[HATS] Narrow Band TV Programs (New FM Version)

[Les Rayburn]

Over the last few weeks, I have received numerous e-mails and requests for 
information
about Narrow Band Television (NBTV). Recently, a lot of that interest has come
from both the SSTV and ATV camps. Many are interested in conducting on-air
tests of the mode. I am suggesting the following:

A brief hour long net on 14.233khz on Saturday mornings at 0900EST. This 
frequency
is used has a secondary calling frequency for the SSTV crowd, and I think that
our transmissions will generate a lot of interest there.

For at least the next two weeks, I may participate only with SSB audio and
reception tests. I am awaiting a repair to my "Rigblaster" module, and 
currently
cannot transmit either SSTV or NBTV. However, reception is not a problem.

I suggest that we use standard SSTV operating practices. Calling the net and/or
CQ first on SSB before transmitting any images in NBTV. We should also
be sure to transmit the web sites where the NBTV programs can
be downloaded.

If you plan to participate, please respond to the lists and let us know. Below
you'll find links to the latest FM version of the software developed by
Con, ZL2AFP and his latest notes about it's operation. Let's try
some NBTV this weekend!

73,

Les Rayburn, N1LF
-----------------------------------------------------------







As promised Con has worked out a first edition of his NBTV software that 
uses FM rather
than AM modulation. I have not yet had a chance to test these on the air, 
but I expect
that most of us will see some improvement.

You can download the software from the links below:

http://www.highnoonfilm.com/tvdx/Rxfmtv.exe
http://www.highnoonfilm.com/tvdx/Txfmtv.exe

As usual, the text of Con's notes are included below. Please keep the list(s)
advised of any on air experiments that you conduct. We'd love to get some
testing going on 20 meters so that more folks can monitor them...

-----------------------------------------------------------------

Les


As promised, here is my first attempt at an FM subcarrier version of my TV
programs. I have used fairly simple frequency modulation and demodulation
techniques. The modulation uses the phase accumulation method (sounds
complicated but is actually a piece of cake to implement, only about 2 lines
of code) and the demodulation uses I and Q channels, a lot of filtering, and
a simplified method for taking the differential of arc tangent of Q/I (the
basic method is in the ARRL Handbook). Again, only a few lines of code
(except for the filtering!).


Because of all of the simplifications, it is probably not quite as good as
the SSTV programs that are out there. MMSSTV is probably the best one in my
opinion, and it is likely that these techniques are used also, but I have
not seen the source code so I can only speculate.


To get the best picture, the video capture card settings should be set so
that there is not too much contrast, otherwise the white areas of the
picture tend to show what appear to be phase shifts at the edges. This may
be due to the way I have tried to squeeze as much signal as possible into
the limited bandwidth available, and I may be skating too close to the upper
limit.


The 800, 1000, 1200Hz low pass filters may be useful to get some more detail
from the picture, but at the expense of some carrier leaking into the
picture. This is a matter for experimentation.


The picture is tuned in the same as SSTV. If the signal is too high in
frequency, the picture will be too bright, same as SSTV.


If the signal input level is too low, the picture will be noisy; too high
and the carrier leaks into the picture. It is not too critical though. It
should be a lot easier to use than my AM versions (I hope!)


Unlike SSTV, which works with USB, this program uses LSB. It should work on
USB, but the picture will be a negative.


Please let me have any feedback so that I can improve the programs. I have
used 36 lines, as this gives me equal resolution in both vertical and
horizontal directions. It enables a frame speed of 2.8fps.I would be
interested to know if folk would prefer more resolution (and a lower frame
rate), or lower resolution and a higher frame rate. I find that 2-3fps is
quite easy to get used to, as it is not quite "real" ATV but not the very
slow SSTV either. It is sort of somewhere in the middle, a bit like Internet
video gone wrong!


Good luck and 73
Con ZL2AFP



Les Rayburn, N1LF
4919 Cox Cove
Helena, AL 35080
XMGR 184.8988khz WOLF Mode
1LF 187.300khz

Looking for a challenge? Try the ultimate weak signal mode, on 1750 Meters!
Visit the Noise Floor!
http://www.highnoonfilm.com/xmgr




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