Tagged: MFJ-1708SDR

Demonstrating the MFJ-1708SDR Automatic Relay Switch with an SDRplay and Icom IC7300

A few weeks ago we posted about the MFJ1708SDR automatic relay switch and how it can be used to combine an RX only SDR with a transmit capable radio. An automatic antenna relay switch is used to automatically ground the SDR's antenna input whenever the TX capable radio transmits in order to protect the SDR's front end from blowing up due to high TX power.

In this YouTube video Pete Sobye shows us the MFJ1708SDR working together with an Icom IC7300 HF radio and an SDRplay which is being used as a panadapter. For software Pete uses HDSDR and Omnirig which allows the PC to control the IC7300.

Using a Transmit/Receive Switch to Protect an SDR from a Transmit Radio

A question that comes up often is how to combine an RTL-SDR, or any other RX only SDR with a transmit capable amateur radio. It's not possible to connect the RX only SDR together with the TX radio via a standard splitter because the TX radio's power will most likely blow up the SDR with it's powerful output. To solve this problem you need either a manual switch that will switch out the SDR when transmitting which requires absolute discipline to not accidentally transmit in the wrong switch position, or an automatic relay switch.

Over on YouTube channel HamRadioConcepts has given a good overview and demonstration of the MFJ-1708SDR Transmit/Receive automatic relay switch, which is a good product that solves this issue. It is also a fairly budget friendly option, coming in at only US$79.95 over on the MFJ website. HamRadioConcepts notes that the switch automatically grounds out the SDR whenever the PTT on the radio is pressed, and also has a fail safe that will automatically detect a transmission and ground the SDR if PTT is disconnected.