Better Scan using Rx Groups

TRBO radios have a limit of 15 channels (modes) in each scan list.  There is also a limit of 15 group call (Talkgroup) ID's per Rx group list.  While Rx Groups provide instant response to talkgroup activity, scan uses the old slower style of channel sampling known to us all from the old analog days.   This old fashion approach increase the potential to miss the beginning of a transmission, especially when you have a large group of 15 modes entered in your scan list.  This page will show you how to minimize those delays while increasing your ability to monitor 30, 60 or more talkgroups efficiently.

While Rx groups are very efficient and the preferred method to listen to multiple talkgroups, they will not listen across timeslots.  But scan does traverse the timeslots, so both scan and Rx Groups can be integrated specifically to maximize speed, efficiency and increase the maximum number of talkgroups that can be monitored.  Our thanks to Greg, N6LDJ, for suggesting the idea to us at DCI.

This methods real value is for use on networks that use many talkgroups (DCI).  Analog modes and other digital frequencies can be included though it reduces the scan speed somewhat as it relies on channel sampling.  Our USA codplug has a zone with the associated Modes, Rx Groups and a Scan list that illustrates the instructions listed below and we would suggest that it be used as your sample or to  refer to our codeplug as you read below.

1)  Go to Scan Lists and create 1 new scan list called "z RX & Scan".  Uncheck Talkback so you don't Tx on the non-selected mode inadvertently.  Leave the scan list blank for now.

Note: the "z and a space" before RX & Scan will enable sorting this scan list to the bottom of the scan list if you so choose.

2)  Go into your Rx Groups and create a 4 new groups labeled "zDCI1 TS1a & Scan",  "zDCI1 TS1b & Scan",  "zDCI1 TS2a & Scan" and lastly, "zDCI1 TS2b & Scan".

Note: the "z" before "DCI1 TS1a & Scan" and the other 3 Rx Groups will enable sorting this scan list to the bottom of the scan list if you so choose.   You may use any talkgroup, DCI 1 was chosen for the USA codeplug.  It doesn't matter as Tx is unimportant.

Populate all your more important TS1 talkgroups into the "zDCI1 TS1a & Scan" Rx Group.  Then populate the next most important TS1 talkgroups into "zDCI1 TS1b & Scan".  Repeat for the TS 2 talkgroup into the 3rd and 4th Rx Groups.  If you need more talkgroups in excess of the 60 supported here, simply create a TS1c and TS2c set of Rx Groups and fill them with you additional talkgroups.  You can also put your highest priority talkgroups into each of the Rx Groups lists so that they are sampled more frequently as the radio is scanning.

3)  Create a new zone in your codeplug called "z Rx & Scan".  It is optional to create a new zone but it's prudent not to muck in a working zone until you know you know you have this all working correctly.  You will not use this zone per se but the Rx Groups associated with the modes in these zone are the key to this method.

4)  Create 4 modes in this zone labeled: "DCI1 TS1a & Scan", "DCI1 TS1b & Scan", "DCI1 TS2a & Scan" and "DCI1 TS2b & Scan".  Use your home or main repeater info but make sure that all modes use scan list: "z Rx & Scan".  In each of the 4 modes, place the matching Rx Group list in the "group list" field on the left side in CPS under RX.  Check the auto-scan box though not critical.  We suggest you make this a "RX only" as you really should never need to transmit or really never even select this zone (trust us on this for now) so any TX contact is unimportant.  Remember, the purpose of this effort is to listen, not necessarily transmit.  That comes later.

5)  Go back to your Scan List and now populate it with the 4 modes created in your "z Rx and Scan" zone.  If you have a preference of which TS of the 2 modes, then set the priority also in the scan list.  We suggest you set you set your first and second modes as Priority 1 and 2 if you have any priority talkgroup preference, but it is optional.

6)  Now you can make use of all of the above work...by simply creating 1 mode in any zone of your choice.  Even a new mode is optional but what you should do is place the "z Rx and Scan" scan list into this new mode or existing mode.  Make that mode an auto-scan mode as this is the key to listening to 30 plus talkgroups.  Label your existing mode with extra characters such as "AllScan" or "AllRx" at the end of the label so you know this is the super duper auto-scan listener mode.

That's it...now you can, from any zone, listen to everything without even hitting a scan button.  30, 60 or 90 talk groups is just a click of the selector (HT) away.  If you see your repeater is active but don't hear anything, just select your mode that has this scan list in it and it will auto scan.


Optional:  if you wish to create a priority for the RX groups then you can further create more Rx Groups based on priority and timeslot.  But as you add more modes to your scan list you degrade the speed of the scan due to it's channel sampling.  Scanning only 2 modes has essentially eliminated any clipping of the beginning of a transmission so 3 or 4 modes still will pack much benefit.

Optional:  If you wish to further refine you list of talkgroups to a smaller subset, then simply create more Rx groups and only add the more important talkgroups.  Create another scan list for this subset of mode(s).  Make the mode label descriptive of it's purpose so you can easily keep track as you spin the mode selector.

Cons:  If you use nuisance delete, you will lock out up to 15 talkgroups in one fell swoop unlike just a single mode which is normally done when using nuisance delete.


Let use know how you fair on this rather unusual implementation of Scan using RX groups.

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Revised: 09/19/2014 05:13

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