Re: [IRCA] The "mystery" of 1710khz

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Monday 23 January 2006 17:23, Les Rayburn wrote:
> Barry,
>
> Which software do you use to determine carrier offsets? And
> can I also ask you the settings that you've found to be most
> useful?

The usual procedure is to put your receiver into USB mode and tune it to 
exactly 1 kHz below the nominal carrier frequency (i.e., 1709 kHz in this 
case).  Then run the audio from the receiver into your sound card's line 
input (which you're probably doing already for Total Recorder, etc.) and 
use FFT (Fast Fourier Transform) software to display the audio spectrum.
I use a program called baudline under Linux... I think most Windows users 
use one called Spectrum Lab.  If your receiver (and to a lesser extent, 
the A/D converter in the sound card) introduced no errors, then a carrier 
that was exactly on-channel would produce a spectrum peak at exactly 1 
kHz.  If they are off-frequency, the offset can be determined directly 
from the spectrum display.  Since errors do occur in the real world, you 
need to calibrate them out by doing some measurements on stations whose 
frequency is accurately known.  CHU is a local here, so that helps. :-)  
If there is any interest, I can provide a list of some widely-heard AM 
stations that can be used as frequency references.

That's about it... here's a couple of links for more info:
http://www.dxradio.co.uk/mwoffsets/
http://groups.yahoo.com/group/mwoffsets/

> Used to do a lot of this sort of thing for very weak signal
> LF work...amazing stuff. After the KFI carrier stuff a
> couple of years ago, I've long thought this might be
> a great tool for DXing.

Indeed it is... and quite fascinating to "see" stations that you could 
never hope to get audio from.  I've never heard KFI from here, and don't 
expect to, but it was easy to pick out their carrier in the spectrum 
display.  I don't log 'em if I can't hear 'em, but it's interesting 
nonetheless.

Barry

-- 
Barry McLarnon VE3JF  Ottawa, ON

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