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LINE AUDIO INPUT. High level line audio usually from the
same source as plugged into the companion Video input is
plugged into this jack using another RCA phono plug shielded
cable. Minimum level is .1 v pk-pk into a 10K load. The level
is controlled by the line audio gain knob.
LINE AUDIO GAIN control varies the high level audio applied
to the subcarrier from the front panel audio input RCA phono
jack. Increas ethe level to the point where the red XMIT light
winks off, and then back down the gain slightly. This audio is
independent from the mic audio and is mixed in the subcarrier
generator. This makes varying the level of a video tape audio
verses mic for voice over comments easy.
MIC jack accepts any low Z dynamic mic in the range of 100
- 600 Ohms with a mini plug. Mic audio is active at all times
and mixes with the camera or VCR line audio input to more
direct pickup, commenting while running video tapes, etc.
Mikes must have a shielded cable to prevent RF pickup hum
and buzz. Unidirectional mics are suggested for full duplex
to minimize speaker feedback or to reduce pickup of
unwanted sounds and noise. Electret and amplified mics
are very susceptible to RF pickup - buzz and should not be
used.
MIC GAIN control varies the level of the low Z microphone.
It is independent of the line audio level. Speak directly into
the microphone at the normal operating distance. Increase
the level to the point where the red XMIT light winks off, and
then back down the gain slightly. There is a volume
compressor that will keep the audio at the standard 25 kHz
deviation and 40 kHz peaks. Audio usually drops out about
the same time as color does in a snowy picture - P3 -
depending on the TV sets audio IF gain and limiting.
CHANNEL SWITCH. This model has 5 synthesized
channels:
1 - Open - *can be special programmed
2 - 426.25 MHz also is the open switch default.
3 - 427.25 MHz
4 - 434.00 MHz
5 - 439.25 MHz
*421.25 MHz can only be used with a VSB filter in the
antenna line to keep sideband energy from falling outside
the band edge at 420 MHz as is done at a repeater site.
439.25 MHz only can be used in Canada and those above
the A line - approx 100 miles south of Canada - in the USA
since the band edge is 430 MHz.
XMIT/REC switch. It is in parallel with the EXT KEY jack.
The red lamp above this switch will light whenever you are in
the transmit mode and the audio inputs are below 40 kHz
deviation. There can also a delay of up to 1 second for this
LED to light eventhough there is RF output. In receive, the
applied + voltage appears on the downconverter power jack
to power a TVC-4s 70CM ATV downconverter.
POWER ON switch turns on the applied +12 to 14 Vdc to the
TX70-.1s. If the green light does not come on, check the
internal fuse and why it blew before replacement.
OPERATING NOTES: ATV practices are somewhat different
from the other bands and modes. 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. This is why 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).
Two meters, even for FM, has about 9 dB less path loss
than 70CM 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
70CM 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 70CM 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,
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 900 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 TX70-.1s is
portable enough to give a little demo at your local radio club
or hamFest.
IF YOU BELIEVE THE TX70-.1s ISN'T WORKING,
check all cables and connections, internal fuse and 16V
protection zener, VSWR, power supply and DC voltages
at the board test points. 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 TX70-.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.
Return Authorization Form - download from our web
site. It will be sent back normally within 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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