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)