ab cd
Senior Member
SIMULATION RESULTS
Gain = 3.7 dBi
SWR = 3.1
Impedance = 155 - j 8.18 ohms
HIGH IMPEDANCE/SWR - WILL NOT GIVE GOOD RESULTS WITHOUT IMPEDANCE MATCHING
IMPEDANCE MATCHING BY "TRANSMISSION LINE+CAPACITOR" TECHNIQUE
Using Smith Chart:
Capacitor to be inserted = 3.8 pF (4 pF will do)
Coax length (from antenna) where Capacitor should be inserted = n x λ/2 + 80.8mm Coax of VF=0.85,
where n is any integer.
ACTUAL IMPLEMENTATION
This is a two step SWR improvement process.
STEP (1): Trim RG6 feed coax at the pigtail till value of R becomes close to 50 ohms.
STEP (2): Add a capacitor in series with core wire of coax to nullify +X component of impedance. Location of capacitor: between pigtail and filter.
By doing the STEP (1) ONLY, impedance changes from 155-j8.2 (TP1 on Smith Chart) to 50+j38.3 (TP2 on Smith Chart). This results in changing SWR from 3.1 to 2.1, which gives a big improvement in performance.
Doing STEP (2) after doing STEP (1) results in impedance becoming 50+j0, and SWR=1, a perfect match.
Note: Unfortunately I have miss-calibrated my antenna analyzer using a 75 ohm resistor. Now it is not resetting to factory calibration of 50 ohms. I have ordered a 50 ohm dummy load resistor. Waiting for delivery to re-calibrate the Analyzer with 50 ohms load. I therefore could not actually do the impedance matching. Following only show the steps I will do when my Analyzer is re-calibrated.
Gain = 3.7 dBi
SWR = 3.1
Impedance = 155 - j 8.18 ohms
HIGH IMPEDANCE/SWR - WILL NOT GIVE GOOD RESULTS WITHOUT IMPEDANCE MATCHING
IMPEDANCE MATCHING BY "TRANSMISSION LINE+CAPACITOR" TECHNIQUE
Using Smith Chart:
Capacitor to be inserted = 3.8 pF (4 pF will do)
Coax length (from antenna) where Capacitor should be inserted = n x λ/2 + 80.8mm Coax of VF=0.85,
where n is any integer.
ACTUAL IMPLEMENTATION
This is a two step SWR improvement process.
STEP (1): Trim RG6 feed coax at the pigtail till value of R becomes close to 50 ohms.
STEP (2): Add a capacitor in series with core wire of coax to nullify +X component of impedance. Location of capacitor: between pigtail and filter.
By doing the STEP (1) ONLY, impedance changes from 155-j8.2 (TP1 on Smith Chart) to 50+j38.3 (TP2 on Smith Chart). This results in changing SWR from 3.1 to 2.1, which gives a big improvement in performance.
Doing STEP (2) after doing STEP (1) results in impedance becoming 50+j0, and SWR=1, a perfect match.
Note: Unfortunately I have miss-calibrated my antenna analyzer using a 75 ohm resistor. Now it is not resetting to factory calibration of 50 ohms. I have ordered a 50 ohm dummy load resistor. Waiting for delivery to re-calibrate the Analyzer with 50 ohms load. I therefore could not actually do the impedance matching. Following only show the steps I will do when my Analyzer is re-calibrated.
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