A few years ago I programmed a Uniden 436 and a GRE PSR-800 with the exactly the same with 3 seperate trunk systems. Some sites were 10 freq's and the other had 20 or so. I noticed the Uniden was sweeping through every frequency on a tower site while my GRE responded to the first active TG from another site. Is this the way Uniden scanners are made to scan since the 396T was first released in this format?
No. There's a couple of steps to the process.
First, Uniden uses Location Control to decide which site(s) are in range and scannable. If you disable Location Control, have your location set incorrectly, or have site location data set incorrectly, the scanner will waste time trying to scan sites that are not actually in range.
But if the site is in range, the scanner will scan through the site frequencies until it finds the control channel. You can streamline this by putting the current control channel at the beginning of the list of frequencies for the site. Once the scanner finds the control channel, it will not look at other programmed site frequencies.
When the scanner finds the control channel, it will spend 1-2 seconds parsing it for active transmissions. If there is one, the scanner will look up the Talkgroup ID to see if its Service Type is enabled, and will also look up the Department for the Talkgroup to see if you are in the Department's service area as defined by your Location Control settings. If not, the scanner will move on and skip the transmission. But if all the criteria are met, the scanner will switch to the voice channel specified by the control channel. For P25 systems, the voice channel frequency doesn't have to be programmed, the scanner gets it from the control channel.
The most common error is not having all of the appropriate Service Types turned on, which causes the scanner to ignore traffic it can easily receive, but thinks (mistakenly) that you don't want to hear.
The next most common error is having Location Control misconfigured, particularly having it turned OFF for large multi-site trunked systems. This forces the scanner to waste a lot of time scanning sites it cannot hear, which results in missing traffic. A lesser (but common even in the RR database) error is not having the control channel as the first frequency listed for a site. This isn't a critical error, but slows the scanner down a little by forcing it to check frequencies other than the control channel freq before finding the control channel.