Automatic monitoring of the signal strength / frequency of CW beacon
signals, including those that drift by a small amount, can be achieved
using signal processing techniqes borrowed from the radar and Comint
worlds. Referred to as CFAR, or Constant False Alarm Rate, the
principle is to take an FFT of the wanted band, then obtain an
estimate of the noise level and all CARRIER type signals present by
using statistical techniques, like averaging over adjacent time
samples, searching adjacent bins and voting.
I described the process in detail in the RadCom Data Column in three
parts over April/June/August 2008 and it also appears in "Command" [
http://www.rsgbshop.org/acatalog/Online_Catalogue_Computing___Radio_39.html
(still some copies left at bargain prices:) ]
The S/N of any carrier that exceeds the noise level by a certain
minimum amount can be determined accurately by the monitoring process,
its frequency determined and drifting signals can be tracked.
Multiple carrier s can be tracked if needed The process does not work
so reliably where signals are modulated, so clearly are not of much
use for situations where the beacon callsign etc is not known in
advance. However, it can be made to work sucessfully on the
microwave bands, where beacons freqeuncies and locations are known in
advance.
Microwave Beacon Monitoring software using CFAR techniqes and
including all source code can be found at :
http://www.g4jnt.com/dspsw.htm
with an overview at http://www.g4jnt.com/UWBCNMON.pdf
This particular software is too wideband for LF use, but the code
could be modified for lower sampling rates and bandwidths, and used
for auto monitoring of QRSS signals, once their origin has been
determined by other means
Andy G4JNT
www.g4jnt.com
2009/1/27 Rik Strobbe <[email protected]>:
> Hello Klaus,
>
>> On the other hand, WSPR has the advantage of automatic
>> recording. But that is not an advantage of the mode, it
>> simply is the lack of a corresponding simple program that
>> does the same with a QRSS signal.
>
> the automatic recording/reporting ability is clearly an advantage of WSPR in
> regard with propagation studies. And I agree that QRSS or DFCW would serve
> as well or even better if a similar automatic recording/reporting would be
> provided.
> But I am afraid that a "waterfall display to ASCII" conversion is not simple
> at all ;-)
>
>> Nevertheless, WSPR is not very near to the Shannon limit.
>> I spent nearly all my leisure time of the last year with
>> the design of a new digital ham radio QSO-mode HD43 that
>> comes as close as possible to the theoretical limit.
>> I will send a preprint on request.
>
> I am interested
>
> 73, Rik ON7YD - OR7T
>
>
> Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
>
>
>
|
