MFJ-259 Instruction Manual
HF/VHF SWR Analyzer
6
severely damaged
.
A coupling loop is useful for directing RF at a reduced level into the
counter. A coil of wire, or even a straight piece of wire attached to the BNC connector may
be sufficient for operation. The length and number of turns will vary with the power supplied
by the transmitter. A weak signal will require a larger area of wire to supply a good level to
the counter, compared to a powerful transmitter.
A standard HT antenna, which has a BNC connector, may act as a conductor of RF into the
counter. An antenna with no loading coils is preferred to one which does. A 2 meter antenna
may not conduct enough energy to the counter if it is used on the HF bands. Antenna
attenuation can greatly reduce the RF level into the counter. The coupling antenna may have
to be much closer to the transmitting antenna if the transmit level is low. On a high power
transmitter, the coupling level may be useful for quite a distance from the transmitter.
Coupling of the RF signal into the counter may also be done by placing several turns of wire
around a coax feedline, and attaching it to the counter input. More turns will be needed for a
well-shielded cable than for a lossy cable. Hard-line is not usable since there is no leakage.
The leakage from the cable is usable under normal conditions for a low level counter input.
Experimentation will be needed to determine how many turns are needed for a particular
installation.
A loop of wire placed inside the case of a wattmeter, dummy load, low-pass filter, etc., is
another way to couple RF into the counter. The inductance of the loop will act as an antenna,
to direct low level RF into the counter. Almost any type of wire may act as a receiving
antenna for coupling RF into the counter.
The sample time period is selected by momentarily pressing the "GATE" button near the
upper left corner of the top panel. The counter displays the average frequency over the sample
time period. The red LED in the upper right corner of the front panel flashes when the count
cycle is complete and the display is updated.The blinking LED will speed up and/or slow
down with the changing of gate settings. At power up, the sample time period normalizes at
.01 seconds. Additional count periods of 0.1, 1.0, and 10 seconds can also be selected.
Connect the cable with the signal to be counted to the BNC type jack labeled "FREQUENCY
COUNTER INPUT".
Gate Settings
Gate Setting
Gate Time
Measurement
Time
Measurement
Resolution
Example
1
10 mS
25 mS
100 Hz
162.5500
2
100 mS
130 mS
10 Hz
162.55000
3
1 S
1 S
1 Hz
162.550000
4
10 S
10 S
0.1 Hz
162.5500000