KiwiSDR V2 SDR Protection Circuit

The KiwiSDR V2 SDR Protection Circuit is designed to safeguard KiwiSDR receivers—and virtually any other SDR—from the most common and costly sources of front‑end damage. Many KiwiSDR owners have experienced failures caused by nearby lightning storms, transmitting into an antenna positioned too close to the KiwiSDR antenna, or accidentally transmitting directly into the receiver. The original V1 protection circuit provided solid protection against static discharge and nearby lightning, but it did not always survive accidental high‑power RF transmission. The V2 design directly addresses this.

The upgraded V2 unit adds a replaceable 100 mA fast‑blow fuse, providing an additional sacrificial layer of defense for your receiver. A spare fuse is included in a small plastic bag—keep it safe, as 100 mA 1808 fast‑blow fuses are not easy to source. The protection circuit is housed under a secure 3D‑printed cover held in place with a 1.4 mm screw for easy access.

Fuse behavior has been validated during testing: the fuse opens in about 2 seconds with 1 watt, 1 second with 10 watts, and instantaneously with 100 watts. The onboard signal diodes also clamp excessive voltages from the RF transformer, further protecting the SDR input stage.

For best performance, proper grounding is essential. The back‑to‑back switching diodes may not operate correctly if the RF input and ground share the same potential—a condition that can occur with antennas lacking a proper ground reference, such as dipoles. The KiwiSDR 2 enclosure is internally grounded, so attaching a ground wire beneath one of the enclosure’s screw terminals is sufficient. Recent radios even include a ring terminal specifically for this purpose.

If the fuse blows, inspect your station setup to determine what went wrong before replacing it. The fuse can be tested with a multimeter on the Ohms range; a good fuse typically reads around 2 ohms. To replace it, gently pry the blown fuse from the holder using a small screwdriver.

The KiwiSDR V2 SDR Protection Circuit provides robust, field‑tested protection and peace of mind—whether used with KiwiSDR units or any other sensitive receiver.