My Projects......

Automatic Antenna Switch


As I am so lucky as to have a tuned antenna for each amateur band between 80M and 6M I thought that an automatic antenna switch would be very convenient. There is only one coax cable running from the shack to near the base of the (Versa - 18M) tower. There I mounted a remotely controlled antenna switch that can switch between the following antenna's:


* 80M half wave - inverted V - dipole,

* two 40M half wave slopers,

* a half wave dipole for 30M,

* the 3 el SteppIR yagi.

* and the 160M dipole (N/A yet...)


The "remote" unit is connected to the control unit by a 9 strand computer cable (using waterproof DB9 connectors). The strands are a bit thin (cable is 7/0.12 * 9), but even with the heavy duty relays there is only about 100 mA current and only one relay switched in at the time. The total resistance over about 30M cable (both signal and ground wire together) is 12 ohm so we loose 1 Volt.

remote antenna switch


Click on the pictures to view them in a larger format.

Remote antenne switch control unit

This is a picture of the control unit. It has its own regulated and filtered power supply. The left hand PC board is the EA4TX ARSWIN Rotor Control Board that hooks up with my rotor and logging program. The central (VERO) board is the band decoder and driver unit for the antenna switch. Right is the power supply (13.5V - 0.5 amp regulated).

On the front panel from left to right

  • auto/manual selection for the antenna switch
  • antenna selector for 40M (two positions)
  • leds indicating which antenna is selected
  • manual antenna selector switch
  • on/off Rotor controller
  • Power on/off

The band decoder was developed after a design by Microsystems. The schematic of this design is available in PDF format. However, I made several changes. The series resistors on the led side of the Opto Couplers should be left out (especially when using 4N26 in combination with a Yeasu FT1000MP. The FT1000MP already has 1K resistors in the BCD output (Band Data socket) and with the extra series resistance the Opto Couplers do not "couple" well.

Further I used a ULN2804 which has one extra output. Not used yet but one never knows.... There are still two unused wires in the cable and space for two more relays one the board in the box.

I also combined 20M and all higher bands to one antenna (with diodes on the Q5 - Q9 outputs of the MC4028). The 40M output (Q3) is "split" over two ULN2804 driver ports to enable the selection of two different antenna's. With a push button on the front panel I can switch between my long path sloper and short path sloper.

In my previous antenna switch I had some problems with RFI (two channels switching at the same time in the rhythm of my CW....) But with the CMOS levels this seems to be a thing of the past. There is still RFI on the rotor control unit however. Any ideas....????


The "remote" unit is simple a collection of industrial grade (380V 30A ) relays in a die cast aluminium box. Of course with the necessary suppressor diodes (not really necessary with the built in diodes in the ULN2804 package) and 0.01 capacitors. I used N connectors because they have better weatherproof characteristics than PL259 and I live close to the ocean....


Sorry folks... I usually do not make a schematic for my projects but work off the data sheets and put things together that way. So there is no schematic. Just the above description of how I put it together.

If you are interested in one of my projects, the components used or more details than given on these web pages you are welcome to contact me. Please feel free to use the web mail facility on this web site.

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