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The SFR (for the reason you stated) is one of various radio applications digital allows.  The lowest cost hi-power commercial SFR unit I posted elsewhere is $400 (plus $120 shipping):




This Hytera portable also has this built-in:




I can only imagine how handy the portable would be for search and rescue, etc. - just duct-tape it to a tree on a high hill in SFR mode (with an extended battery) and you are done.      


Other division duplex (TDD) products would include low power, 10-100 mW "hotspot" devices for under $150 - these are already developed for DMR in amateur.   They could then be networked..with full-duplex repeaters if needed. 



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What would intrigues me about DMR are some of the radios that will function in SFR, single frequency repeater, mode. Of course you have to find one that works.


Anyway the attraction is no requirement for using any kind of "cavity" filters which would be necessary on a more traditional in-band system. This means almost anybody could setup a repeater with far less technical expertise required and cost for a decent set of BPBR filters. So until the FCC changes the rules we won't have DMR on GMRS. I do expect that to happen sooner or later, likely much later.   


Yes, to a point.  BUT you loose the TDMA aspect of it. Meaning that you can only have a single talk path when operating like this and this mode will require everything to be brand specific.  Motorola will work with Motorola, Kenwood with Kenwood. 

Now mind you, I am a commercial radio tech.  But I don't see how not needing a duplexer is that big of a deal on a fixed repeater.  Due to the fact we are limited to 50 watts of power, the small mobile duplexers that are typically rated for 40 watts would do a fine job and they are inexpensive on the used market.  Yes, there is the tuning aspect, but that's not a big deal.



I don’t believe using a radio in SFR mode requires all radios to be from the same manufacturer. They simply would be required to adhere to the tier 1 and 2 DMR standard. Only the single radio functioning in the SFR mode would be communing with normal DMR radios.


With the current rules a conventional analog in-band repeater requires two distinct frequencies, one in the 462.xxx range and the other in the 467.xxx range. So you have two frequencies used to support only one voice channel.


Using a SFR one could operate two repeaters, one on a 462.xxx frequency and the other on a 467.xxx frequency. You now have doubled the number of repeaters without consuming additional spectrum.


On simplex a number of radios can use what is referred to a Dual Slot Direct Mode. Apparently there are radios that will sync to each other using only one time slot without the requirements of a repeater to supply the time slot sync. What this does allows two such radios to use a single simplex frequency using just one of the two time slots. Another two radios on the same frequency could use the other time slot thus doubling the number of effective voice channels, again without consuming addition spectrum.






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