General Operating; Information; Signal Application; Rf Input Connector - Tektronix 492 Operator's Handbook Manual

SECTION 3
GENERAL OPERATING INFORMATION
SIGNAL APPLICATION
Signal frequencies up to 21 GHz are applied through a
short, high quality , 50 2 coaxial cable , to the RF INPUT
connector. These signal pass through an internal RF
attenuator to the first ( 1st ) mixer . Option 1 version of the
492 has a filter selector that automatically selects either a
low- pass filter or tuned preselector (depending on fre
quency band) between RF attenuator and the 1st mixer.
Signals above 21 GHz are applied to an external
waveguide mixer . The output of the waveguide mixer is
then applied through the EXT MIXER port to the second
converter of the 492. Waveguide mixers and their applica
tion are described later.
RF INPUT CONNECTOR
The nominal input impedance of the coaxial RF INPUT
is 50 . Because cable losses can be significant at
microwave frequencies , it is important to keep the cables
as short as possible . Impedance mismatch between the
signal source and the RF INPUT will produce reflections
and degrade flatness , frequency response, sensitivity, and
increase spurious responses . Impedance mismatch can
be caused by poor connections , incorrect signal source
impedance, long or low quality coaxial cable , etc. When
optimum flatness or frequency response is desired and
signal strength is adequate , set the MIN RF ATTENuation
for 10 dB or more . The addition of the attenuator helps
minimize reflections to improve the input characteristics.
CAUTION
With MIN NOISE activated and 60 dB of MIN RF
ATTEN, the REF LEVEL can be set to +40 dBm . The
front end of the 492 is specified at +30 dBm
maximum . Do not increase input signal level to full
screen with a REF LEVEL of +40 dBm because this
will exceed the attenuator rating. DC input is limited
to zero ( ) volt.
492 Operator's Handbook
3-1