Originally posted by joni1101
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Theoretically horizontal radials have 32 ohms, 45 degree slanting have about 50 ohms and vertical (i.e. a dipole) have 75 ohms.
Practically for ADS-B, I compared message rate for horizontal and 45 degree slanting radials, and noticed only slight increase in adsb message rate with slanting radial. Please see this post:
Why Antennas Have Ground Plane?
Please note that the instrument I have used measures only VSWR/R/X/Reflection S11.
It does NOT measure following important parameters:
1) Antenna Gain
2) Antenna Directivity/Radiation curve
3) Common mode/unbalanced currents in feed coax
The purpose of this instrument is to check:
(1) At what frequency antenna is tuned. The tuned frequency is where the SWR-Frequency curve is at minimum. If it is tuned at lower than design frequency, trim the whip, if tuned at higher frequency, add a piece to whip.
(2) How much is VSWR. If measured VSWR is greater than 1.5, than impedance matching devices should be used. Once the VSWR is below 1.5, its actual value does not matter, then it is the Gain and Directivity which really make difference.
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