MFJ MFJ-974 Скачать руководство пользователя страница 3

MFJ-974/974H Balanced Line Antenna Tuner 

Instruction Manual 

Installation

 

 
 
 
 
 

1.

  Place the tuner in a convenient location at the operating position. With  random wire or balanced feedlines, 

the feed through insulators may have high RF voltages. These voltages can cause serious RF burns if the 
terminals are touched when transmitting.  

Be sure to locate the tuner so these terminals cannot 

accidentally be contacted during operation. 

2.

  Install the tuner between the transmitter and the antenna.  Use a 50-ohm coaxial cable (such as RG-8/U) to 

connect the transmitter to the connector marked 

TRANSMITTER

 on the rear of the tuner. 

3.

  Connect the antenna feedline to the tuner as follows: 

A.

  Coaxial feedlines connect to the coax connector labeled 

ANTENNA

 (a jumper wire is required between 

the lower, red binding post and the ground terminal). 

B.

  Random wire or single wire line antennas should be connected to the top red connector on the back of 

the unit (jumper wire required between the lower, red binding post and the ground terminal). 

Note:

  Route all single and random wire antennas safely to prevent RF burn hazard. 

C.

  Balanced feedline (open wire, twinlead, or twin-axial line) is connected to the 

BALANCED LINE

 

terminals. 

4.

  A ground post is provided for an RF ground connection. 

 
 
 
 
 
 

 
 
Operation

 

 

The MFJ-974H uses three inductors for maximum efficiency. A 2½-inch diameter high-Q air-wound inductor is 
tapped for flexibility and is used on frequencies from 3.5 to 30 MHz. For 160 Meters (

MFJ-974H

 only) an 

additional inductance, made of Teflon™ insulated wire wound on two powdered-iron cores, is switched in by the 
front panel 

160 METER

 pushbutton. Front panel inductor switch position L automatically selects a 6-Meter only 

inductance (bypassing the larger air-wound coil).  Inductance switch position A is the greatest inductance, 
position L the least. The inductance decreases as the knob is rotated clockwise. 
 
The 

ANTENNA 

and 

TRANSMITTER 

capacitors have 

maximum capacitance

 at setting 0 and 

minimum 

capacitance

 at setting 10.   

 
Maximum tuner efficiency is achieved with the most capacitance (settings closest to 0) and the least possible 
inductance (higher letters of the alphabet). This efficiency translates into best power handling, broadest 
bandwidth, and least power loss. The goal is always to operate the tuner at the lowest Q for the LC 
(inductance/capacitance) circuit. 
 

Transceiver or 

Transmitter

 

MFJ-974H/974

50-ohm coax

To antenna

RF ground

CAUTION 

Locate the tuner so the rear is not accessible during operation. 

Figure 1 
Block Diagram 

Содержание MFJ-974

Страница 1: ... arrays random wires and many other antennas The MFJ 974H has rear panel connectors for coaxial and single or two wire feedlines The built in balun works with balanced open wire twinlead or twin axial feedlines Understanding Power Ratings There are no standardized power rating systems for tuners The names used i e 3 kW Tuner carry over from the time when amplifiers were rated by peak power input a...

Страница 2: ...the true peak envelope power Forward power is displayed on the left hand FORWARD meter scale This scale is calibrated from 0 to 300 watts In the HI position each picket scale mark represents 5 watts below 10 watts 10 watts between 10 and 100 watts and 25 watts between 100 and 300 watts In the LO power position full scale meter reading is 30 watts divide the meter reading by 10 for the correct valu...

Страница 3: ...al line is connected to the BALANCED LINE terminals 4 A ground post is provided for an RF ground connection Operation The MFJ 974H uses three inductors for maximum efficiency A 2 inch diameter high Q air wound inductor is tapped for flexibility and is used on frequencies from 3 5 to 30 MHz For 160 Meters MFJ 974H only an additional inductance made of Teflon insulated wire wound on two powdered iro...

Страница 4: ...t and touch up the tuner settings if needed 8 For quick retuning of the tuner record the INDUCTOR and CAPACITOR settings for each band see the Logged Tuning Chart Page 10 Note Maximum power handling is achieved when both the ANTENNA and TRANSMITTER controls are set at the lowest possible number and the INDUCTOR control is set at the highest possible letter that permits matching the antenna Followi...

Страница 5: ... single wire feeder runs parallel and reasonably close to the wire that connects the tuner to the outdoor ground The antenna feed wire should be adequately insulated to prevent arcing or accidental contact For safety please use good DC and RF grounds It is particularly important to have a good RF ground when using a single wire feeder When using a single wire feeder the tuner needs something to pu...

Страница 6: ...e dipole s low impedance to over three thousand ohms at the tuner This is because the mismatched feedline is an odd multiple of 1 4 wavelength long The line inverts or teeter totters the antenna impedance A problem also occurs on 40 meters with this same antenna example The feedline is now a multiple of a half wave 60 to 70 foot and connects to a full wave high impedance antenna 100 to 140 feet Th...

Страница 7: ... Starkville MS 39759 by Facsimile FAX to 662 323 6551 or by email to techinfo mfjenterprises com Send a complete description of your problem an explanation of exactly how you are using your unit and a complete description of your station WARNING To avoid problems a dipole antenna should be a full half wavelength on the lowest band On 160 Meters an 80 or 40 Meter antenna fed the normal way will be ...

Страница 8: ...MFJ 974 974H Balanced Line Antenna Tuner Instruction Manual 8 ...

Страница 9: ... 1 5 E 3 25 3 75 2 E 2 50 3 75 2 E 1 5 600 4 0 0 F 0 25 4 0 1 F 0 50 4 0 1 F 1 600 7 15 0 I 2 5 25 7 15 1 I 0 50 7 15 1 5 I 1 5 600 10 1 0 K 2 5 25 10 1 1 K 0 50 10 1 0 K 1 600 14 2 3 L 4 25 14 2 4 L 3 50 14 2 4 L 3 600 18 1 6 5 L 7 5 25 18 1 6 L 6 50 18 1 7 L 7 600 21 2 7 5 L 7 5 25 21 2 7 5 L 7 5 50 21 2 7 L 7 5 600 24 9 8 5 L 8 5 25 24 9 8 5 L 8 5 50 24 9 9 K 8 600 28 5 8 5 L 9 25 28 5 9 L 9 50...

Страница 10: ...a Tuner Instruction Manual 10 Logged Tuning Chart Use the chart below to log values for your station You may want to copy this chart and post it by your tuner Frequency MHz ANTENNA INDUCTOR TRANSMITTER 1 8 3 5 7 10 1 14 18 21 24 28 50 ...

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