SWR-121 HF Antenna Analyst Operating Manual Adjustments

Battery Replacement Turn the instrument off before replacing batteries. The two screws under the rubber foot allow access to the battery compartment. See the INTERNAL ACCESS

section of this chapter for more information. Be careful to insert the batteries according to the markings on the inside of the case bottom to avoid damage.

Calibration Although calibration will not normally be required unless components have been replaced, the procedure is given for reference. Calibration must be performed with fresh batteries and external power disconnected. See the PARTS PICTORIAL for lead connections and parts locations.

TIMEBASE: Connect a frequency counter to the antenna connector. Turn the instrument on and adjust trimmer capacitor C39 for a reading of 10 MHz. Alternately, you can set a receiver to WWV or some other station of known accuracy, set the SWR Analyzer to the same frequency (with dot width set to 0), and adjust C39 for zero-beat.

BRIDGE AMPLIFIER GAIN: Press and hold the ENTER button while turning the instrument on. After several self-tests are completed, an F and an R will appear in the display. Adjust R51 and R50, respectively, so that the F and R are vertically aligned at the 'ALIGN' arrow near the right side of the display with the antenna connector open (no load connected). These letters indicate the Forward and Reflected voltages from the SWR bridge. The right side of the display represents 5 Volts (full- scale); the left side represents 0 Volts. (If adjustments are made with old batteries, erroneous SWR measurements may result when they are replaced.)


1) If the Calibration mode is entered while the instrument is powered from an external

source, the letters F and R will appear near the center of the display. As long as the letters are vertically aligned within a pixel or two, accuracy will be maintained.


then on to set a center frequency of 10 MHz and 0 width. Connect a voltmeter between ground and pin 6 of U8. Adjust C25 for a reading of 7.0 Volts.

INJECTION OSCILLATOR: Connect an oscilloscope to the antenna connector. Adjust C31 for a peak, using a non-metalic tool. If the waveform shows any flat-topping, adjust C31 away from peak slightly until the flat-topping is eliminated. (Adjusting too far off of the peak may result in the oscillator stopping.)

VIEWING ANGLE: While viewing the display from the angle normally used, adjust internal control R4 until the background dots disappear.