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MFJ-936C

Deluxe High-Efficiency Magnetic Loop Tuner

Instruction & Technical Manual

7.

COAX OUTPUT:

This is one of two

output

ports for using a coax loop instead of wire.

8.

PVC MOUNT:

This is the mount point for the PCV cross assembly.

The MFJ-936C

Deluxe High-Efficiency Magnetic Loop Tuner

Rear Panel connections function to

permit connecting the wire loop at the output, and connecting the coaxial line at the input of the
tuner. Refer to Figure and the labeled component locations.

Figure 5: Rear-panel Connections: 1.) Wire loop connectors, 2.) Coax input

1.

LOOP CONNECTORS:

Connect wire loops here.

2.

COAX INPUT:

Connection to transceiver.

A wire loop antenna connects to the Loop Connectors with the two wing nuts provided on the
Loop Connector standoff rods. RF from the transceiver is input at the rear coax port. Care must
be taken not to disturb the wires leading from the lugs on the Loop Connector stand-off rods and
entering through the back of the tuner. The connection points must be kept clean at all times.
This unit is

not

intended for outdoor installation except during portable operation and must be

protected from the elements.

3

LOOP THEORY

A magnetic loop antenna is one that is characterized by low-noise reception, working well even
when mounted at ground level, and a circumference of less than

1

/

3

wavelength. The ideal small

transmitting antenna would have performance equal to a large antenna, and the MFJ-936C
approaches that performance. Bandwidth is quite narrow due to the extreme high-Q of the
tuned-circuit configuration when paired with a capacitor.

The components in a resonant transmitting loop are subjected to high currents and voltages
because of the large circulating currents in the high-Q tuned circuit formed by the antenna. It is
very important that the capacitors used in this antenna have a high RF current rating. Even a
100W transmitter develops currents in the tens of amperes, and voltages across the tuning
capacitor can be greater than 10kV. This consideration also applies to any conductors used to

-8-

Summary of Contents for MFJ-936C

Page 1: ...Deluxe High Efficiency Magnetic Loop Tuner MFJ 936C INSTRUCTION MANUAL 2020 MFJ Enterprises Inc 300 Industrial Park Rd Starkville MS 39759 P 662 323 5869 F 662 323 6551 ...

Page 2: ...onal handbooks or other official publications The copy of this manual provided to the customer will not be updated to reflect current data Customers using this manual should report errors or omissions recommendations for improvements or other comments to MFJ Enterprises 300 Industrial Park Road Starkville MS 39759 Phone 662 323 5869 Fax 662 323 6551 Business hours M F 8 00 AM 4 30 PM CST CDT ...

Page 3: ...STEM SETUP 9 4 1 LOOP CONSTRUCTION 9 4 2 CONFIGURATION 10 5 SYSTEM OPERATION 10 5 1 DETAILED OPERATION INSTRUCTIONS 11 5 2 QUICK START INSTRUCTIONS 12 5 3 MFJ 936C ACCESSORIES 14 6 TECHNICAL ASSISTANCE 14 List of Figures 1 An Electromagnetic Plane Wave 2 2 The Electromagnetic Spectrum 3 3 The MFJ 936C 6 4 Front Panel 7 5 Rear Panel 8 6 Typical MFJ 936C Configuration 10 List of Tables 1 100W Indoor...

Page 4: ...y RF energy is one type of electromagnetic energy Electromagnetic waves and associated phenomena can be discussed in terms of energy radiation or fields Electromagnetic radiation is defined as waves of electric and magnetic energy moving together or radiating through space The movement of electrical charges generates these waves For example the movement of charge in a radio station antenna the alt...

Page 5: ...ons are usually characterized by their approximate corresponding wavelengths such as 12 15 17 20 meters et cetera The electromagnetic spectrum Figure 2 includes all of the various energies of electromagnetic radiation ranging from extremely low frequency ELF ranges with very long wavelengths to all the way up to x rays and γ rays which have very high frequencies and correspondingly short wavelengt...

Page 6: ... exposure to radio frequency electromagnetic fields However Supplement B users should also consult Bulletin 65 for complete information on FCC policies guidelines and compliance related issues Def initions of terms used in this supplement appear in Bulletin 65 Bulletin 65 can be viewed and downloaded from the FCC s Office of Engineering and Technology s website at https www fcc gov general radio f...

