Application Notes: Reverse Sweep and Balance
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noise floor level on the reverse input and compare with the reverse
output. It should be higher by the amount of gain of the amplifier, but not
necessarily. The noise reading could be affected by the test equipment
noise floor. It may be warranted to inject a carrier and read the output to
verify continuity. Use "Diagnostics" to send a CW carrier to the headend.
Have someone in the headend use the Tx “Level” mode to read the
reverse carrier level. Be sure to put it back in “Sweep” mode when
finished!
• Reverse telemetry must have >20 dB S/N. To calculate the S/N for the
reverse, find the telemetry level at the headend read on the field unit
while sweeping, activate the "Noise" mode and move the marker to the
same frequency. Record the difference.
NOTE: The number of node returns is limited for the
Stealth reverse setup because the reverse telemetry signal
needs to have > 20 dB S/N. Probably less than 40 nodes
should be combined into the headend unit. This may also
influence where you place the telemetry. Stay away from 5-
15 MHz because of the inherent noisy nature of this
passband. Stay away from 27 MHz because of CB ingress
and any multiple of 6 MHz because of common path
distortions (CPD).
• Verify the instrument is sweeping in the correct direction. Press the left
diamond key and look in the upper right corner of the field unit display.
• Press "Sweep" on the Tx and make sure reverse is enabled. (Sometimes
it’s the little things that kill.)
• Firmware versions must be the same on the transmitters and receivers.
Bad Response
• Verify accessories are operating correctly such as cable, push-ons,
DDC-20, pads, etc.
• Low sweep points may get confused with the noise floor, especially from
the total noise funneling. This could cause the "grassy" effect on the
sweep display. Increase the sweep insertion level on the field unit to
verify.
• Use "Stealth" sweep instead of "Sweepless" sweep. The wrong mode
could lead to problems.
• High forward levels into the meter can cause severe intermodulation that
can affect the reverse sweep.
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