Hello friends,The MFSK16 mode performs well in difficult reception conditions, but it is slow (55 word per minute).This weekend, we will experiment with the simultaneous transmission of two MFSK16 signals, one on a center frequency of 700 Hz, the other on 2000 Hz. By transmitting the first half of a news story on the left "channel," and the second half on the right, the speed of MFSK16 is effectively doubled.The additional speed does come at a price. The transmit power is now divided between the two MFSK16 streams, resulting in a lower signal-to-noise (SNR) ratio for each.Reception of the two simultaneous transmissions can be accomplished by decoding sequentially from your recording. Or you can run two instances of Fldigi. On one instance of Fldigi, turn the RxID on. On the other, turn the RxID off. The RSID will be transmitted for the 700 Hz MFSK16 transmission and will (we hope) guide your first instance of Fldigi to the correct audio frequency. It will not be transmitted on the 2000 Hz transmission, so use the 20-second tone to tune your second instance of Fldigi to the exact frequency near 2000 Hz. Decoding software must be tuned precisely for successful printout of MFSK16 text.Maybe all these steps are not worth the effort, but let's see what happens.Here is the lineup for VOA Radiogram 43, 25-26 January 2014 (all modes centered on 1500 Hz except where indicated):1:38 MFSK32: Program preview3:52 MFSK16: IMF 2014 world economic outlook9:32 MFSK16 at 700 and 2000 Hz: Same VOA News story13:22 MSFK64/Flmsg: Global effects of net neutrality debate,with image20:09 MFSK64: China Internet outage, with image23:52 MFSK64: Image of Kim shoveling snow25:42 MFSK32: Closing announcementsPlease send reception reports to firstname.lastname@example.org.With VOA Radiogram 43 now produced, I will continue to respond to your reception reports.KimKim Andrew ElliottProducer and PresenterVOA Radiogramradiogram@voanews.comTwitter: @voaradiogramVOA Radiogram transmission schedule
(all days and times UTC)
Sat 0930-1000 5745 kHz
Sat 1600-1630 17860 kHz
Sun 0230-0300 5745 kHz
Sun 1930-2000 15670 kHz
All via the Edward R. Murrow transmitting station in North Carolina
Thursday, January 23, 2014
Really Interesting VOA Radiogram for January 25-26
This weekend, VOA Radiogram is doing an interesting (if geeky) experiment with MFSK16. This proposes a doubling of this mode's speed by transmitting two signals simultaneously. They will be centered on 700 and 2000 Hz. These will each carry half of a VOA news story. The listener should either run two instances of their decoder program (usually Fldigi), or make two passes from a recorded transmission.
I've had interesting results with sequential decoding of MFSK images. Fading often affects the two sidebands independently, and often a line of noise in one is a reasonable decode of that line in the other. In this case, however, the user must capture the images sequentially in USB and LSB, and assemble the finished composite with an editing program like Photoshop. It's tricky, and some skill is required.
I've wondered, though, whether software could analyze lines of pixels and pick the best ones of the two, then write out the composite image.
Anyway, this is from Kim Andrew Elliott:
Posted by BlogAdmin at 13:52