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Para Dynamics
SWR Meter Instructions
3-Function Test Instrument - Model PDC 2
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Introduction
Model PDC 2 test instrument is a compact 3-function test meter designed to
indicate the condition of any 52 ohm antenna and antenna coax used for Citizens
Band radio operation by testing or Standing Wave Ratio, relative RF power,
or field strength. Tuning of transmitter can be accomplished when using
this meter as a field strength meter. Also, comparing antennas can be
accomplished with this meter. It is designed to be used for base stations
or mobile operations and can be permanently installed in the antenna system
without any measurable loss of power.
Specifications
| SWR |
1:1 to 3:1 |
| RF Power |
0- 10 watts |
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0- 100 watts |
| Impedance |
52 ohms |
| Accuracy |
SWR 5% |
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RF Power 10% |
| Meter |
100-250 micro-amp DC |
| Connectors |
S0-239 |
| Size |
120(W)x60(H)x65(D) m/m |
| Weight |
410g |
SWR Function
The SWR Function of the test instrument is probably the most useful test
performed. Testing for the SWR of Standing Wave Ratio provides the
operator of the transmitter a good indication of the condition of his antenna
and antenna lead cable since most antennas are located externally of the
transmitter. In order to get the maximum amount of power radiated from the
antenna, the lead line or coax and the antenna should be matched to the
transmitter. For this meter a 52 ohm match is required which includes most
CB operations that use RG-58U or RG-8U coax. Because a perfect match is
never achieved the amount of mismatch can be measured by measuring the amount of
Standing Waves that exist in the coax or antenna feedline. Measuring the
Standing Waves can be accomplished by sampling the forward "FWD" power
and the reflected "REF" power and comparing them and then expressing
this difference as a ratio of reflected power to forward power. The
following ratios are examples of the amount of power loss for a Standing Wave
Ratio.
| Power Loss |
|
SWR |
| 0% |
= |
1:1 |
| 2% |
= |
1:3:1 |
| 3% |
= |
1:5:1 |
| 6% |
= |
1:7:1 |
| 11% |
= |
2:1 |
| 25% |
= |
3:1 |
| 38% |
= |
4:1 |
| 48% |
= |
5:1 |
| 70% |
= |
10:1 |
A ratio of 1.1:1 to a 2:1 is usually considered satisfactory for most
operations.
Power Meter Function
The power meter function is provided to monitor the condition of the
transmitter by measuring the relative RF power being generated in the
transmitter. This meter will measure up to 100 watts of RF power with 10%
accuracy. This is accomplished by sampling a small amount of RF energy
from the transmission line. There will be no measurable power loss if the
meter is left in the coax as a permanent installation.
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CAUTION: DO NOT TURN THE TRANSMITTER ON WHILE THE ANTENNA AND TEST METER ARE
DISCONNECTED! |
SWR Measurement
- With the meter properly connected and the transmitter off, place the
slide switches on the SWR meter to the "FWD" positions.
- Place the SWR adjustment control on the SWR meter fully counter
clockwise.
- Key the transmitter and adjust the SWR adjustment control for a full
scale deflection to the "SET" mark on the meter.
- While the transmitter is on, place the "FWD-REF" switch to
the "REF" or down position and read the SWR meter. This is the
SWR.
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NOTE: IF THE SWR IS ABOVE 2:1 THE ANTENNA MAY NEED TUNING OR THERE MAY BE A
PROBLEM ON THE ANTENNA OR ANTENNA CABLE. |
- Several antennas provide a means for tuning by either slide adjustment or
a control at the base. For sliding antennas, sliding 1/4" each time
and repeating the SWR measurement steps after each adjustment is usually a good
method. First, moving the antenna inward and watching for an improvement
in the SWR; then, outward if no improvement is noticed. For Citizens Band
operation, tuning your antenna to one of the center channels will usually
provide for the best SWR over the entire band. Use channel 20.
Power Measurement
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CAUTION: DO NOT TURN THE TRANSMITTER ON WHILE THE ANTENNA AND THE TEST METER
ARE DISCONNECTED! |
- Connect the meter in the antenna feed in the same manner as for the SWR measurement.
- For measuring power below 10 watts (standard CB transmitters) place
the switch 10W-100W in the 10W position (up). For measuring power above 10
watts (business band transmitters), use the lower position 100W.
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NOTE: FOR ACCURATE POWER READINGS. THE SWR SHOULD BE NO HIGHER THAN 1.5:1 AND
THE FREQUENCY NO HIGHER THAN 149 MHZ. |
- Turn the transmitter on and read the power.
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CAUTION: ABNORMALLY HIGH READING OR READINGS ABOVE THE RATED POWER OF THE
TRANSMITTER COULD INDICATE A FAULTY ANTENNA SYSTEM. CHECK ALL CONNECTORS
FOR TIGHTNESS OR CORROSION. |
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