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SWR Meter/Low Pass FilterSession 4
• SWR Meter Calibration Methods Discussed
• Finish SWR meter• Start the Low Pass Filter Project
SWR Meter Calibration
SWR = [1+x]/[1-x] where x = Sqrt(PR/PF)
• PR is the Forward Power
• PF is the Reverse Power
• We get PR and PF from the SWR meter
SWR Meter Calibration
Forward Calibration Balance Assumed…see manual
Several Methods Possible
1. Make a look up table based on LTSPICE
2. Make a look up table based on precision measurements
3. Use 1 or 2 but create a graph to read SWR
4. Use analog meters like the conventional cross meter type
5. Use 1.5:1 , 2:1 and 3:1 loads….very easy
Read TCA March/April 2012 on SWR/Power Meters,VA3DDN
QST April 2012 on Power Meters..the old basic meter
SWR Meter Calibration
Power Input [W]
VF/VR [V] (LTSPICE)
VE3TLY
VF (Measured) Daiwa meter to set power
10 2.8 2.7
9 2.6
8 2.5
7 2.3
6 2.1
5 1.9 1.8
4 1.7
3 1.4
2 1.1
1 0.71 0.8
0.5 0.41 0.5
0.2 0.2
R4=R3 =0
SWR Meter Calibration
Power Input [W]
VF/VR [V] (LTSPICE)
VE3TLY
VF (Measured) Daiwa meter to set power
10 2.8 2.7
9 2.6
8 2.5
7 2.3
6 2.1
5 1.9 1.8
4 1.7
3 1.4
2 1.1
1 0.71 0.8
0.5 0.41 0.5
0.2 0.2
R4=R3 =0
Example Calculation
VF = 2.7 VR= 0.50
PF = 10 PR = .50
Then x = SQRT(PR/PF)
= 0.22 and
SWR = 1.57
Low Pass Filter14 MHz Application T50-6
INPUT Output
9 Turns 8 Turns
Low Pass Filter14 MHz Application
Second and Third Harmonics Attenuated 45 dB
Low Pass Filter ELSIE
14 MHz ApplicationSecond and Third Harmonics Attenuated > 40 dB
Low Pass Filter Measurements
AIM 4170
Low Pass Filter Measurements
HP Analyzer VE3ZRK
Simulation
1. Put the supplied filter file into a folder on your computer
2. The file name is VE3KLCauerLowPass14mHzappVersion2.LCT
3. Open up the Elsie Program
4. Click Retrieve Old Design then open the file above
5. Click Schematic if not opened to start the process
6. Click Plot
7. Now experiment with the filter plot options and
other windows
Construction
1. Build each resonator and test with AIM 4170
Put capacitors close to the coils. See my models
Leave lots of wire on inductors as before
Rewind coils if necessary: 9 turns and 8 turns
# 26 Gauge wire. I have lots of wire and toroids
2. Now label the input/output ports of the circuit board
with supplied label
3. Wire the series parts first, then solder the
parallel capacitors
4. Measure the SWR with the AIM meter
Summary• Can improve SWR meter by using matched diodes
and transformers. Use 1% resistors.
Good example of Ferrites
• Low Pass Filter good for filtering square waves
Good example of Powdered Iron (High Q)