On VOA Radiogram, 7-8 December 2013, we will conduct one follow-up experiment from the previous weekend. We determined from that program that text in the MFSK64 mode centered on 1000 Hz, thus 500 to 1500 Hz, was not affected by the overlapping second harmonic at 1000 to 3000 Hz. The MFSK64 image that was centered on 1000 Hz showed some horizontal interference lines. Did the harmonic cause those lines? We’ll find out by transmitting that same picture in MFSK64 centered on 1500 Hz, then 1000 Hz.

The problem with slant in the MFSK images appears to have been solved. Nevertheless, at the beginning of the program, we will transmit a vertical line. In Fldigi, have the Configure > Sound Card > Settings box open to make any necessary adjustments while that line is transmitted.

There will be two VOA News stories in the robust MFSK32 mode this weekend. This will help cope with difficult reception, such as European listeners experienced last weekend on 15670 kHz.

Here is the lineup for VOA Radiogram, program 36, 7-8 December 2013:

  1:37  MFSK16: Program preview (2:32)
  4:10  MFSK32: Slant alignment (1:34)
  5:42  MFSK32: Capitol Christmas tree, with image (3:20)
  8:48  MFSK32: Water on exoplanets, with image (5:50)
15:06  MFSK64: Image at 1500 vs 1000 Hz center frequencies (4:51)
20:06  MFSK64/Flmsg: Radio signals and space debris, with image
            (5:01)
25:09  MFSK32: Closing announcements (:43)      

Please send reception reports to radiogram@voanews.com 

VOA Radiogram transmission schedule
(all days and times UTC)
Sat 1600-1630 17860 kHz
Sun 0230-0300 5745 kHz
Sun 1300-1330 6095 kHz
Sun 1930-2000 15670 kHz
All via the Edward R. Murrow transmitting station in North Carolina

VOA Radiogram listener Aldo Laddomada is technical director of FM radio station Radio Centro in Locorotondo, Italy.

On 1 December, he transmitted the “studio” wav file of VOA Radiogram, number 35, on Radio Centro.

As expected, the MFSK images decoded from that FM transmission were perfect:

2) Our experiment with audio harmonics found virtually no difference between the 1500 Hz and 1000 Hz center frequencies for both MFSK64 and MFSK64L. With a center frequency of 1000 Hz, the second harmonic (1000 to 3000 Hz) overlaps the fundamental (500 to 1500 Hz), but this overlap appears not to have had any negative effect on decoding.

Lorenzo, IZ0KBA, produced this YouTube video from his reception on 30 November 2013 at 1600-1630 UTC on 17860 kHz:

http://youtu.be/d-aHkMLurEo

Tim, K0RUS, in Colorado provide this video of his reception, same day and time. Note that Lorenzo and Tim, about 10,000 km apart, are hearing the same transmitter on the same 17860 kHz frequency:

http://youtu.be/-8yjAPO7NqU

Marco, IK0DWN, also near Rome, produced this YouTube video based on his reception 1 December 2013 at 1930-2000 on 15670 kHz. As we near the winter solstice, reception of this frequency in Europe becomes more difficult, but the MFSK16 and 32 modes provide 100% copy:

http://youtu.be/2gUquvADF3A

Andy, N9VT, in northern Virginia provided this video for reception, same day time, and frequency. Andy’s location tends to be in the skip zone for 15670 kHz, i.e. its too close to the North Carolina transmitter for good shortwave reception, but his signal was S5, providing fair reception and decode:

http://youtu.be/DpOR0qe55XU

Gary, N3CZ, in Maryland, about 100 km, had good reception from the same 15670 kHz transmission thanks to his 8-element log periodic antenna:

http://youtu.be/YPJMuQ39a10

Have your lab coats ready, because VOA Radiogram for the weekend of 30 November and 1 December will full of experiments.

The first experiment has to do with last weekend’s slanted MFSK images. On Saturday, all listeners experienced badly slanted MFSK images. Merkouris, SV2HWM, in Greece quickly offered a solution by adjusting the sound card offset in Fldigi. I emailed this information to the group. Based on your responses, we agreed that a correction of -2250 ppm (parts per million), give or take depending on your sound card, produced the best results.

I still don’t know what caused the slant, but if a correction of -2250 ppm was necessary, this indicates that something on the VOA side was 0.225% too fast. This discrepancy in speed did not affect the decoding of the text, only the MFSK images.

This weekend we will begin the program with an image of a single vertical blue line, transmitted three times for a total of 2 minutes, 15 seconds:

In Fldigi, open this box: Configure > Sound Card > Settings. Set the RX Corrections to 0 (zero) or to whatever setting you use normally. As the vertical line is transmitted, if it is not vertical, try a different ppm setting, then click Save. Repeat this process until you have a vertical line.   

If the calibration is as bad as it was last week, with the top of the line slanting to the right like the image below, you will need another correction of -2250 (minus 2250) ppm, more or less:

If the slant to the right is less severe, as below, a correction of -1000 ppm should work:

If the top of the line slants to the left, as below, try a correction of 1000 (positive 1000) ppm:

Audio Harmonics

Our second experiment involves the audio harmonics that many of you have noticed during VOA Radiogram broadcasts. They are sometimes noticeable on the Fldigi waterfall. For example, in the image below, the MFSK32 fundamental is from 1250 to 1750 Hz, with the bottom half of the second audio harmonic visible starting at 2500 Hz. It is actually from 2500 to 3500 Hz:

The transmitter in North Carolina is operating according to specifications, but there will always be some degree of audio harmonics. They are more noticeable with the digital text modes because the fundamental RF is very fixed between two frequencies, rather than diffused over a wide range as in voice transmissions.

