Sunday, November 24, 2013

It's Not You -- VOA Images Sent Slanted

The VOA Radiogram images for November 23 and 24 were sent at a speed considerably different from that in the original program.  Kim Elliott does not know the cause of the problem yet, but everyone's receiving them that way.  It's not you.

He has several ideas on how to get an accurate copy:

Merkouris Gogos in Greece sent correct images, but this is what he wrote:

"The +180 ppm sample rate correction value, which was working for months, had to be changed to -2080 ppm!"

I tried the same from my recording of reception via the University of Twente SDR receiver, and had to set the ppm correction to -2400 ppm.

For reception the rest of this weekend, I would recommend that you start with Merkouris's parameters.  In Fldigi: Configure > Sound Card  > Settings > under Corrections set the RX ppm to -2080. 

If you can record the broadcast, then decode from the recording, you can try various corrections to see what provides you with the straightest images.

Since the last broadcast is just now airing at time of publication, it may be too late to get a recording. Worry not:

If you want to decode from the "studio" recording of this weekend's broadcast:

But set the RX ppm back to 0 (zero), because the recording seems to be OK.

Other people have tried changing audio playback speeds (if you can do that).  Otherwise, the correction in Fldigi is different for every setup, and seems to be somewhere around -2000 to -2100.  (Kim's -2400 probably had to do with latency in the remote Internet receiver.)

It might be worth checking to see how others are doing.

Thanks to Kim Andrew Elliott at VOA for this information.


UPDATE: The images displayed properly here with a correction of -2340 ppm. This is using the WiNRADiO Excalibur Pro with Virtual Sound Card.