Loggings > North American Shortwave Pirate

XFM 6940 DRM 01:39 18Feb13

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Danoman:
XFM doing some DRM testing.

I did have a lock and some audio come thru shortly after I grabbed this screen capture.

Rockpicker:
Nice Catch!

Darn if I did not see this at 6950 but did not recognize it as a DRM sig. Though it might be MARS or someone like that.
I did not know a carrier would show so distinctly in the center of a DRM sig? I'll know better next time.

Thanks for the ID.....

redhat:
Because of the nature of DRM COFDM modulation, I had to modulate the baseband IF as DSB.  I actually used the upconverter from my stereo rig to get the IF up to 6955.  The lower sideband is identical, although its spectrum is inverted.  This method wastes a lot of power (3DB) on a lower sideband that is essentially useless, and the carrier you see in the middle is the LO leaking through the mixer stage of the upconverter.  Because there is no filtering for IF's this low in frequency, the LO and lower sideband fall inside the bandpass filter following the mixer.  I've got rough plans for a filtered converter just for DRM that will fix all of the above problems and yield a "proper looking" DRM signal.  We'll see what my free time yields over the next couple weeks (or months).

Did i mention I still have QSL's from halloween to do yet ;)

Thanks for the reports, guys.

+-RH

ChrisSmolinski:
I noticed this as well on the SDR recording, centered around 6950 at 0140z.

Way too weak to try and decode, unfortunately.

skeezix:
Hope you haven't given up on C-QUAM....  :'(

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