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Common Sweep Issues
Standing Waves
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Use a directional test point if available. Standing waves could still occur if a
mismatch is severe and close enough.
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Read from a tap. Some lower value taps may still give reflections depending
on port-to-port isolation and port-to-output isolation.
✓
Use a plug-in test point not a probe. Probes will always be bi-directional
unless they are in series with the circuit and a directional coupler is used.
✓
Install a terminating tap (4 port 8 or 8 port 11) if possible (make sure you
terminate the spigots). This is an easy way to isolate the system.
✓
Verify good test leads, connectors, F-81 barrels, etc. Use an in-line pad on
your test lead to determine whether the standing wave goes away. If it
disappears, a reflection is being created between the field unit and test point.
✓
Reverse: Keep all proceeding actives terminated for return sweeping. Do not
pre-stuff the reverse pad and EQ; noise funneling may hamper your ability to
sweep properly. A high value pad or terminator is recommended.
✓
Reverse: Terminate all low value tap ports. Even an un-terminated splitter in a
subscriber's house a few thousand feet away can cause standing waves.
Coax attenuation at lower frequencies is slight, which allows the reflected
wave to make it back without much loss.
✓
Reverse: Install a terminating tap (4 port 8 or 8 port 11) if possible. It is an
easy way to isolate the system.
Suck-Outs
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Typically caused by grounding issues or
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Multiple impedance mismatches at perfect intervals
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Sometimes manifests as spikes due to signals adding in-phase
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Spikes are also caused by oscillations and ingress
High End Roll-Off
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Associated with bad accessories, water, cracked cable
sheath, or amplifier band-edge roll-off
Spikes (sweep points)
✓
Keep resolution to approximately 8 MHz for forward sweep
✓
Reduces chance of inadvertent, overlapping sweep points and transients
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A sweep point every 8 MHz is sufficient in most situations for forward sweeping
✓
Also means faster sweep update and less memory required for each stored trace
✓
Verify proper set-up, levels, channel types, no overlapping sweep and actual
channels, etc
✓
Avoid common problem areas such as strong off-air broadcasts and certain FM
channels; (in return band, strong off-air shortwave, ham, and CB at 27 MHz)
✓
Reverse: Keep the resolution to approximately 1 MHz for reverse sweep
Common Sweep Issues ─ Bad sweep Response
✓
Verify accessories are operating correctly such as cable, push-ons, pads, etc.
✓
Low sweep points may get confused with noise floor especially after going through
more actives with associated noise figures. This could cause "grassy" effect on
sweep display. Increase sweep insertion level on the SCU-1800 to verify.
✓
Use correct Sweep mode. Selecting wrong mode can lead to problems.
✓
If input levels are too high, this may cause extreme intermodulation distortions,
which can affect the associated sweep points
✓
ONX-630 or DSAM sweep will function only with SDA Compatible mode selected
on SDA-5500 transceiver (SCU-1800 requires no configuration for this)
✓
High forward levels into meter can cause intermodulation that can affect reverse
sweep
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