New version of Receiver Protection Unit

Chris Moulding

We have released a new version of the Receiver Protection Unit so that the maximum output is below the strict 10 dBm limit for SDRPlay receivers.

In the previous version the maximum output level was 17 dBm which is OK for the majority of receivers but was still too high for SDRPlay receivers.

The protection unit uses a range of methods such as a gas discharge tube, isolation transformer and cascaded diode limiters to bring excessive RF power down to a safe level.

If connected to a ground it will also drain static electricity from the antenna and a 10 kA gas discharge tube will help with nearby lightning strikes.

With the latest version you could connect a 150 W transmitter for that ham radio "Oops!" moment without exceeding the SDRPlay receiver limit.

More details on the web page:



Chris Moulding

OK it's official.

SDRPlay have approved the VLF/HF Receiver Protection Unit as recommended for use below 50 MHz with SDRPlay RSP receivers.

I've added the change to the web page:



Roger Need

The factor not often mentioned in the specs for receiver protection boxes is the OIP2 and OIP3.  In order to do the limiting they all contain some type of non-linear limiting device (diode, saturating transformer etc.) and these generate unwanted spurious signals.  This happens at signal levels well below the maximum output limit spec of 10 to 20 dBm.

The OIP2 and OIP3 two carrier tests will give an indication of what to expect when you use one of these protection devices.  Perhaps Chris will let us know what he measures on his unit.