Electricity Cost Per Minute on DMR-MARC Network

Electricity Cost Per Minute on DMR-MARC Network

[MOTOTRBO] Cost projection on DMR based on breadth of the TG site coverage.

I got bored, took the local 'pyramid' of talk group repeater count spread, applied the electrical costs for a repeater at 45W transmit, and multiplied that out over increasing talkgroup repeater counts.

Kind of interesting, basically 20min of tx time on North America roughs out at $4 in electricity consumption alone.

I did this as a tool to show people the significance of minimizing the reach of the talk group used to make a contact.

Intro - Why?
Electricity Cost Per Minute While Transmitting on the DMR-MARC/NEDECN Network - de KC2RGW 11/15/2015 rev.2.1

So out of boredom I was wondering what it actually costs in electricity when you multiply the effect of a user transmitting on the DMR-MARC network (NEDECN biased). I’m doing this as an illustrative tool for people to think about how they use the network from a localization and least number of repeaters impact to make their contacts.

This isn’t meant as any sort of environmental impact statement or even one that is very specific to DMR technology. It is however specific to DMR in the way a single user has power and leverage over a vast network of resources. Site per site, if anything, DMR should be more efficient than analog due to efficiency of throughput with TDMA and the lower duty cycle of the mode.


Single repeater power consumption:
  • A Motorola 8400 repeater runs at roughly 120V AC @ 4A on transmit
  • Taken from Motorola’s data sheet
  • This works out to 480W consumption.
  • So a revision here...at 45W output we had a site owner measure actual consumption at 144W with a Kill-A-Watt meter on the source. Figures have been dropped to reflect this.
  • I used $0.12 kW/hr as a rough cost for power
  • This is lower than it is locally, but national avg is $0.10 kW/hr
  • I adjusted to $0.10 kW/hr in the revision as well but remember, some areas are over $0.15 kW/hr
  • The cost per hour in transmit mode is about $0.0144 <- revised as well
  • This works out to $0.00024/minute for a single repeater while it is in transmit mode.

That’s pretty cheap….right?

The Math - Let’s see how much this will cost us.

Talk Group Selected
Number of Repeaters Engaged
Cost For 3min Transmission
20min total repeater time for conversation.
Local TG9
TAC / UA channels
VT Statewide
ME Statewide
MA Statewide
SNE/Region South
NH Statewide
NNE Region North
New England Wide
North America
WW English 
WW Call
WW potential total 


The big one to notice in this chart is the difference between two people talking, using all of North America at a cost of $4.00 vs simply switching to a TAC or a UA which would be $0.03 for the same conversation.
This is all based on napkin math and misses a lot of nuances, regional power rates, the cost of the network connections between the sites (some sites are using cell data, some are paying for dedicated internet etc) and likely other smaller things. 
This doesn’t have the cost of the repeaters, the antennas, the feed line, and any other site charges and of course, this has no metric for the time and effort the site maintainers put in to keep these sites running. I believe these figures to be quite conservative.
My point isn’t some sort of environmental impact statement, it’s purely using a monetary metric for awareness of the impact a single user can have. It becomes kind of silly when I hear a conversation about a local issue that drones on and runs up a $4 tab on North America or other wide area talkgroups, when it could have been completed in many cases on TG9/local or on a UA/TAC between the two parties.
The awesome part is, I do not frequently hear this issue with our region in New England, and that is due simply because we are all helping the new users (hell, I am a new user myself) understand how this network works and how best to apply it as a resource.
It takes patience and active efforts to continue to educate people on how the DMR networks function. Growth is extremely fast right now so it will be important to keep up the good work here to keep the networks capable and healthy.
Please feel free to pass this link around or to use this doc in presentations. I would ask that you just leave my call sign in and the date at the top when you attribute the source for context.
-- 73 de KC2RGW

Here's the document in full.


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