Cross-Site Pollution


When moving a signal role receiver from one site's control channel to a different site's control channel, there is a risk of data from the new site being applied to the former site. The result is incorrect, inaccurate data. To recover from this, you can manually delete objects (channels, groups, users, neighbor sites) that don't belong. You can also use the "take me back" feature found on the Archive tab to roll-back your data to a previous, un-polluted state.

Having a back-up of your data is a good idea. It's also best to avoid the circumstances that result in polluted trunking data.


The Discover option is a check box in the Decode section of the receiver window. Turning this on allows the signal role receiver to accept any signal - among those protocols also checked in the Decode section - for decoding. In other words, you tune the receiver to a signal and let the decoder discover what's there.

In this mode, the decoder makes conservative assumptions about the signal received. When a Motorola signal is acquired, the site number defaults to zero until an actual site number is observed in the control channel stream. This is called an ad-hoc site. When an EDACS signal is acquired, the program creates a brand new site and system. It waits until it has the site number, control channel number, and control channel frequency before attempting to match these to a previously logged site. The temporary system is referred to as a Limbo system. If a match is found, the Limbo system is discarded. If a signal is lost - the whole discovery process starts over. In the case of EDACS, this can result in multiple Limbo systems. The decoder has no way of knowing whether the previous Limbo system and re-acquired system are the same. In additional to Adhoc sites and Limbo systems, decoding while Discover is turned on has a risk of cross-site pollution - if and when you move the receiver to a different control channel. There's no risk as long as the receiver stays put.


Once the receiver has acquired a signal, turn the Discover option off to reduce the risk of cross-site pollution.


With Discover turned off, you can also turn on the Chase option - which allows Both, Inline, and Realtek based receivers to follow the control channel when it moves. Chase isn't an option for manually tuned discriminator tapped receivers that do not support computer control. Chase is also not an option for some Inline models that don't accept computer control. For these receivers, you can program the receiver to follow the control channels of a site for you. Details vary by model.

Note that Chase and Discover are incompatible features. You can have one or the other - or neither - but not both. If you select Chase while Discover is turned on, Discover will be turned off. Likewise, if you turn-on Discover, Chase will be turned off.


The dwell setting tells the program how long to wait before moving on to the next control channel when Chase is turned on. A value of 1000 milliseconds works well for most receivers and signal conditions. If you are monitoring a distant site that is prone to fade, you may want to increase this value. The worst-case time to find the control channel that has moved is at most "N" - 1 dwell times where "N" is the number of control channels. With a 1000 millisecond dwell time on a Motorola system with four control channels, it can take 3000 milliseconds (3 seconds) to recover. That assumes good reception.

Chase and Dwell

Pick Site

The safest way to switch a running signal role receiver from one site to another is to do so through the receiver window. You can type in a new control channel frequency. Doing so implicitly turns on Discover mode. If you're like me, you have trouble remembering all those frequencies. An easier way to switch sites is with the Pick Site dialog. It's available as a button on the receiver window toolbar. You'll see three combo boxes - Systems, Sites, and Channels. Below that are some check boxes. Some of these checkboxes match check boxes in the Decode section of the receiver. The Systems combo box lists all named systems that match the checked protocols. Unnamed systems are omitted (be sure to name your systems). The Sites combo box lists all sites for the selected system. The Channels combo box lists channels for the selected site. In some cases, you may have a site with a hidden control channel. This is usually one of the voice channels that - for whatever reason - hasn't been observed as a control channel. Check the "Include Voice Channels" box to include the voice channels in the Channels combo box. Otherwise, only known control channels appear. Select a control channel for the desired site. The receiver will be tuned to that channel. If you don't see any data right away, try the next channel in the list. Once you've found the active control channel, click OK. In picking a site in this manner, Discover mode is - by default - turned off.

Pick Site Dialog

© Copyright 2014 Rick Parrish