----- Original Message -----
Sent: Saturday, February 18, 2017 6:37
Subject: [CrossCountryWireless] SDR-4++
dual diversity SDR receiver
Recently we have been asked to design a dual diversity SDR receiver for a
radio propagation research project.
The receiver design was based on two SDR-4+ PCBs using a single oscillator
so that the two SDR receivers were phase coherent.
The receiver has now been dispatched to the customer but following the
workshop tests especially the on-air tests using two antennas the performance
improvement was so surprising we have decided to offer it for general
There is a new web page for the receiver with several screenshots of dual
HDSDR sessions using a vertical and a horizontally polarised antenna. It's
interesting to see how some signals and interference appear on one or the
other antenna. The difference between the two antennas can be quite dramatic
especially during fading where the polarisation of the signal is rapidly
changing due to the ionosphere.
Listening to the combined audio output where both receivers were fed to a
set of headphones was amazing. White noise appears as a wide stereo field
while wanted signals appear in the centre of the stereo image. To hear 40m
stations while the ionosphere changes the polarisation is fascinating, the
signal level remains the same but the noise varies in each headphone as the
AGC in each HDSDR session tracks the signal. You get the sense that you can
feel the propagation changes rather than just hear them.
The web page is: