Today’s post is a tribute to the ingenuity and skills of Jim VE6JF. He designed this ultimate antenna switch to eliminate RFI from microcontrollers.
My biggest challenge in building a dual channel antenna switching system for my diversity receivers is Arduino RFI ingress. While a handy device, the Arduino generates a ton of radio frequency interference, both radiated and conducted. My friend Jim Leslie took pity, either on me or my situation.
He was playing around with a bunch of Songle SPDT 5V relays. After studying my requirements, VE6JF designed, milled and built a multipurpose antenna switch, shown above. His printed circuit board is designed in KiCAD and isolation milled on his CNC. Populated with 8 Songle relays, it operates in two configurations, which I describe below.
Jim’s switching board is mounted in a plastic case. Everything is shielded with copper tape and ferrite bead feedthrough filters. How well does this setup eliminate RFI?
Well, we can attach the relay controller Arduino and place the Arduino on top of the box cover, which is also shielded (not shown). Across all of HF, there is not a single drop of measurable RFI. Pretty amazing.
Port isolation is 90 dB. Jim achieves this by placing three relays in series. Insertion loss is negligible and SWR is flat. Now you know why I call this the ultimate antenna switch for diversity reception. But wait, there’s more!
Ultimate Antenna Switch Configurations
You may have been wondering why there is a DIP switch in the middle of the board. You can use this switch to achieve two very different configurations, as shown below.
In configuration A at the right, you can feed one antenna channel to any of four receivers. On the other hand, if I use configuration B at the left, I can route two pairs of antennas to each channel, one at a time.
So, three of these boards are all you need to route your loop array and other antennas to four different diversity receivers. You have complete port isolation and freedom from microcontroller RFI.