Fw: *****SPAM***** [softrock40] Dual-receiver Rocky

Terry Fox wb4jfi at knology.net
Mon Jan 1 10:02:28 CST 2007

This also looks very interesting.  Paul and I discussed diversity reception while I was in DC.  I didn't know that Alex was back working on Rocky, so that's great!!  I hope he messes with transmit while at it.

This and Phil Covington's HPSDR Rx board (and forthcoming Tx board) are items to watch.

----- Original Message ----- 
From: Alex, VE3NEA 
To: softrock40 at yahoogroups.com 
Sent: Sunday, December 31, 2006 1:33 PM
Subject: *****SPAM***** [softrock40] Dual-receiver Rocky

Phil.VK6APH, Steve VK6VZ and I have been playing with a dual receiver system 
for some time, using an experimental version of dual-channel Rocky software, 
Rocky 2.0. This version of Rocky is designed to work with two 
phase-synchronized Softrock receivers. It has two independent I/Q balancers, 
two identical filters, two AGC units, etc.

Two diversity reception modes are available in the program. In the binaural 
mode, the signals from two receivers are processed independently and sent to 
the left and right channel of the output audio card respectively. In the 
linear combination mode, the second signal is scaled and phase-shifted 
according to the user settings, and the sum of two signals is sent to the 
sound card as mono audio. The dual-receiver mode is activated automatically 
if the sound card selected as input device has 4 channels. If a 2-channel 
card is selected, Rocky 2 works just like Rocky 1.x -- that is, in the 
single receiver mode.

There are also a few changes/additions in the single-receiver mode:

- a simple but efficient impulsive noise blanker;
- a slow waterfall display optimized for the CW mode. This display allows 
detecting very weak signals long before they can be heard;
- a work around the bug in some audio drivers. Some sound cards that did not 
appear in the device selection list are now recognized correctly by Rocky.

Rocky 2 is still work in progress, the latest executable is available at 
http://www.dxatlas.com/rocky/rocky2.zip . Install Rocky 1 first, then 
replace the old Rocky.exe file with the new one.

I am playing with two 40 m SoftRocks v.6.1 built and phase-synchronized by 
Phil. The first antenna is a dipole at 30 ft, the second one is the HF-2V 
vertical. This setup proved to be an efficient QSB killer. I have made a 
couple of stereo recordings in the binaural mode and uploaded them to
http://www.dxatlas.com/rocky.BinauralWav.zip. Qsb.wav is a recording of weak 
signals with deep QSB. Instead of fading in and out, the signals just pan 
from right to left and back but never disappear in the noise. The other 
recording is a pileup. The signals appear to be coming from all directions, 
creating a full impression of a 3D scene. Use the headphones to listen to 
these files, the speakers cannot give you the true binaural effect.

The linear combination mode is intended for beam forming. It can be used to 
either add up two signals in phase and improve the SNR if the noise is 
ambient, or to null a single source of strong local noise. The phase and 
gain ratio can be set by clicking on the phase/gain diagram that opens in a 
separate window in the dual-radio mode. I have not been very successful so 
far in using this mode, probably because the vertical patterns of my 
antennae are too different. It would be interesting to try two identical 
antennas. An example of local noise nulled in this mode is at 
http://www.dxatlas.com/rocky/NoiseCncl.wav : the first half of the recording 
is made with noise nulling disabled, then the function is turned on.

73 and Happy New Year,

Alex VE3NEA 

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