SDR Protection Circuit

We have seen a number of Kiwisdr radios recently that have suffered serious damage due to one of the following causes;

1. Nearby lightning storms
2. Transmitting into an antenna close the to the Kiwisdr antenna
3. Accidentally transmitting directly into the Kiwsdr

These failures are often uneconomic to repair, resulting in the owner needing to purchase a new radio circuit board. The internal Beaglebone computer is usually fine.

To try and prevent these failures we have designed an SDR protection device using two 50 ohm transformers and a dual TVS (transient voltage supression) diode. It is a small PCB protected by clear heat shrink tubing.

The circuit has a 1dB insertion loss from 0.1-30MHz which will not have any noticeable effect on HF SDR operation. 

It has been designed for Kiwisdr radios but will work with any receiver. 

We have tested the circuit by applying 100W directly into the circuit connected to a Kiwisdr. Neither the SDR protection circuit or the Kiwisdr suffered any damage. If you applied 1kW direct into a Kiwisdr hopefully the protection circuit would fail and protect the Kiwisdr but there are no guarantees at that power level.

This circuit could save your SDR radio from serious damage. It designed to help in an accidental situation. It should not to be used for regular intentional exposure to high power levels.

The circuit is covered in clear heatshrink for physical protection.

The SDR Protector is US$28 including free worldwide postage.

These will be posted in a letter envelope which normally takes 1-2 weeks to arrive but can sometimes take up to 4 weeks. The letter is untracked but we have been sending other items like recovery SD cards and USB to 5V cables this way for a year and all have arrived. 

The Post Office here doesn't require any customs declaration on stuff that fits in a letter envelope that is less than 10mm thick and less than 100gm in weight. We have never had any reports of customs problems or charges at the customer end.