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Phase Nulling with a Transmit Antenna
As described throughout this manual, the primary advantage of using receiving antennas for phase
nulling of unwanted signals is to enhance the signal to noise ratio (S/N) of the desired weak signal.
Wherever possible, the use of low signal, low noise receiving antennas will generally produce
superior results, especially with the
NCC-1
.
HF and Low Band (160, 80, 40 meters) transmitting antennas usually receive high levels of noise
and when used for phasing, the result is a noisy signal.
However, there are cases where phasing with a transmit antenna is desired. Some fortunate
Amateur Radio Operators reside in locations where the ambient noise levels on their transmit
antenna is low enough that their benefits from phase nulling and peaking will be maximized.
Many radio enthusiasts live in areas where some type of noise or strong signal interference is
preventing normal or weak signal DX receive operations. Some Amateur Radio Operators must use
a transmit antenna for nulling out undesired signals because receive only antennas will not 'hear' the
desired signal. Many of the low noise advantages of the
NCC-1
will be hidden by strong ambient
noise if a transmit antenna is used as a receive antenna for the
NCC-1
.
If your transceiver has both Receive Antenna Input (RX IN or RX ANT)
and
a Receive Output (RX
OUT), you may use the transmit antenna receive signals that are available from that port for phasing
the transmit antenna against those from a receive antenna.
Figure 3
demonstrates the connection
scheme for phasing a receive antenna against a transmit antenna. Special adjustments to the
attenuator and balance may be required. Additional attenuation of the RX Out to INPUT B may be
required in certain conditions, so the signal or noise level coming from the transmit antenna does
not override the signal or noise level coming from the receive or noise "sense" antenna.
If used, active antenna power may be derived internally from the
NCC-1
and is automatically
disconnected during transmit by setting jumpers HD1 and HD4 per the chart listed in
Figure 3
.
If a non-powered, passive receive antenna is used, jumpers should be in the default position as
supplied. Refer to
Figure 1
.