Page 7: ...re members of the general public always fall under this category when exposure is not employment related as in the case of residents in an area near a broadcast tower Neighbors of amateurs and other non household members would normally be subject to the general population uncontrolled exposure limits 1 6 OPERATING ENVIRONMENTS GUIDELINES Tables 1 and 2 list various MFJ 936C Deluxe High Efficiency ...

Page 8: ... 03 0 93 4 06 1 23 1 3 07 0 93 4 95 1 50 3 24 0 3 23 0 98 5 48 1 66 1 3 37 1 02 5 51 1 67 3 28 0 3 47 1 05 6 04 1 83 1 3 47 1 05 6 04 1 83 3 Table 2 150W Indoor and Outdoor Operating Environment Frequency MHz Controlled Population Exposure ft m Uncontrolled Population Exposure ft m Height m 7 0 1 45 0 44 2 05 0 62 1 1 52 0 46 3 00 0 91 3 10 0 2 28 0 69 3 00 0 91 1 2 77 0 84 3 66 1 11 3 14 0 2 87 0...

Page 9: ...smitting loop circuit to your 50Ω coaxial cable Figure 3 The MFJ 936C RF grounds radials or a counterpoise system are not required though a safety ground is recommended While the MFJ 936C Deluxe High Efficiency Magnetic Loop Tuner can tune any shape loop circle square rectangle or any odd shape a wire or length of coaxial cable approaching a quarter wavelength shaped as a circle is the most effici...

Page 10: ...hotel rooms antenna restricted and portable locations 2 3 CONTROLS CONNECTIONS The MFJ 936C Deluxe High Efficiency Magnetic Loop Tuner front panel controls and indicators Figure 4 function to permit matching the wire or coax loop to the coaxial line at the input of the tuner Figure 4 Front panel Controls 1 Tuning Control 2 Matching Control 3 Power Range 4 Meter Sensitivity 5 SWR Meter 6 Antenna Cu...

Page 11: ...tering through the back of the tuner The connection points must be kept clean at all times This unit is not intended for outdoor installation except during portable operation and must be protected from the elements 3 LOOP THEORY A magnetic loop antenna is one that is characterized by low noise reception working well even when mounted at ground level and a circumference of less than 1 3 wavelength ...

Page 12: ...hese bands However below 14 MHz ground losses become significant and will noticeably degrade the performance of the MFJ 936C when placed close to the ground If elevating the MFJ 936C is not an option the loop should be mounted vertically It is possible to improve the efficiency of the loop antenna through the use of freeware antenna modeling software Use the software to create a model of the anten...

Page 13: ... at QRP levels 4 2 CONFIGURATION Setting up the MFJ 936C Deluxe High Efficiency Magnetic Loop Tuner Figure 6 is simple and consists of the following components RF Source Transmitter Transceiver SWR Wattmeter MFJ 936C Deluxe High Efficiency Magnetic Loop Tuner Coaxial cable s 10 gauge or larger stranded wire cut to approximately 20 of the full wavelength at the chosen frequency Figure 6 Typical MFJ...

Page 14: ...spin a wire loop to a curtain around a window frame A circle encloses the maximum area Otherwise drape it across bookcases or similar non conductive objects to fashion a loop of sorts to use If the loop antenna is rigid then place it in a position to accommodate its particular shape and size The MFJ 57B or MFJ 58B make this simple by providing a precut PVC frame and wire lengths Step 3 Setup the M...

Page 15: ...f the FCC OET Bulletin 65 version 97 01 are met Should any arcing be detected stop transmitting and check connections and proximity to objects that may be suspect If arcing seems to be inside of the MFJ 936C lower the output power and re check for arcing As a courtesy to our fellow hams for safety and to stay within FCC regulations you should use the minimum power needed for communications Power l...

Page 16: ...osition for the controls and switches is found Step 5 Apply 10 to 20 Watts of power to the MFJ 936C and adjust the TUNING control for maximum RF current and the MATCHING control for minimum SWR on your external SWR Wattmeter Readjust the TUNING control for maximum RF current Repeat this sequence until you see no further improvement in minimum SWR and maximum RF current Be sure to adjust the RF cur...

Page 17: ...ing a precut and lugged wire loop to the top cover of the tuner This flexible 10 gauge wire loop covers 20 and 30 meters and the ends have low resistance lugs The MFJ 58B which contains all of the MFJ 57 items plus 40 meter 15 20 meter and 10 17 meter wire loops with clips to hang loops as needed 6 TECHNICAL ASSISTANCE If you have any problem with this unit first check the appropriate section of t...

Page 18: ...USER NOTES ...

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