MFJ MFJ-208 User Manual

MFJ-208 VHF SWR Analyzer

Thank you for purchasing the MFJ-208 VHF SWR Analyzer. The
MFJ-208 gives you a direct readout of your antenna's SWR
without the need for formulas or indirect readings. The MFJ­208 can also be used to adjust a tuner to match your antenna
without the need for transmitting. The frequency coverage for
the MFJ-208 is from approximately 142 MHz to 156 MHz.

The MFJ-208 requires the MFJ-1312 power supply adapter

(optional) or a nine-volt transistor battery.

To install a battery, remove the screws holding on the cover.
Insert the battery into the battery holder. Tuck the battery
snap wires out of the way so they do not interfere with the
tuning capacitor rotation. Re-install the cover and screws. The
dial calibration is only approximate and is for reference only.
A frequency counter can be connected to the FREQ. OUT jack
(RCA phono) to get a more accurate reading of the frequency.
As an alternative to a frequency counter, you can zero beat
the output with an VHF receiver. See APPENDIX A.

USING THE MFJ-208 VHF SWR ANALYZER

Your MFJ-208 VHF SWR Analyzer has many uses. It can be used
to find the resonant frequency of your antenna, to find the SWR
of your antenna at a particular frequency, find the frequency
at which your antenna has the lowest SWR. You can also use the
SWR Analyzer to adjust your antenna to a low SWR and to adjust
an antenna tuner (MFJ-921 or MFJ-920) to match the transmitter
to the line.

Measurement of the antenna's SWR is done right at the
input to the transmission line. There is no need to climb the
tower and measure the SWR at the antenna. Using the chart in
Figure 3, and knowing the line loss for your transmission line
and the SWR at the line input, you can determine the SWR at the
antenna, regardless of line length

or line loss.

I. Measure the antenna's SWR at a particular frequency.

1. To check the SWR of your antenna, connect the
antenna with a PL-259 connector to the ANTENNA
connector on the MFJ-208.

NOTE: If you are using coax as your feedline, connect

the coax directly to the UHF connector marked ANTENNA.
If you are using an open-wire feedline, wire the
feedline to a PL-259 connector, then attach it to
the ANTENNA connector of the MFJ-208.

2. Push the power button to ON. The LED should light. 3.

Adjust the frequency dial of the SWR ANALYZER to

read the frequency at which you want to check the
SWR.

4. Read the SWR from the meter.
This is the SWR at the INPUT TO THE TRANSMISSION
line looking toward the load (antenna). To

determine the SWR at the antenna, use Figure 3 in
APPENDIX D.

5. Using steps 1 through 5, you can make a plot of
SWR versus FREQUENCY for your antenna. Just plot
the SWR at many different frequencies. APPENDIX B
has an SWR vs. FREQUENCY chart. We suggest you
make photocopies of this chart so you can use it
for several antennas.

II. Find the frequency at which the antenna has the

lowest SWR.

1. Connect the antenna to the MFJ-208 as in step I.

2. Push the power button to ON.

3. Adjust the TUNE control throughout its range until
the SWR meter reads its lowest value. Read the

frequency on the tuning dial. Read the SWR on the

meter.

III. Adjust the antenna for 1:1 SWR.

1. Turn the frequency TUNE knob until the pointer is
on the freq at which you want to tune the antenna.

NOTE: For accuracy, use a frequency counter attached to the

COUNTER output on the SWR ANALYZER or zero-beat
against the receiver.

2. Read the SWR on the meter. If the meter reads
other than 1:1 SWR, adjust the antenna until the
antenna reads 1:1 SWR (or lowest value obtainable).

NOTE: The MFJ-208 can tell you whether the antenna elements

are too short or too long. If you find the
antenna's resonant frequency is too low, then the
elements are too long. If the resonant frequency is
higher than you want, then the elements are too
short.

If you are adjusting an antenna for the first time, it is
recommended you start with elements a little too long, then
shorten to resonance. Again, the SWR for your particular
antenna may never get as low as 1:1. Adjust for the lowest
reading.

IV. Using the MFJ-208 to adjust an antenna tuner.

1. Connect the antenna to the antenna tuner connector
marked ANTENNA, then connect the tuner connector
marked TRANSMITTER to the MFJ-208 connector marked
ANTENNA.

2. Push the power to the ON position.

3. Set the frequency dial to the desired operating
frequency. Adjust the tuner's controls until the

meter on the MFJ-208 indicates 1:1 SWR (nulls).

4. Disconnect the MFJ-208 completely and connect the
tuner to the transmitter.

5. Push the power switch to the OFF position when
you are finished checking the SWR.