[A-DX] VOA Radiogram slow modes to Australia

[Roger]

ok, once again with the correct system date and time........



> Am 30.01.2016 um 12:39 schrieb  [dxld]:
>>
>> Using Fldigi <http://w1hkj.com> or TIVAR 
>> <http://sourceforge.net/projects/fldigi/files/AndFlmsg/TIVAR/>, try 
>> decoding this audio of VOA Radiogram <http://voaradiogram.net> Olivia 
>> 64-2000 (25 wpm) and MFSK8 (30 wpm) by a receiver in Sydney, 
>> Australia, 15000 km from the North Carolina transmitter ...
>>
>> https://t.co/2ike5zvB7Z
>>
>> Given the reception conditions, voice would probably be 
>> unintelligible, and the faster MFSK32 generally failed.
>>
>> Kim
>>
>
> http://voaradiogram.net/post/138335362002/voa-radiogram-as-received-in-sydney-nsw
>
> "....VOA Radiogram as received in Sydney, NSW, Australia, 30 January 
> 2015, 0948 UTC, 5865 kHz, via North Carolina transmitter. Modes are 
> Olivia 64-2000 and MFSK8, each preceded by a 15-second tuning signal 
> transmitted at 1500 Hz but received at 1384 and 1612 Hz (1612 seems to 
> decode more successfully). Transmitter was AM, but receiver was set to 
> USB. Some unsuccessful MFSK32 is included at the end of the 
> recording....."
>
>
> Decoding could be better, but in the audio is a big mistake !!
>
> In the audio, there are two signal-centers: at 1500 +/- 100 Hz.
> That means:  both Olivia, as well as in MFSK there are two center 
> frequencies:  about 1390 Hz + 1610 Hz.
>
> This clearly means:
> 1.  reception was on 5865,110 kHz (110 Hz higher)  or  110 Hz deeper
> 2.  decoding was NOT only in USB, but USB + LSB = DSB,  without S-AM
> 3   because of that: both NF spectra do not overlap congruently !!
>
>
> Thereby:    AF demodulation was NOT correct !!!    roger


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"...Given the reception conditions, voice would probably be 
unintelligible, and the faster MFSK32 generally failed. "

I disagree.
With proper demodulation MFSK-32 (16-FSK !!) is better than MFSK-8 
(32-FSK !!)
I have checked this with an audio recording of Mark Hirst (2E0ECN), also 
from a weak 5865 kHz.
The s/n  of MFSK-32 was always 4-5 db better than that of MFSK-8 kHz, 
here there were also errors.


But why was MFSK8 better than MFSK32 in the "incorrect" Australia-audio 
recording ??
MFSK8 has a narrower bandwidth.
When there is an invalid DSB-demodulation with 110 Hz frequency shift, 
there are fewer false overlap.
MFSK-32 is broader - there is a much greater destructive overlap during 
false demodulation - this is the explanation.
In the even broader Olivia-64-2000, the tones are more concisely placed.
The method for error protection is still much more effective.

The filligrane MFSK8 with its 32 *narrow* tones can never be as robust 
as an MFSK-32 with its 16 wider tones - that's my opinion.

http://www.rhci-online.net/radiogram/VoA_Radiogram_2016-01-30.htm#mfsk




roger