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desired or undesired directions, but there are cases where it can extend phase range and aid in
achieving a better null.
The PHASE NORM-REV switch will turn a NULL point into a PEAK point. Adjust for a null as
above, and then reverse the PHASE switch.
Unwanted signals or noise can only be nulled if present on both A and B antennas.
Desired signals can only be peaked if the have about the same S/N ratio on both antennas and when
spacing is correct.
Different fading rates and times between dissimilar or wide spaced antenna can make control
adjustment tedious.
The most stable and reliable nulls occur when antennas are moderately close together (between 1/10
and 1/4-wavelength apart), oriented in the same direction, and sharing the same polarization.
Using the NCC-1
The PHASE control changes the phase relationship between
A
and
B
INPUTs, effectively changing
the direction of a peak or null. When the phase control is fully counterclockwise, INPUT
A
has
minimum phase shift and INPUT B has maximum phase shift. As the PHASE control is rotated
clockwise phase shift in INPUT A increases while phase shift in INPUT B decreases.
The PHASE NORM-REV switch inserts zero (REV) or 180-degree (NORM) phase inversion in
INPUT B. This switch has the effect of changing a peak to a null, or a null to a peak. If a signal is
nulled with the NORM-REV switch in one position, changing the position will result in a peak.
It is best to know the approximate level from both antennas. If you are using greatly dissimilar
antenna levels dial in enough attenuation on the stronger antenna to approximately level signals.
If you have a general coverage receiver, select a strong steady signal between 1.5 and 30 MHz. The
ideal signal would be ground wave, although the time and frequency standards on 5, 7.335, and 10
MHz are good alternatives. Try to use a signal that does not have excessive or rapid fading.
If you know the signals from two antennas are not the same level:
A.
Connect antennas, Balance control in center, Set both attenuators on 0 dB.
B.
Tune in a strong clear station
C.
Dial 30 dB of attenuation in on INPUT B. The S meter reading is the level from A.
D.
Note this level.
E.
Before the signal has a chance to fade, remove attenuation from B (set to zero dB) and put
30 dB of attenuation on INPUT A.
F.
Note level. This is the level from B.
G.
The higher the S meter reading, more attenuation will be required. One S unit is typically
around 5 dB, although that number can range from 1-8 dB depending on the receiver and the
exact signal level. Set attenuators so the HIGHEST signal level port has the MOST
attenuation.
