Many readers still get this wrong!

(c) Pxhere

Last week, I posted a poll on LinkedIn where I asked:

On a MOTOTRBO Capacity Max system, which of the following hardware configurations is going to give you more range under the same conditions?

1. SLR8000 at 100W with DP4801e.

2. SLR5500 at 50W with DP4801e.

3. Both will give you the same.

Note: "same conditions" means same location; antenna frequency etc. etc. 

The correct answer is 3: Both configurations will give you the same range. Why?

The general misconception is that more TX power on on the repeater side will provide more range. While is is true if the radios were only receiving, it is not the case when you consider both the talk-in and talk-out paths.

If this were a IP Site Connect or Multisite Capacity Plus system, a portable radio would continue to receive most calls but if the radio user is too far out, they would not be able to talk back since the <5W ERP from the portable would not be enough to reach the repeater. So even in this case, having more power will only help if communications is receive only (e.g. paging).

Capacity Max (and any DMR Tier 3 system for that matter) requires the radio to register in a site. When powering on, the radio will go into a hunting procedure whereby it will search for a control channel on specific channels or in a frequency range. Once a control channel, with a certain minimum signal strength and bit error rate is found, the radio will attempt to register. 

If the registration fails, the radio will continue to search for another control channel until it finds one that meets the signal strength and successful registration criteria.

Once registered on the system, the radio will monitor the control channel for calls and other commands. One of the commands the system will periodically send out is a Vote Now. This allows the radios to leave the current control channel and measure the signal strength of the adjacent sites' control channels. Based on this sample, the radio will apply a ranking algorithm that will allow it to move to another site if the signal strength on the current control channel becomes too weak.

If the radio user is moving and the current control channel signal becomes too weak, the radio will roam. Roaming in capacity max is a little different in that the radio will perform a simplified registration on the new site. If this fails, it will try the next site down in its list.

SLR8000 repeater

If one had to compare a 100W SLR8000 + DM4600e 45W (non-CE) to a 50W SLR5500 + DM4600e 25W, there would be a noticeable difference since there is almost a 3dBW difference at both ends.

My point being, having a 100W repeater is only useful if you are mostly interested in receive-only coverage or if high-power mobiles are used. 100W will get into dead spots better but that's no use if the users radio wont register or they cant respond to incoming calls.