[aprssig] APRN news from Dayton!

Stephen H. Smith wa8lmf2 at aol.com
Thu May 26 20:37:31 EDT 2011

On 5/26/2011 3:29 PM, Scott Miller wrote:
>> Consider the "narrowband" MP73-N format as well. There is an increasing
>> amount of interest in this mode on 30 meters. Its occupied bandwidth of
>> only 500 Hz makes it the only legal format for SSTV (in the US at least)
>> on this non-voice band. There is now even a Yahoo! group dedicated to
>> 30meterSSTV activity.
> Any idea where I could find the detailed technical specs? That's usually the 
> hardest part of implementing new modes. Lots of chatter out there, and people 
> who think they know what they're talking about, but not much solid information.
> Scott
> N1VG
> __

There is a text file in the main mmSSTV directory, "modes.txt" that contains 
notes on the MP and ML modes including the MPnn-N narrow modes. The contents of 
this file are quoted below.

New SSTV modes added in MMSSTV

Written by JE3HHT Makoto Mori
Translated into English by JA7UDE Nob Oba

1. VIS code

All the even-parity codes in the VIS have already been used now. If I use the 
remaining odd-parity codes for defining new modes, it is a matter of time to 
run out of them. For this reason, I have extended the VIS code to 16 bits as 

1900 300ms
1200 10ms
1900 300ms
1200 30ms
d0 30ms
d1 30ms
: :
d15 30ms
1200 30ms

(d0-d15 : 1-1100Hz, 0-1300Hz)

When you assign a code to your new mode, it is a good idea to use an odd parity 
code, which is not in use now, in the least 8 bits (d0-d7), so as not to get 
the conventional 8-bit VIS decoder confused. For this reason, MMSSTV uses VIS 
code 23H in d0-d7. If you add a code for your new mode, I would recommend you 
to assign some code other than 23H in d0-d7, so that you can make full use of 
upper 8 bits to represent up to 256 modes.

2. MP mode

MP mode is based on the color difference scheme used in PD mode. I have added 
this mode for alleviating multi-path/jitter effects on the 20-meter band. To 
increase the scan time for each pixel, the color information is compressed 
along the vertical axis.

Mode Size VIS TW [ms]
MP73 320x256 2523h 140.000
MP115 320x256 2923h 223.000
MP140 320x256 2a23h 270.000
MP175 320x256 2c23h 340.000

1200Hz 9.000ms
1500Hz 1.000ms
Y(odd) TW
Y(even) TW
(Repeat 128 scans)

3. MR/ML mode

MR/ML mode is based on the color difference scheme used in Robot 24/72 mode. It 
is aimed to provide good resolution under good condx. The color information is 
compressed along the horizontal axis.

Mode Size VIS TW [ms]
MR73 320x256 4523h 138.000
MR90 320x256 4623h 171.000
MR115 320x256 4923h 220.000
MR140 320x256 4a23h 269.000
MR175 320x256 4c23h 337.000
ML180 640x496 8523h 176.500
ML240 640x496 8623h 236.500
ML280 640x496 8923h 277.500
ML320 640x496 8a23h 317.500

1200Hz 9.000ms
1500Hz 1.000ms
LP 0.100ms
R-Y TW/2
LP 0.100ms
B-Y TW/2
LP 0.100ms
(Repeat 256 or 496 scans)

LP = output the last pixel signal

4.MP-N mode
@This is a narrow band version of the MP mode. The scan signals occupy 2044Hz 
to 2300Hz.

Mode Size N-VIS TW[ms]
MP73-N 320x256 02h 140.000
MP110-N 320x256 04h 212.000
MP140-N 320x256 05h 270.000

1900Hz 9.000ms
2044Hz 1.000ms
Y(odd) TW
Y(even) TW
(Repeat 128 scans)

5.MC-N mode
This is a narrow bande version of the RGB mode. The scan signals occupy 2044Hz 
to 2300Hz.

Mode Size N-VIS TW[ms]
MC110-N 320x256 14h 143.000
MC140-N 320x256 15h 180.000
MC180-N 320x256 16h 232.000

1900Hz 8.000ms
2044Hz 0.500ms
(Repeat 256 scans)

7.N-VIS mode
The VIS code of the narrow band modes are defined by the 24-bit FSK as follows. 
One symbol consists of 6 bits.

1900Hz 300ms
2100Hz 100ms
1900Hz 22ms start bit
D05 22ms (1=1900Hz, 0=2100Hz)
D04 22ms :
D03 22ms :
D02 22ms
D01 22ms
D00 22ms
D15 22ms
D14 22ms
D13 22ms
D12 22ms
D11 22ms
D10 22ms
D25 22ms
D24 22ms
D23 22ms
D22 22ms
D21 22ms
D20 22ms
D35 22ms
D34 22ms
D33 22ms
D32 22ms
D31 22ms
D30 22ms

D0(D05-D00) = 101101
D1(D15-D10) = 010101
D2(D25-D20) = N-VIS
D3(D35-D30) = 010101 .xor. N-VIS

e.g. MP73-N = 101101 010101 000010 010111

It is free to use these modes in any kind of software or equipment. You do not 
have to inform me. Feel free to do it.

73 Mako



Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: WA8LMF or 14400 [Think bottom of the 2M band]
Skype: WA8LMF
Home Page: http://wa8lmf.net

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