The audio harmonics generally do not seem to impair the decoding of the text modes. For example, MFSK64 with our typical center frequency of 1500 Hz extends from 1000 to 2000 Hz, with the second harmonic safely out of the way from 2000 to 4000 Hz. Below is the MFSK64 as spectrally displayed on the University of Twente SDR receiver in the Netherlands. The fundamental in this double-sideband AM signal is 15668-15669 and 15671-15672 kHz, with second harmonics at 15666-15668 and 15672-15674 kHz:

Robert, KK5VD, in Alabama suggested this experiment: If we move the center frequency of MFSK64 to 1000 Hz, the fundamental will extend from 500 to 1500 Hz. The second harmonic will be from 1000 to 3000 Hz, so there will be an overlap. Will this have a negative effect on the decoding of the MFSK64?  We will investigate this question by transmitting the same VOA News story in MFSK64 centered on 1500 Hz, followed by the same story in MFSK64 centered on 1000 Hz.  We will repeat the experiment using the new long-interleave mode MFSK64L.

Here is the lineup for VOA Radiogram, program 35, 30 November/1 December 2013:

  1:37  MFSK16: Program preview (3:01)
  4:43  MFSK32: Slant test with 4 images (5:18)
10:03  MFSK32: Introduction to audio harmonic experiments (2:32)
12:33  MFSK64 1500Hz/1000Hz: Philippines radio (3:56)
16:27  MFSK64 1000Hz: W7VOA image (1:55)
18:24  MFSK32: Email address and intro to MFSK64L tests (:44)
19:08  MFSK64L 1500Hz/1000Hz: Ivanpah solar power station (5:30)
24:39  MFSK32: Image of Ivanpah facility (2:37)
27:13  MFSK32: Closing announcements (:32)
27:46  MFSK32: VOA Radiogram logo (:36)

Please send reception reports to radiogram@voanews.com

VOA Radiogram transmission schedule
(all days and times UTC)
Sat 1600-1630 17860 kHz
Sun 0230-0300 5745 kHz
Sun 1300-1330 6095 kHz
Sun 1930-2000 15670 kHz
All via the Edward R. Murrow transmitting station in North Carolina.

Tim, K0RUS, in Colorado produced this YouTube video of his reception and decoding of VOA Radiogram, 23 November 2013, 1600-1630 UTC. The MFSK images in his video show the slant that was a problem during the weekend. You can decode the broadcast using the audio from this video, with unslanted images if you make this adjustment in Fldigi: Configure > Sound Card > Settings > under Corrections, set RX ppm to -2250.  

http://youtu.be/7IRQgOCJ8r8

Tim produced another YouTube video from his reception 24 November 2013, 1930-2000 UTC, on 15670 kHz. This time the MFSK images are unslanted because he made the RX ppm correction before the broadcast:

http://youtu.be/iEbLAkgs3rU

Marco, IK0DWN, in Italy provided this video of his reception, same time, same frequency, also with the -2250 ppm RX correction:

http://youtu.be/Kh533TyRP1U

Gary, NC3Z, in Maryland produced this YouTube video of his reception 24 November 2013, 1300-1330 UTC, on 6095 kHz. Typically the signal strength on 6095 kHz from the North Carolina transmitter is very big in the US mid-Atlantic region. The RX ppm adjustment was not made, so the images are slanted. You can decode unslanted as described above:

http://youtu.be/gSI5g1wim7w

After the first airplay of VOA Radiogram program 34, 23 November 2013 at 1600-1630 UTC on 17860, listeners sent in badly slanted MFSK images. Obviously there was a problem on the VOA side.

Merkouris Gogos sent unslanted images because he adjusted the Fldigi sound card setting. Based on Merkouris’s information, I sent an email to the group, and most of us used an audio adjustment of -2250 ppm (parts per million) to achieve unslanted images. This indicates that something on the VOA side was 0.225% too fast.

Mark Hirst in the UK decoded the image on the left live from the recording, then decoded the same image on the right from his recording after setting the Fldigi RX correction to -2250 ppm:

Michel Morisse in France did the same:

Bob Nerozzi in Italy added an adjustment of the pitch to clean up as well as unslant the images. I’m not sure how or why this works, but it obviously does work:

During the weekend of 23-24 November 2013, VOA Radiogram listeners have been receiving badly slanted MFSK images. The problem is somewhere at the transmission end.

This weekend, to receive unslanted images, use this Fldigi setting:
Configure > Sound Card > Settings > Corrections > RX ppm set to -2250

You might have to adjust that RX ppm a bit for your PC and sound card.

If you want to decode from the “studio” recording of this weekend’s broadcast:

soundcloud.com/voaradiogram/voar34

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

Remaining broadcasts today, Sunday, 24 November:

1300-1330 UTC on 6095 kHz

1930-2000 UTC on 15670 kHz