MFJ MFJ-1668 User Manual

MFJ-1668 Instruction Manual Screwdriver Antenna

MFJ 1668 MOBILE SCREWDRIVER ANTENNA

Introduction

The MFJ-1668 manually tuned screwdriver antenna was designed for continuous operation from
6-80 meters using a supplied whip 10 feet in length. The supplied 4 ½ foot whip can be used for
mobile or limited space operation.

The antenna is tuned by loosening a thumbscrew and moving the aluminum cover up or down the
loading coil. The loading coil is made of tin plated copper wire wound onto a PVC pipe core.
Copper Beryllium finger-stock is used to make the connection between the aluminum cover and
the loading coil.

WARNING: SERIOUS RF BURNS AND INJURY CAN OCCUR IF CONTACT IS
MADE WITH THE ANTENNA. PLACE THE ANTENNA IN AN OUT OF
REACH LOCATION.

Portable Operation And Mounting

The MFJ-1668 becomes a very efficient portable antenna when used in combination with a tripod
and a ground radial system. The antenna can be easily mounted onto a tripod such as the MFJ­1918 or similar mount for portable operations. The MFJ-342 3/8 pipe mount easily attaches the
antenna to a tripod. The antenna must be properly connected to a ground radial system.

Portable Setup

1. Remove the antenna from the packaging.

2. Place a 3/8“ lock washer onto the 3/8 X 24 thread of the desired whip.

3. Carefully screw the desired whip into the 3/8 coupling nut located on top of the loading
coil.

4. Secure the whip in place with a 9/16 wrench.

5. Place a 3/8” lock washer onto the 3/8 X 24 mount on the base of the loading coil.

6. Screw the antenna into the desired mount 3/8 X 24 female mount such as the MFJ-342.

7. Secure the antenna in place using a 9/16” wrench.

8. Attach the counterpoise system to the ground shield of the feed-line. If using a MFJ-342
or similar mount attach the ground radials to one of the ¼” bolts located on the mount.
Check to make sure the ground system does not come into contact with the screwdriver
antenna.

Mobile Operation

The MFJ-1668 may be used as a mobile antenna by connecting the supplied 4.5 foot whip
onto the antenna. Also the 10-foot whip may be used when the vehicle is parked for
greater efficiency. NEVER ATTEMPT TO USE THE 10-FOOT WHIP WHILE A

VEHICLE IS IN MOTION. DAMAGE OR SERIOUS INJURY CAN AND WILL
OCCUR IF THE ANTENNA COMES INTO CONTACT WITH OVERHEAD
OBSTRUCTIONS OR POWER LINES.

MFJ-1668 Instruction Manual Screwdriver Antenna

Mobile Setup

1. Remove the antenna from the packaging.

2. Place a 3/8“ lock washer onto the 3/8 X 24 thread of the desired whip. ALWAYS USE
LOCK WASHERS FOR MOBILE INSTALLATIONS.

3. Carefully screw the desired whip into the 3/8 coupling nut located on top of the loading
coil.

4. Secure the whip in place with a 9/16 wrench.

5. Place a 3/8” lock washer onto the 3/8 X 24 mount on the base of the loading coil.
ALWAYS USE LOCK WASHERS FOR MOBILE INSTALLATIONS.

6. Screw the antenna into the desired mount.

7. Secure the antenna in place using a 9/16” wrench.

8. Attach a vehicle ground to the ground shield of the feed-line. The ground should be
attached directly to the vehicle frame or body. Check to make sure the ground system
does not come into contact with the screwdriver antenna.

Impedance Matching

For proper feed-point matching and operation, an impedance matching coil will need to be place
between the antenna and a ground. This will be more necessary for the lower HF bands such as
40 and 80 meters. Attach one end of an impedance matching coil to the wing nut on the lower
part of the antenna. Attach the opposite end to the ground radial system or vehicle ground
attached to the coax shield depending on your installation.

Tuning

The MFJ-1668 can be tuned very easily using a SWR analyzer such as the MFJ-259B. A radio
and an SWR METER may also be used. The resonant frequency of the antenna is adjusted by
loosening the thumbscrew located on the side of the antenna. The antenna should be setup in the
desired operating location using the instructions above. The ground system must also be installed
for proper operation. Follow the steps below to choose the desired operating frequency.

1. Check to see that the antenna is setup properly as instructed above.

2. Extend the whip to the full length.

3. Check the resonance point (a minimum SWR) of the antenna with the coil completely
shorted out. The coil is completely shorted when the coil is completely covered.

4. If a resonance point cannot be found check all of your connections including your ground
radial system.

5. To lower the operating frequency loosen the thumbscrew and slide the coil cover down
the coil. To increase the resonant frequency slide the coil cover up the antenna. Tighten
the thumbscrew and check the SWR as was done in step 3.

6.

When the desired frequency is obtained tighten the thumb screw. Repeat the
above steps to find additional operating frequencies.