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	MFJ-

208 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

to

Your MFJ-208 VHF SWR Analyzer has many uses. It can be used

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.