OFDM NBTV Update 2020
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OFDM:	Orthogonal Frequency Division Multiplex
NBTV:	Narrow Band Television

This suite of programs was originally developed in 2007, and intended to operate on Windows 95
or Windows 98. It has since been found to work on Windows XP. However, there are issues when
using the software with Windows 7 and Windows 10, hence this update.

OFDM NBTV is an analogue technique. The transmission technique used is quite different from
conventional TV - each line is transmitted separately, but all lines are sent at the same time,
on a slightly different frequency. Because the transmitter and receiver operate at precisely
the same speed, controlled by the computer sound card, there is no need for any sync pulses
to align the picture; in fact there is no automatic synchronizing mechanism at all - it simply
isn't necessary.

Modulation on each of the many carriers is very narrow FM (a few Hz), for best noise rejection,
and the overall transmission bandwidth is only 2kHz, so an SSB transmitter and receiver can be
used. The transmit and receive software will operate at the same time, so you can receive your
own or another station while transmitting, perhaps using a full-duplex link or KiwiSDR.

While it is not possible to send moving pictures in real time, due to bandwidth limitations,
it is quite practical to send small movies slowly, record them, and subsequently play them at
full speed. The fastest OFDM NBTV mode sends one frame per second, 1/24 of movie speed.

Please read the web pages starting at https://www.qsl.net/zl1bpu/NBTV/OFDM.htm , which give the
background to the modes, how they work, and the differences between the versions.

Installation
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Simply unzip the supplied archive into a folder on your computer. C:\Radio\NBTV is suggested.

To operate the transmit programs, simply start the appropriate executable and select the
appropriate sound 'card', the one that modulates your transmitter. If the transmitter PTT is
controlled by a serial port, select that port from the Menu PTT item. If PTT control is not
possible in this way, for example using a CAT transceiver, you can operate the transmitter
using a third-party CAT program, such as FLRIG by Dave Freese W1HKJ.

To transmit using PTT, simply press the TX button. If you use CAT, press the TX button and
then the CAT controller PTT button.

To adjust the transmit output level, open the Sound Applet Volume Mixer, and adjust the
levels appropriately. The Menu Soundcard option only works with Win 95 and Win 98.

Otherwise follow the instructions at https://www.qsl.net/zl1bpu/NBTV/TX.htm . The programs
will transmit still pictures, moving GIFs, AVI and MPG movies (keep them short), and directly
from a webcam, digital camera, TV card, scanner or other TWAIN compliant device.

Still pictures, GIFs and movies can be dragged and dropped onto the picture window of the
appropriate tab. Keep the pictures simple - some good examples are given on the web page.

Reception
---------
While it is helpful to learn from the other station first what mode he intends to transmit,
you can fairly readily work out the mode from the cadence of the signal (1, 3, 6 or 9 second
frames). Tuning needs to be very precise, and you cannot use a VFO receiver: they simply are
not sufficiently stable. The tuning control and even the RIT control may also be too coarse
for effective tuning: use the Fine Tune control provided in the program.

Follow the instructions at https://www.qsl.net/zl1bpu/NBTV/RX.htm .
