MFJ MFJ-1026 User Manual

MFJ-1026 Instruction Manual

Deluxe Noise Canceling Signal Enhancer

MFJ-1026

MFJ Deluxe Noise Canceling Signal Enhancer

Instruction Manual

Introduction

To get the best performance from your MFJ-1026, read this manual. It is especially important to heed all warnings to prevent equipment damage.

The MFJ-1026 is designed to reduce noise or interference, or improve desired signals, before the noise affects sensitive receiver circuits. Unlike conventional noise blankers, the MFJ-1026 can be effective on all types of noise, including interference (QRM) from unwanted signals. The MFJ-1026 allows the user to adjust both phase and amplitude while combining two antenna inputs. The antenna inputs can be from two external antennas, or an external antenna and the MFJ-1026 internal whip antenna. The signal output for the receiver is the vector addition or subtraction of signals from two separate antennas. This allows unwanted noise to be removed or desired signals to be enhanced. The MFJ-1026 is optimized over the range of 1.8 to 30 MHz.

The phasing method of signal enhancement or null removal has several advantages over conventional noise blankers. The advantages are:

1.Interference can be much stronger than the signal and be completely removed without affecting the desired signal.

2.The MFJ-1026 can be effective with all types of interference and on all modes.

3.Signals can be added instead of subtracted with the simple push of a button.

The circuitry in the MFJ-1026 has exceptional phase amplitude flatness, making adjustments easy and very repeatable. Typical phasing systems provide either limited phase adjustment range, or changes the signal's level as phase is adjusted. In the MFJ-1026, gain changes less than 3 dB (and typically less than 1 dB) as the phase control is rotated throughout its range.

Effective and proper operation occurs only when the same noise (for nulling noise) or desired signal (for signal enhancement) is present on both the AUXILIARY (or internal whip antenna) and MAIN antennas. If the interfering source is not audible on the internal whip antenna, the MFJ-1026 has provisions for using an external noise antenna (labeled "AUXILIARY ANTENNA" on the rear panel). In most cases, it will be necessary to use the external AUXILIARY ANTENNA input.

The MFJ-1026 contains interface circuitry necessary for operation with most modern HF transceivers. Although the MFJ-1026 contains internal T/R (transmit-receive) RF sensing, we STRONGLY recommend using the external T/R Control line on the rear panel for keying the MFJ-1026.

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MFJ-1026 Instruction Manual

Deluxe Noise Canceling Signal Enhancer

Failure to use the external control line can result in slow transmitter power rise, or damage to the MFJ1026 components. This is especially true when a transmitter has fast envelope rise time, or has power "overshoot" on the leading edge of the RF envelope. Some exciters overshoot to as much as 350 watts on key closure before settling down to rated power.

Theory of Operation

It is commonly perceived that noise interacts with an antenna differently than a "desired" signal. Noise that propagates over even short distances is an electromagnetic wave. Noise influences the antenna exactly the same as desired signals. Noise also follows the same rules of propagation as the signals from our transmitters. Noise does not have to be local in origin, it can also arrive by ionospheric propagation from distant sources. This effect can allow noise from sources thousands of miles away to accumulate at the receiving location and "mask" weak signals.

The MFJ-1026 allows you to create a "phased antenna system" out of nearly any pair of antennas. Since noise and signals all behave the same way before the receiver, this fully adjustable phasing box can be used to cancel or null unwanted signals, noise, or interference as well as enhance desired signals.

IMPORTANT:

The MFJ-1026 allows almost any combination of antennas to be used as a system, but the MFJ-1026 works best when the main and noise antennas have the same basic patterns when nulling or peaking distance noise or signals. That means the antennas should be oriented in the same direction and also have the same basic polarization for best performance.

It is not necessary to use any special length of feedline with the antennas, or for the antennas to be "resonant" or physically large. Lower Q and smaller antennas often produce the most stable and reliable performance. Failure to follow this basic guideline will often decrease performance when nulling or peaking distant signals.

The MFJ-1026 has four primary advantages over typical phased antenna systems:

1.The user can electrically "rotate" the array, even though the antennas remain physically stationary.

2.The user can adjust both direction and wave angle of the null or peak.

3.The user can change from nulling a signal to peaking a signal with the push of a button.

4.Mutual coupling effects can be ignored as phase and level controls are adjusted.

When adding desired signals, the noise and main antennas must both "hear" the desired signal. It is preferable that both antennas be reasonably close together (within a wavelength) and of similar polarization. Mixing a vertical antenna with a horizontal will almost always increase fading (contrary to false rumors that it decreases fading) over an ionospheric path.

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MFJ-1026 Instruction Manual

Deluxe Noise Canceling Signal Enhancer

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 (PREAMP 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.

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MFJ-1026 Instruction Manual

Deluxe Noise Canceling Signal Enhancer

Q5 and 6 form the active combiner, and Q4 is a line driver supplying output to the receiver.

Q1, Q2 and Q3 are part of RF sensing circuitry. They are included to automatically bypass the MFJ-1026 during transmissions, although we HIGHLY recommend using the rear panel T/R CONTROL line input whenever possible.

Figure 1

Rear Panel Connections

The MFJ-1026 has a variety of connections on the rear panel. From left to right the connections are:

GND: This connection is used to connect the MFJ-1026 to the station ground buss. Always use a short ground wire when making this connection. Always try to use solid copper wire (not braided wire) when making a ground connection. Woven or braided wire has higher RF resistance than solid conductors.

MAIN ANTENNA: This SO-239 provides a direct connection to the RADIO connector whenever power is removed, if the external T/R CONTROL jack is grounded, or if transmitter power is applied. This connector should connect to the input of the station's power amplifier or to the rest of the station accessories, such as wattmeters or antenna tuners.

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MFJ-1026 Instruction Manual

Deluxe Noise Canceling Signal Enhancer

RADIO: This SO-239 has a direct connection to the MAIN ANTENNA connector when power is removed, if the external T/R CONTROL jack is grounded, or transmitter power is applied. This connector should always be connected to the receiver's input connector or to the transceiver's "antenna" connector.

T/R CONTROL: We STRONGLY recommend using this phono connector to switch the MFJ-1026 to the transmit (or bypass) mode. The MFJ-1026 switches out-of-circuit whenever this line is pulled low (below one volt). Never apply negative voltages, or voltages over 15 volts positive, to this jack.

WARNING: We strongly recommend using this connection to switch the MFJ-1026 into the transmit mode!! Many radios have sharp transmitter rise times or power pulses that, at times, cause damage to the MFJ-1026.

AUXILIARY ANTENNA: This SO-239 and the phono jack to its immediate right are inputs for the auxiliary receive or noise antenna system.

POWER: This 2.1mm coaxial power connector requires a nominal supply voltage of twelve volts at approximately 150 mA. The center pin is positive.

CAUTION: Do not reverse the power connections or damage will result. Remember, the center pin is positive, and the outer shell is negative.

Front Panel Controls

The MFJ-1026 has several user controls on the front panel. From left to right, the front panel controls are:

POWER ON/OFF: This switch turns the main power off and on. In the OFF (out) position, the MFJ1026 is bypassed. The RADIO and MAIN ANTENNA connectors have a direct connection between each other whenever power is removed or this switch is turned off.

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