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RECEIVER DESCRIPTION'
RF signals present at the antenna connector on the rear panel are switched
to the double tuned low-noise GaAsFET preamplifier. The preamplifier has been
optimized for gain, thermal noise and image rejection. As a result, the receiver
conversion noise figure is better than 1.5 dB in the 430 MHz band.
The RF signal is then down-converted
to a channel 3 or 4 IF by mixing with a
user-selectable
LO. RX TUNE on the front panel may be used to manually tune in
a station which has drifted to the extent that reception with one of the crystal oscil-
lators is compromised. The desired IF sideband is filtered to remove the LO and
image sideband then presented to the TV output connector on the back panel.
The signal at the TV connector may be viewed on channel 3 or 4 of any standard
US television set.
OUTPUT POWER LEVEL ADJUSTMENT
I
Warning!
WarninQI]
Adjust only C104, L13, L14, R39, and R98 per the Instructions in this manual.
Any other adjustments should be made only by a qualified technician using a
spectrum analyzer, tracking generator, synthesizer, frequency generator, dummy
load and wattmeter. Currently, a $50.00 charge will apply to all units which are
returned to AEA for re-tuning ...
Your VSB-70 has been delivered with the output power preset to one watt
I
PEP on sync peaks into a 50 ohm load. There are occasions when it is neces- .
sary to adjust the output power to a different level (such as interfacing with an ex-
ternal power amplifier). The output power level may be adjusted by rotating C104
(see Figure 4) while a black level signal is input to the unit.
The procedure for adjusting the output power level is as follows:
1. Follow the instructions for TRANSMIT MODE OPERATION
using a video
camera or Camcorder for the signal sourc;e (i.e. turn on the unit and optimize
the picture quality) .
. 2.
Cover the lens of your video camera or Camcorder with a black lens cap. This
provides the black level input signal to the unit.
Adjust C1 04 (see page 12) with the non-metallic tuning tool until the power is
at the desired level. A power meter must be used to determine the absolute
power level. If you have a high-quality PEP power meter, then adju$t the power
level directly from the indicated output reading. If you have a Bird (or equivalent)
power meter, then scale the desired level relative to 0.6 watts. For example, a
Bird power meter will read 0.3 watts for a 0.5 watt PEP (0.6 x 0.5) output power
level.
IWarning!
Warning! I
The variable
capacitors
are not designed
to be repeatedly
adjusted
-
they can become unstable
and loos~. Do not repeatedly
tune these
capacitors!
10
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