Remote Antenna Switch
Note: The relays used in this design are no longer available from DX Engineering.
My antenna tuner started flaking out on me so I decided to put up an 80 meter vertical. Since the height of the closest accessible tree limb was just over 40 feet high, I needed a design for a short vertical. I settled on IW5EDI’s design at iw5edi.com. I cut everything long and started pruning and ended up with the vertical wire being 40 feet and each arm of the hat at 20 feet. Resonance is around 3.61 mHz and my TS-440S-AT can tune the entire band. The SWR is less than 3 over the entire band, surprisingly good for 80 meters. I built a choke out of about 6 coils of RG-213 wrapped around a 4 inch PVC pipe. My first contact was Bosnia, not bad for 100 watts into a 12 gauge wire buried in the foliage. Later that night I quickly worked 30 stateside stations in a CW contest. So far I’m very pleased.
Of course now I have two antennas and no convenient way to switch them. After many hours of research, I settled on a design loosely based on DX Engineering’s 8 Port Remote Antenna Switch. DX Engineering sells the 5 kw relays (see: http://www.dxengineering.com) so I designed a 4 port switch around them. I have a wonderful extruded aluminum box I wanted to use, but the maximum PC board size is 5″ x 1.75″. I had to place the SO-239 connectors on one board and the relays on the other. The relay board is soldered to the back of the connector board on short standoffs. The connector board has an RJ-45 jack so the controller is connected to the switch with essentially a 100 foot long Cat-5 patch cable.
Here is the artwork for the two PCBs followed by the schematic. Click on the photos for full size image. If you would like the original PCB image created with Photoshop, click HERE. For a full sized 600 dpi JPEG right-click HERE and select “Save Target As…”. If you print the JPEG image, make sure the image prints 8″ x 10″ @ 600 dpi. When you position the mylar over the unexposed PCB, make sure the words are not reversed.
It has been a few years since I etched a circuit board so I had to re-learn the process. I found the best prices for pre-sensitized circuit boards at Circuit Specialists. I printed two copies of the circuit pattern on my laser printer onto overhead transparency mylar and aligned them on top of each other to get a darker pattern. I exposed the boards through the mylar for 10 minutes, 6 inches below my wife’s Ott light (2 small “daylight” fluorescent tubes) and they came out beautifully. I did test patterns at exposures ranging from 5 to 16 minutes and could barely tell the difference. Since the circuit boards don’t have plated through holes, you will have to drill and run wires through the board in places, but I laid out the artwork to minimize this.
Here is the completed assembly showing how the two circuit boards are sandwiched together. The SO-239s are mounted to the first PCB using 1/4 inch standoffs. Note the MOVs soldered directly across the relay coils.
And finally, the completed 4 Port Remote Antenna Switch mounted to a 4×4 post and connected to two antennas.
The control box in the shack consists of a 5 position rotary wafer switch (off and antennas 1-4), and 4 LEDs that indicate which antenna is selected. With different switching you could select more than one antenna for a phased array.