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19
splatter or similar spillover from an adjacent station, or even
modulation from a distant station on the same frequency.
Noise is quantified on an arbitrary numerical scale of zero to
nine with the bargraph scaled proportionally. Anything over a
value of 2 gives reason to suspect the accuracy of modulation
measurement. Aiming the antenna away from an offending
source may help reduce the noise contribution.
Metered noise is not the only non-program component that can
sabotage modulation readings. Impulse noise and other spuri-
ous signals that may happen to be in phase with the received
carrier at a particular instant may not show up on the
NOISE:
scale. Use your ears to identify and qualify this type of inter-
ference.
Impulse noise will tend to inflate the reading of positive carrier
modulation, while adjacent-channel spillover will cause both
positive and negative indications to read high.
SETTING THE PEAK FLASHERS
The 525N has two sets of front-panel LED peak flashers to show
overmodulation. The larger top and bottom red LEDs indicate
the absolute US (and some other coutries’) legal limits of –100%
and +125% modulation. The two smaller yellow LEDs may be
programmed by the user to show when alternative values are
exceeded.
Scroll down to Menu No. 4,
SET PK FLASH
. Use the
SEL
but-
tons to bracket each flasher trip point, and then the
MENU/EDIT
buttons to set these to any desired value.
Peak flashers are programmed with 1% resolution and settings
are held in non-volatile memory. Exit the setup process by
pressing SEL until neither number is bracketed, and then navi-
gate out of the screen with the MENU/EDIT buttons. Do noth-
ing and the screen will revert to the home
PEAK MODULATION
screen after 30 seconds.
THE OVERMODULATION ALARM
Carrier overmodulation is either a condition of carrier cutoff,
or –100% modulation, or positive modulation peaks reaching
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