Vectronics SWR-584B - Manual (Page 17)

SWR-584B Instruction Manual HF/VHF SWR Analyzer
17
as 75 feet, and the transmission line is a typical RG-8 solid dielectric cable with a velocity factor of 0.66, the
distance is 75 x .66 = 49.5 feet.
There is one limit to this mode, the mistermination or fault must not be periodically frequency sensitive. For
example, this mode will find the distance to a remote selective circuit (like a standard link coupled antenna tuner)
that appears as a short or open at all frequencies but one. It will not reliably find the distance to a low pass filter
unless the test frequency is above the filter stop-band. This mode will work properly if the mistermination is a
nearly pure resistance, but will not work reliably if the load is a mostly pure reactance.
To confirm reliability, make two or more groups of measurements on different starting frequencies at least one
octave apart. If measured distances agree, they are almost certainly very reliable. The more base frequencies
used to confirm distance, the more assurance we have that distances are correct.
To measure fault distance:
1.) Select a frequency where the Impedance meter is at the lowest deflection possible and where minimum
reactance displayed on the SWR-584B LCD, or where the reactance crosses zero. The reactance zero-
crossing frequency is the frequency where reactance rises when the SWR-584B is adjusted either higher or
lower in frequency.
2.) Press the “GATE” button. The blinking “1st” will change to a blinking “2nd”.
3.) Tune the analyzer higher or lower in frequency until the Impedance meter reads the very next lowest
impedance point on the meter, and reactance displayed on the LCD crosses zero or is at the lowest possible
again. A non-zero minimum of a few ohms is acceptable.
4.) Press the “GATE” button again, and the display will indicate distance in feet.
Multiply the distance in feet by the velocity factor of the cable. The result is the physical distance in feet.
Example: The SWR-584B indicates 13 feet, and the cable is a standard foam cable with a velocity factor of
0.80. 13 multiplied by .80 is 10.5 feet. The fault is about 16 feet away.
5.6 Resonance Mode