HP 8340A Service Manual page 54

Type C3, crossing frequency when:
Fmn/Flm 20*I
=
or
.Flf 20 * K * (20-M/N)/20*I
=
ORDER of spur
This type is caused by the Ith harmonic of the PLLl VCO sampled by the Kth harmonic of
the M/N VCO.
For any CW frequency, selecting the appropriate SHIFT functions will display the M/N
frequency, 20/30 frequency and YO frequency. A synthesized spurious response must be a
function of these signals. As mentioned above, the elimination of these spurs is primarily a
design considseration; however, any coupling from one signal path into another may result
in a spurious response (i.e., loose connectors, poor shielding, cable routing, etc.).
Band 0 spurs are caused by mixing products in the Band 0 mixer. These are not crossing
spurs because they are not YO Loop sidebands. Instead, they are added to the output as part
of the down-conversion process. The YO output should mix with the 3. 7 GHz oscillator
output and produce a single mixer output at Fyo - 3.7 GHz. However, harmonics of both
oscillators are present, or are generated in the mixer. These mix to form spurs on the output.
Troubleshooting synthesized spurs - One way to eliminate various RF paths is to determine
the YO frequency at which the spur occurs, then select a CW frequency in both Band 0 and
Band 1 that uses the YO frequency. If the spur occurs only in Band 0, troubleshoot the Band 0
RF path. If the spur occurs in Band 1, troubleshoot the Band 1-4 RF path.
Change the CW frequency such that the M/N output remains constant and only the 20/30
output changes. Determine the order of the spur (i.e., Ratio of YO frequency change to spur
frequency change). If the spur is a crossing spur at some point the spur will be on top of the
YO frequency and at some point (50 kHz away from the YO frequency) the spur amplitude
will decrease. If the spur is a crossing spur, refer to the appropriate spur family type above.
It may help determine which internal frequency source(s) is generating the spur by:
Change the CW frequency while monitoring the SHIFT function diagnostics, looking for
a sudden change in spur frequency and/or amplitude. For example, press
then change the CW frequency. Look for a correlation between any sudden change in spur
frequency and/or amplitude with a change in M/N output frequency or 20/30 output
frequency. If a sudden change in the spur occurs at the same time the M/N or 20/30 makes
a large change, the internal frequency source that changed is probably one of the signals
that is generating the spur.
If the 20/30 loop is suspected, press
PLL3 Up Converter frequency and repeat the above test.
For more information on the diagnostic modes, refer to the Fre­
quency Range and CW Mode Accuracy test in Section IV.
19. 1/0 CONNECTORS
To determine source or destination of input or output connector signals, refer to the Front
and rear panel section wiring diagrams. For troubleshooting, refer to the source or destina­
tion assembly Theory of Operation and Troubleshooting.
20.
REMOTE OPERATION
Section IV contains an HP 8340A HP-IB Operation Verifi c ation Programming Listing. This
program will verify the ability of the HP 8340A to respond to a remote input (complete HP­
IB handshake).
Model 8340A - Service
J /(2*K)
±
J
±
20*I J /(2*K)
±
=
[SHIFT] [M3]
NOTE
Scans by HB9HCA and HB9FSX
to display the PLL2 VCO frequency and
[SHIFT] [M1]
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