ARLA/CLUSTER: SDR-4++ - Um novo desenho de receptor para projetos de pesquisa de propagação

[João Costa > CT1FBF]

SDR-4++ dual diversity SDR receiver

Recently Cross Country Wireless 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 sale.

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 SDR-4++ web page is:
http://www.crosscountrywireless.net/sdr-4_plus_plus.htm

Our main web page is:
http://www.crosscountrywireless.net