Topband: Using Softrock40/Rocky for 160m weak signal DX

[Steve Ireland]

G'day

I spent this evening using a Softrock V4.0 software defined radio and Rocky 
1.41 sofware for weak signal DXing on 1.8MHz CW - and, boy, what a 
revelation!

The Softrock 40 is an experimental  direct conversion receiver, designed by 
a group of SDR enthusiasts lead by Tony Parks, KB9YIG and costs about 
$30.  In combination with the intelligent image rejection provided by Alex 
VE3NEA's free Rocky software, it has an image rejection of about 
90dB.  Rocky provides an full-screen bandscope, offering both spectrum and 
waterfall facilities, and capable of detecting signal levels down to 
nano-volts.

Instead of continually tuning up and down 1800 to 1835KHz, I simply watched 
the DX section of the band on my PC (P4, 3.0ghz) screen and whenever a weak 
signal appeared, clicked on it, and, hey presto, quickly identified 
it.  The signals I was listening to were between S2 and S5 maximum and 
often in slow and heavy QSB - I found the latter made it easy to tune over 
the top of them with my usual Yaesu FT1000, but I could easily see them on 
Rocky's bandscope and couldn't miss them.

The Rocky/Softrock combination was far more effective than the FT1000 for 
this purpose, on the basis that I found at least five stations (weak USA 
and JAs mainly) in the same time it took me to find one on the FT1000.  The 
98KHz tuning range of the Softrock is provided by a M-Audio Delta 44 sound 
card.

In a totally perfect world, it would be nice if the bandscope was a little 
more sensitive - those most sought-after weak ones on 160m are often 
between S2 and S5 and if the bandscope could be configured to read a 
maximum of 60dB, that would make it easier to spot these signals.

On the other hand, Rocky is light years ahead of any other bandscope I have 
ever seen built into/tacked onto a radio - VE3NEA deserves a medal.  The 
polyphase filtering and the solid trace are masterstrokes.

The direct conversion Softrock 40 - modified for 160m with a front-end 
bandpass filter designed by Phil VK6APH - was much easier on the ear than 
the FT1000.  Without the multiple IFs/mixers of the FT1000, the Softrock 
has that great 'connected direct to ether' sound to it - and the 600Hz 
digital filter made CW much nicer to listen to than the dual 500Hz lattice 
crystal filters in my FT1000.

The only flaw of the Softrock I found was that the A to D converter 
overloaded when I turned the gain flat out so that it was comparable to 
that of the FT1000.  After discussions with Phil, a small attenuator ahead 
of the A to D converter would give the Softrock more receive 'headroom' and 
fix this problem.  I should add that I was using a full-size 160m inverted 
vee dipole antenna about 90 feet (27 metres) above ground and had no 
problems with medium wave BC station breakthrough.

Alex VE3NEA, Tony KB9YIG, Phil and the others who worked on this project 
should take a large bow.  I should emphasize that this is an experimenters 
(bleeding edge) product, but as far as I am concerned, the Rocky/Softrock 
SDR combo is in another league for weak signal DXing from the analog radios 
in my shack.

Go and visit VE3NEA's Rocky website to see the possibilities - at 
http://www.dxatlas.com/Rocky/

The Software V4 is no longer available, but a version 5 can be bought for a 
similar price - see http://www.hamsdr.com/Home.aspx

For those who are interested, I can email them the details of the 160m 
bandpass filter.

Vy 73

Steve, VK6VZ







   


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