J-INDEX is an index value for measuring true MW reception conditions, kind of a "NASDAQ index for MW". Other common indices (such as A / K / solar flux and more) just describe space weather related geomagnetic characteristics but do not give a real MW-reception index value.
JIX is scaled from 1 to 100. By default, JIX is collected from the "overseas frequencies" based on the user's location. JAGUAR keeps track of signal levels on the first 100 MW frequencies (the overlapping NA/EU frequencies are excluded) and creates the averaged value which is named as the J-INDEX. The JIX values are being automatically calculated when the hardware is plugged in, and the values will be saved to the YAS LOG file ("DAY.YAS") at one-minute intervals.
To be exact, JAGUAR calculates and collects two separate JIX values: one for MW10 frequencies and second for MW9 frequencies. If you change the MW frequency stepping, the JIX shown changes accordingly.
JIX offers an excellent tool for finding interesting spots when studying the recorded files. In addition, JIX can be used for comparing antennas and even QTHs (however, the effect of using an external preamplifier must be taken into account when comparing signal levels in two different QTHs).
Additionally, JAGUAR collects hourly values for the MW10 and MW9 JIX to CONDX.LOG. This log is used on the CONDX display (more details in the CONDX help) to compare classical solar index values (A / K / Kyoto / etc) with real trans-oceanic reception results (JIX CURVE). These files are saved in the daily recording folders.
In addition to STATUSBAR and CONDX, the JIX values are shown as red curves on the HISTORY and YAS LOG displays. When reviewing the JIX CURVE, you should look for the curve peaks (the sharper, the better!). Even a small peak in the curve can indicate a good spot for DX. Also, you should look for the times when the JIX value is rising/falling rapidly. Experience has shown that those times often offer the most interesting reception periods, e.g. perhaps dominants may have not faded in yet or may already have faded out, and the dial can be full of surprises. While in a DXpedition, we often monitor these rapid changes as a trigger to be especially alert.
The JIX can also be used to automatically start recording when a user-defined threshold is reached (see AUTOREC in MESTOR). Even though today's megatrend in MW DXing is to record everything overnight and use various analysis tools to see/hear the results, many users still prefer to record only the TOH times. In this case, AUTOREC can be combined with scheduled TOH recordings. In this way, all the good out-of-TOH openings will be recorded automatically. Or why not record only the "good openings"?
JIX is controlled and handled automatically by JAGUAR; you just have to be aware of this feature.