Spot Source Filtering vs. Pre-filtering vs. Spot Database Display filtering
There are three ways to filter the SpotCollector's display of information about active stations. This article compares and contrasts them.
Filtering the Spot Database Display
As described here, SpotCollector harvests information from incoming spots to maintain a database of active stations, with each entry in the database collecting information about a particular station operating in a particular mode near a particular frequency. The benefits of this approach are
- All the information about an active station is accessible from one entry: when it was first spotted, when it was last spotted, world regions from which it was spotted, distance from your QTH to the closest spotting station to your QTH, smallest and largest SNR reported
Computationally expensive actions like propagation prediction can be automatically initiated when a station is first spotted, and hourly thereafter
Multiple views of information from the Spot Database can be simultaneously generated: in a table, on a world map, on a bandspread, on a panadaptor, or in a chart optimized to reveal propagation openings.
Each view can be independently filtered, meaning that a user-specified subset of active stations is displayed. General filters -- by band, by mode, by continent, by spotting station, location, by participation in eQSL or LoTW, by age - enable quick selection via checkboxes. Because SpotCollector has access to the DXing objectives you've specified in DXKeeper and the Realtime Award Tracking tables that DXKeeper maintains for the DXCC, IOTA, Marathon, VUCC, WAS, WAZ, and WPX award families, SpotCollector can provide a Need filter, which shows only active stations with whom a confirmed QSO would advance your progress towards the awards you are pursuing.
More precise filters can be specified using Structured Query Language (SQL). If you're trying to work South Korea on 30m, for example, then filtering with the SQL expression (Band = '30m') and (DXCCPrefix='HL') would identify both the operating patterns of Korean stations QRV on 30m, and propagation openings that you can exploit to work them.
- While views of the Spot Database may be filtered, information from incoming spots continues to be inserted into the Spot Database, whether or not it conforms to any of the current filters. No information is lost.
However, maintaining a Spot Database is expensive in terms of computational and memory resources. With spot sources that can deliver tens of spots per second, the Spot Database can grow large. When a spot arrives for callsign C in mode M on frequency F, the Spot Database must be searched for an existing entry for C in M near F. If found, that existing entry must be updated with information from the spot; if not found, a new entry must be created and populated with information from the spot. SpotCollector provides functionality that enables users to manage this computational and memory load, but exploiting this functionality requires effort by the user.
Pre-filtering the Spot Database Display
DXers living in regions with large ham populations - like North America, for example - quickly work stations in their region's countries on each band and mode of interest. Subsequent spots of home region stations are thus of no interest, unless you enjoy working friends and acquaintances when they are spotted. Most DXers only operate on a subset of the available ham bands, and in a subset of the available modes; spots of stations on other bands or in other modes are also of no interest. To avoid wasting resources on spots of stations that are not of interest, SpotCollector can be configured to pre-filter such spots, avoiding the expensive search of the Spot Database.
Unlike filtering views of the Spot Database, pre-filtering discards information. Information from a pre-filtered spot is discarded; the only way to recover this information is to disable pre-filtering and then use a Spot Source window to manually issue an appropriate SH/DX command to its connected cluster.
Filtering Spot Sources
Some DX Clusters can be configured to withhold spots from specific countries, band, or modes. This approach slightly reduces the computational load generated by SpotCollector compared to pre-filtering. It requires the user to manually issue appropriate commands to the cluster. Like pre-filtering, spot source filtering discards information.
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