How to Build an Antenna Selector Switch

Date:2014/11/17 11:36:00 Hits:

When you first looked at the Heathkit or Hallicrafters ham radio kit you got for your birthday years ago, you were hooked. Since then, you’ve probably cobbled more than one piece of ham gear together. Now, you find that you need to switch between two antennas. You can buy an antenna switch box, but if you have some spare bits and pieces, such as coaxial sockets or a junction box, hanging around, you’ll have the satisfaction of having done it yourself, once again. You can even add a frequency counter.

Things You'll Need

    2-mm silver-plated wire
    Wire cutters
    Three SO239 coaxial sockets
    Soldering pencil
    Silver-bearing rosin-core solder
    Junction box, bottom knockout, three knockouts per side

    BNC connector
    10-pF capacitor
    220-pF capacitor
    Three-position slide switch
    Junction box faceplate (slide switch)
    Frequency counter

Instructions

1.Cut four pieces of 2-mm silver-plated wire, each half as long as the junction box's longest dimension, using wire cutters.

2.Solder one end of each of the three 2-mm silver-plated wires to the lug on each of the three SO239 coaxial sockets, using a soldering pencil and silver-bearing rosin-core solder.

3.Remove the center knockout on one side of the junction box. Remove the nut from one of the coaxial sockets. Anchor the socket in the center knockout, to serve as the transmitter socket. Install a BNC connector in the knockout on the bottom of the junction box.

4.Solder one of the 10-pF capacitor's leads to the lug of the transmitter socket at the center knockout position. Solder the other lead the lug of the BNC connector. Solder one lead of the 220-pF capacitor to the lug of the BNC connector.

5.Solder the remaining lead from the 220-pF capacitor to the side of the junction box.

6.Install two SO239 coaxial sockets in the knockouts on the side of the junction box that's opposite the transmitter socket. Looking at the face of the junction box, the upper coaxial socket is the Antenna 1 socket and the lower is the Antenna 2 socket.

7.Solder the silver-plated wire attached to the Antenna 1 socket to the upper-end lug of the 3-position slide switch. Solder the wire attached to the Antenna 2 socket to the lower lug of the slide switch.

8.Solder the wire from the transmitter socket to the center "hot" lug of the slide switch.

9.Install the slide switch into the junction box, using the screws provided with the switch and a screwdriver. Install the faceplate on the junction box, using the screws included with the junction box.

10.Install the coaxial cable from antennas 1 and 2 to the antenna output sockets. Install the coaxial cable from the transmitter into the transmitter socket. Install a frequency counter into the BNC connector.

Tips & Warnings

    The capacitors create a capacitive voltage divider. In 10-meter service, the voltage divider improves the standing wave ratio, as it becomes a suitable noise filter for that frequency.

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