PC Electronics TX70-5 70, TX70-5 User Manual

P. C. Electronics 2522 Paxson Lane Arcadia CA 91007-8537 USA ©2009

Tel: [phone] m-th 8am-5:30pm pst (UTC - 8) Tom (W6ORG) & Mary Ann (WB6YSS)

Web site: http://www.hamtv.com Email: ATVinfo @ hamtv.com

TX70-5 70 CM ATV TRANSMITTER

USERS MANUAL

The TX70-5 transmitter is designed to provide over 0-5 Watt continuous duty peak envelope
power (sync tip) of video modulated RF in the 70 CM (420-450 MHz) amateur band. Any licensed
Technician class or higher Radio Amateur may operate this transmitter in accordance with 47 CFR part
97 of the FCC Rules and Regulations. The TX70-5 accepts U.S.A. standard composite video (1 volt pk­pk) from any source such as color or black and white TV cameras or camcorders, VCRs, or computers
for transmission. Audio from these sources or a low impedance dynamic mic is also transmitted on the

4.5 MHz sound subcarrier. Transmit / receive power and antenna switching is provided for the compan­ion TVC-4S downconverter.

PLEASE read through this manual before plugging in an cables and attempting operation. Each
connector and control is described here to enable your proper hookup and operation. Also the unique
video practices associated with ATV and the 70 CM band are described.

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W6ORG ©2009

REAR PANEL:

POWER INPUT JACK. A 4 pin plug and 3 ft long #18 cable

is provided for connection to your source of +12 to14 Vdc.
Currant draw is 500 MA in transmit. Pin 1 is ground (black)
and pin 2 (red) is +. The TX70-5 works best from a well
regulated voltage source with leads no longer than necessary.
The transmitter is set up by us from a regulated 13.8 Vdc
supply. Do not exceed 15 Vdc input. There is a 16 v zener
which should blow the fuse if this voltage is exceeded or the
supply leads get cross connected, but semiconductors have
been known to protect fuses. If a new fuse immediately blows
again, check and replace the 1N4745B 16V zener located
near the fuse holder inside.
Any ripple or noise on the DC line may be seen in the
transmitted video. For this reason, if a single large power
supply is used to power this and other equipment, all leads
must connect directly at the power supply terminals, not to
an external terminal block. If a 50 or 70 watt amp is added,
it is best to run it from its own separate power supply. A
Radio Shack 13.8 Vdc 3A regulated power supply will run
both the TX70-5 and TVC-4S.
Pin 4 has the applied + voltage when the T/R switch is in
the receive position in order to power an ATV downconverter
such as the TVC-4S. Pin 3 is ground. If a TVC-4S is used,
the wall plug supply may be disconnected and a two wire
cable made up to run from pins 3 and 4 to the 2.1mm jack.
Take care to insure that the tip of the power plug is connected
to the positive voltage on pin 4 of the TX70-5 power input
jack, and that there are no adjacent pin shorts in the 4 pin
plug with an ohm-meter before reinserting into the TX70-5.

1 AMP FUSE INSIDE. The TX70-5 itself draws about 1.5
amp in transmit, and .1 amp plus external downconverter in
receive - a 2 or 3 amp 3AG fuse should handle both.

TO MONITOR. This output provides camera video during
receive periods to enable you to best adjust focus and
lighting, etc., rather than a distant station describing these
back to you on 2 meters. Use a RCA plug shielded cable to
connect to your video monitor or VCR video in. If you do not
have a video monitor, the Radio Shack 15-1273 RF Modulator
can take the composite video and modulate it up to channel
3 or 4 to make a second TV set into a monitor. Attempting to
monitor off the air with another TV set at the same QTH most
often gives false indications due to overload and reflections.
Even receiving the 2nd harmonic 40 or more dB down around
channel 80, or on cable channels between 57 and 60 can
give an erroneous indication of transmitted picture quality.

50 OHM 70 CM ANTENNA. A UG21 type N plug is pro­vided to attatch to low loss .5" size 50Ω coax. Losses at 70
CM are very high in transmission lines. We suggest using
the foam filled types (3.5 dB/100') such as Belden 8214, or
semi rigid (2.5 dB/100') Belden 9913. Put the connector
together properly. See ARRL HandBook Chapter 37. The
type N connector has good moisture resistance and low loss
at UHF but use two layers of vinyl tape or coax seal on all
outside connections to prevent moisture contamination. The
antenna and feed line are the most important part of your
ATV system, and therefore the last item to just try and get by
with.
Take great care with preparing connectors and cable. On
initial turn on, do not transmit more than 10 seconds if the
reflected power is more than 10% or 2:1 VSWR. You could
damage the VM-70X module. Also, VSWR or being too near
your antenna can cause RF interference in your camera or
buzz in the audio. With no video connected, the RF power
meter should read between 4 to 5 Watts sync tip, p.e.p.,
power.
Use a good resonant broad bandwidth 70 CM antenna.
Do not be tempted to just try it out with a rubber duckie, 2
meter antenna, or other antenna not specifically designed
for the video carrier frequency. Place the antenna as high
as practical, at least above the trees or roof tops. See the
section on dx vs. power vs. gain on page 4.

TO DOWNCONVERTER. This BNC output jack is connected
to the antenna input of your 70 CM 420-450 MHz ATV down­converter. Downconverters for other bands are not connected
to the TX70-5, rather to their own antenna and left on when
transmitting on 70cm for full duplex or crossband repeat. If
a TVC-4S downconverter is used you will need a short 50
Ohm cable with a male BNC on one end and type N on the
other. This can be made up with Radio Shack RG58/U (276-

1326) plus UG88 (278-103) and N (278-151) connectors or
equivalent. Keep this lead short to minimize losses in receive.
The TX70-5 contains a T/R relay to switch the antenna input
between the downconverter and the transmitter. See the
Power Input Jack paragraphs two and three for power
connections.

FRONT PANEL:

VIDEO INPUT. This input accepts any standard NTSC

composite video into 75Ω from cameras, VCRs, computers,
SSTV or RTTY converters, home satellite converters, etc.
Use RCA phono plug and shielded cable (Radio Shack 15-

1535) up to 12' or RG59 for longer runs.

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