pipe up the antenna and seat it into the cap.

  4. Apply a liberal coating of epoxy resin to the top of the cap, particularly in the area of the washer. The whole purpose of the pipe and cap is to give weather protection to the coax, and to provide a method of mounting.

  5. Install the coaxial connector to the bottom of the coax, and fill the space around the coax and the bottom of the pipe with weather seal caulking. NOTE: DO NOT USE SILICONE CAULKING AS IT HAS ACETIC ACID IN IT, AND EVEN THE VAPOURS FROM THE ACID WILL CORRODE THE COPPER ELEMENTS OF THE ANTENNA.

The antenna is finished, and you may mount it by using clamps anywhere in the lower 6 inches. I recommend plastic clamps to prevent any interference with the pattern producing segments of the coax.

Questions???  Contact Bill VE3ETK at VE3ETK at RAC dot CA