Tektronix 1705A Looking at Exciters with the 70 MHz Input

Introduction
1-16 1705A Spectrum Monitor
Tek
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--20
--30
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--70
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Figure1 -8: Simulationof a1705A FULL SPAN/DIV display showing six transponders
illuminated
The 70 MHz Input to the spectrum monitor is a bnc connector. It is designed for
use with the IF signal froman up link exciter. Most up link transmitters use an
exciterto drive an Upconverter and High Power Amplifier (HPA), and, in most
cases, the driving signal to the Upconverteris a 70 MHz IF. If the exciter output
is at the up link frequency,a 70 MHz monitoring point is often provided.
Sometimes the coupling of the IF signal between the exciterand Upconverter is a
coaxial link thatcan be opened and a directional coupler installed for sampling
purposes. See Figure 1-9.
NOTE. The 70 MHz input is rated at --20 dBm maximum, external pads may be
requiredto meet this operating condition.
Once a directionalcoupler is installed a whole series of checks can be made,
including presenceof the proper carriers and an indication of the modulation
level. More detail can be found in theTektronix Television booklet “Television
Operational Measurements; Video and RF for NTSC S ystems.”
Looking at Exciters with
the 70 MHz Input