Comet CAA 500 Mark II Field Guide

A practical way to find the dip, read the numbers, and make one good antenna adjustment at a time.

The Comet CAA 500 Mark II is a compact antenna analyzer for 1.8 to 500 MHz. It sends a small test signal into the antenna system, measures what comes back, and turns that into SWR, impedance, resonance, and sweep graphs. Think of it as a very patient stethoscope for the antenna system.

Front view of the Comet CAA 500 Mark II antenna analyzer — The CAA 500 Mark II combines a cross-needle meter, color screen, two tuning knobs, and dedicated sweep controls.

The short version

Start with a single-frequency reading when you need an answer at one operating frequency. Use a sweep when you need the whole story across a band. Then make one physical adjustment, repeat the same measurement, and keep the change only if the curve moves in the direction you wanted.

You can Download the complete CAA 500 Mark II PDF guide for the full button-by-button reference, diagrams, examples, and troubleshooting notes.

Before you measure

Disconnect the radio or any transmitter before connecting the analyzer. Never apply transmitter RF to the CAA 500 Mark II. Ground or discharge static from the coax connector before attaching it, and use the correct connector: SO 239 from 1.8 to 300 MHz, or Type N from 300 to 500 MHz.

A 50 ohm dummy load is a useful first check. In Normal mode, a proper 50 ohm load should show SWR of 1.1 or less. If it does not, pause before blaming the antenna.

Normal mode: SWR and impedance at one frequency

Turn the analyzer on, select the general range with BAND, then dial in the target frequency with FREQ. The display and cross-needle meter show SWR and impedance. Below 190 MHz, the LCD also shows resistance, R, and reactance, X.

SWR: how closely the system is matched. Lower is generally better.
Impedance: the total opposition to RF current.
R: the resistive component, which is often near 50 ohms in a 50 ohm system.
X: stored energy from inductive or capacitive behavior. The analyzer shows magnitude, not polarity.

The analyzer measures the system at its connector. A long or lossy feedline can change the impedance presented there and can make the SWR look better than the antenna itself. For feedpoint work, get as close to the antenna as practical; for a station check, measure at the station end on purpose.

Finding resonance

In Normal mode, slowly turn FREQ through the expected operating range while watching SWR. The frequency at the lowest observed SWR is the resonant frequency for the measured system. A dip below your target commonly suggests an element that is electrically long; a dip above your target commonly suggests an element that is short. Make small changes and measure again.

Example SWR curve with the resonance point labeled at the lowest point — The lowest point of an SWR curve is the measured resonance point. The width of the low area shows how forgiving the antenna is across nearby frequencies.

Automatic sweep: the fast band picture

From Normal mode, select the amateur-band segment with BAND and press SWEEP CENTER. The analyzer runs a preset sweep, usually in about 25 seconds, and draws the SWR curve for that segment. Look for the dip, its width, and whether your actual operating frequencies land in the useful low-SWR region. Press GRAPH ON OFF to return to Normal mode.

Manual sweep: the zoom lens

From Normal mode, press GRAPH ON OFF to enter Manual Plot mode.
Use BAND and FREQ to set a center frequency.
Press SWEEP CENTER. The center is held and the sweep limits blink.
Set the desired span with the knobs, then press A P OFF BANDWIDTH to confirm it.
Turn FREQ slowly through the range to draw the trace. The stated minimum resolution is 1 kHz with gradual rotation.

Manual sweep is especially useful for a narrow operating range, a simplex frequency, or any nonstandard frequency plan. Start wide enough to understand the shape, then narrow the span if you need more detail.

Five-color overlays: compare one change at a time

During a manual sweep, press A P OFF BANDWIDTH to cycle the trace color through red, blue, green, purple, and orange. This lets you keep up to five sweeps on screen while you compare a small change in element length, antenna height, surroundings, radial layout, or matching network position.

Keep the same center and span for a fair comparison. If the dip moves toward the target frequency, that is evidence that the adjustment helped. Photograph or note the trace before leaving graph mode, because graph data is not preserved when you change modes.

Power and battery habits

The analyzer runs from six AA alkaline or NiMH cells, or from an external 8 to 16 volt DC source. With NiMH cells installed, the internal charge switch may be set to ON for slow trickle charging. With alkaline cells, the charge switch must remain OFF. The Auto Power Off timer can be set from 0 to 9 minutes by holding A P OFF in Normal mode and turning BAND; 0 disables the timer.

A simple tuning loop

Check the analyzer against a dummy load if the reading seems suspect.
Measure the target frequency in Normal mode.
Use an automatic or manual sweep to see the larger pattern.
Make one small, reversible physical change.
Overlay or repeat the same sweep, then verify the frequencies you actually plan to use.

Sources

This guide is based on the Comet CAA 500 Mark II English instruction manual and the Comet product information page. The SWR curve is an explanatory illustration, not a captured instrument trace.