Ah there's one detail I forgot to mention, which may
better answers your question: The software procedure which estimates
the carrier bandwidth first applies some variable smoothing to
the power spectrum. The smallest used smoothing window is 5 FFT
bins, which then translates into different mHz bandwidths (1.2 mHz at
Op-64, 2.5 mHz at Op-32, 5 mHz at Op-16). Even when the carrier has
been ideally narrow in reality, the display can hardly be less than
that.
73, Markus
Sent: Wednesday, December 18, 2013 12:50 AM
Subject: Re: LF: 136 Dial freq for OP-OPDS 32 for
tonight...,
Bob,
the bandwidth displayed by opds is supposed to tell
you the width of the central carrier, it's ideally zero and not related to
the modulation speed. A stable and coherent signal like yours usually
shows 1 or 2 mHz, but the figure surely won't be good
to the last digit. The carrier is only present when
the transmitter is being keyed with phase continuity from dash to dash, and
it can then be used by opds as a phase-reference for synchroneous AM
demodulation.
On the other hand, the conveyed keying
information resides in the AM sidebands around the carrier, with a
width proportional to the inverse dot length. In Hartmut's Op-16
(4 second dots) capture, we find about 0.2 Hz wide main lobes on each side of
the carrier. Due to the "unspreading" effect of the correlation, opds can still
retrieve the most likely callsign even when the power density of the
sidebands is well below the noise.
Best 73,
Markus (DF6NM)
Sent: Wednesday, December 18, 2013 12:13 AM
Subject: RE: LF: 136 Dial freq for OP-OPDS 32 for
tonight...,
Markus; Was wondering why my bandwidth was over twice as high as
usual last night on 73 band OP16? Must have something to do with faster
OPERA mode? And looking at my signal on Hartmut's grabber was what
appeared to be digital data on each side of the carrier. Wonder what would
cause those sidebands as I understand OPERA is nothing but keyed CW with no
modulation-unless it was hum on my carrier? Bob
From: [email protected]To: [email protected]Date: Tue, 17
Dec 2013 23:59:41 +0100 Subject: Re: LF: 136 Dial freq for OP-OPDS 32 for
tonight...,
Bob, Alex,
welcome again!
2013-12-17 23:03:34 WE2XEB 6448km
137540.999Hz 2mHz -47.7dBOp 76% 15.5dB
2013-12-17 23:03:07
R7NT 2060km 137590.028Hz 4mHz -42.4dBOp 77%
17.0dB
73, Markus (DF6NM)
Sent: Tuesday, December 17, 2013 6:53 PM
Subject: LF: 136 Dial freq for OP-OPDS 32 for
tonight...,
WE2XEB NY will be on at 2200 or so with OP/OPDS 32 tonight at 136
dial freq 137.541 TX freq as of now-all decodes appreciated-Bob
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