MFJ-1026 Instruction Manual
Deluxe Noise Canceling Signal Enhancer
3
When peaking or adding signals, best performance occurs when signals have equal and the best possible
signal-to-noise ratios on both antennas. When adding desired signals, it is preferable to locate both the
MAIN and AUXILIARY antennas as far from local noise sources as possible. Adding desired signals
from a "noisy antenna" into a "quiet antenna's" signal will only make things worse. In the case where one
antenna is significantly noisier than the other, use the quiet antenna for the signal and cancel any noise
with the "noisy antenna".
If the desired application is the removal of distant interference,
close spacing is desirable. Close
spacing produces a wider and more stable null. Spacings of one half wavelength
or less
are most
desirable when nulling distant interference or peaking distant signals.
If the primary problem is removal of local noise,
it is preferable the noise (AUXILIARY) antenna
"hear" the noise much louder than it hears desired signals. The noise antenna should be located as close
to the noise source as possible, so the noise antenna picks up the least amount of desired signal and
largest amount of noise possible. In this case the polarization is unimportant, and the spacing between
antennas can be any convenient distance.
Circuit Description
The MFJ-1026 contains a noise amplifier, bridge-type phasing circuit, active combiner, and transmitter
change over relay circuit. The noise pre-amplifier consists of Q9 and Q10. Two jumpers, JMP1 and
JMP2 (see Figure 1), are provided to allow the preamplifier to be used with the external AUXILIARY
ANTENNA connection.
When both JMP1 and JMP2 are "off" or not active, the front panel pre-amplifier switch selects either the
internal whip antenna (PRE-AMP ON position of SW4) or the external AUXILIARY ANTENNA (PRE-
AMP OFF position).
The MFJ-1026 contains internal high-pass filters that begin to roll off on the 160 meter band. These
filters can be bypassed if AM broadcast band interference is not a problem., but the phasing control will
have limited range below 1.5 MHz. With suitable modification the MFJ-1026 will cover from 100 kHz
to 1.6 MHz, or any other 16:1 frequency range between 100 kHz and 35 MHz.
When JMP1 is "on" or active, the internal whip is not used and maximum external amplifier gain is
selected. When only JMP2 is "on" or activated, external AUXILIARY ANTENNA gain is moderate. In
these cases, the PRE-AMP switch either inserts or bypasses the internal amplifier consisting of Q9 and
Q10.
Q8 always drives the bridge-type phasing control.
The PHASE control, R16, allows signals from the AUXILIARY antenna (or internal whip) to be rotated
in phase nearly 180 degrees (
φ
>145 degrees) over the entire 1.8 to 30 MHz spectrum. PHASE switch
(SW3) allows the selection of either zero (NORMAL) or 180 degrees (INVERT) of additional phase by
selecting the signal from Q7's source or drain. The total phase shift range is the sum of the PHASE
control delay and the delay selected by the PHASE switch.
