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INTERNAL:
Also reference the wiring diagram on page 6.
AUDIO DEVIATION. Peak deviation is controlled by a pot
on the FMA5-G board for no more than 40kHz or 25 kHz
average. If you don't have a communication monitor tuned
to 4.5 MHz above the video carrier, you can come close by
comparing the sound level with a cable broadcast channel.
EXTERNAL LINEAR AMPLIFIER SET UP.
specific model amplifier application notes on our web site
and why some work on ATV and others do not. Basically,
they all setup in the same way.
1. With no video source plugged in, turn the RF power pot
on the TXA5 board to its minimum power position (CCW).
Turn the Pedestal pot to full CCW. No video pluged in. Make
sure the amp is rated to be linear class A, AB or B and is
connected to a good 50 Ohm dummy load or low vswr
antenna (less than 10% reflected).
2. Turn on the amp and transmitter. Slowly increase the
TXA5 board RF output to no more than 90% of the amplifiers
rated power output level. For instance if the amp is rated at
40 Watts, set the RF output for 36 Watts. This will be the
sync tip or peak envelope power. Then set the Pedestal pot
for 55% to 60% of this pep. In our example this would be
between 36 X .6 = 21.6 Watts and 36 X .55 = 19.8 Watts.
3. Plug the camera back in and have a distant station on two
meters talk back to check your picture to make sure you
have done the pedestal and sync tip set up correctly. There
should be no instability or rolling from sync compression. An
average reading RF power meter will read the pedestal power
when no video is plugged in. With video in, the avearage
reading meter will show less power even though the sync tip
and pedestal power will be constant. An all white picture will
show a little less than half pep.
OPERATING NOTES: ATV practices are somewhat different
from the other bands and modes. Another ham near you to
look for your video transmission will need to connect a 33cm
downconverter to a TV set on channel 3 and have a roof top
33cm antenna of the same polarity. Best if they talk back to
you on 2 meters. See our ATV Application Notes web page
for info on making a 33cm ground plane or simple beams if
they do not have one. Many ATV contacts are initiated by
calling or listening on an area 2 meter FM simplex ATV
coordination frequency (146.43 in 434.0 areas, and 144.34
in 439.25 transmit video areas due to the 3rd harmonic
relationship). Since we must use directional antennas to
make up for the 26 dB higher noise floor difference compared
to NBFM due to bandwidth (15 kHz vs. 3 MHz), the probability
of someone pointing their beam at you while at the same
time you at them and calling CQ is very low.
Two meters, even for FM, has about 12 dB less path loss
than 33CM so that all possible ATVers can be received on 2
meter FM using just an omni antenna. You will find with
experience the correlation between 2 meter simplex and
33CM ATV. It is much easier for all local ATVers to monitor a
squelched 2 meter FM simplex channel than to try tuning
and swinging the 33CM beam looking for sync bars. Once
another ATVer comes up on 2 meters, you can roughly swing
the beams on each other before turning on the ATV
transmitter. Then, if the picture is better than 20% snow, the
video transmitting station can talk on the sound subcarrier,
There are
and all those receiving him can talk back at the same time
on 2 meters (full duplex) to comment on picture content, etc.
Others listening to the 2 meter channel are often hooked
into ATV this way. You can also run full duplex audio and
video with another station on the 420 or 1200 MHz bands.
It is more fun as time goes on to have many hams put
their families, other hobbies, and varied interests on the
screen. Let others know your 2 meter ATV freq. by publishing
in local radio clubs newsletters, contact your local ARRL SCM,
or pick a night and time to start an ATV net. The TX33-.1s is
portable enough to give a little demo at your local radio club
or hamfest.
IF YOU BELIEVE THE TX33-.1s ISN'T WORKING, check
all cables and connections, internal fuse and 16V protection
zener, VSWR, power supply and DC voltages at the boards.
Then call or email us and describe the problem or ask any
questions you might have. It will save us both time and money
if we suggest some things to try that may have been over-
looked, or for us to better evaluate the problem. The TX33-
.1s can be repaired by us for $80 plus parts cost in a few
days if we believe the problem is customer caused or nothing
wrong. If we determine that it was due to our workmanship
and materials within a reasonable time and given
circumstances then your cost is only the shipping to us.
However the repair and service policy stated in our latest
catalog will supercede the general policy listed here. Include
with the unit a filled out Return Authorization Form - download
from our web site. Normal turn around is 2 days after we
receive it. There is no other warranty expressed or implied.
We believe this policy is more realistic than the usual 90 day
warranty other amateur manufacturers have since various
parts have different expected lifetimes.
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