NN0M

For DV to be appealing it needs to be easy to implement, offer advantages over analog, and be inexpensive.  

So which DV system does one choose?  

DV is a digital mode. The underlying issue with all digital modes is that the A/D and D/A conversions have to
implimented either:
1. on a computer which is seperate from the radio, or else 
2. they have to be an embedded system within the radio. 
So which of these 2 models is the most practical to impliment for your applications and which implimentation will
meet the criterions. The answer to this question will influence which DV options are viable for you in a profound
manner. 

If you want portable radios; an embedded implimentation will be your go-to. 

If you need to communicate information over great distances; then the external computer/sound-card
implimentation will probably your starting point. 

Many of the embedded DV systems which Hams are experimenting with or adopting are limited with regard to off-
the-shelf radios to either the 2 meter VHF band and/or the 440 UHF band.  Not being able to use these DV
implementations on HF is a substantial barrier to becoming adopted and used by a substantial number of Hams. 

DMR relies on time-slicing and requires a hardware implementation. Few radios with the exception of those that
operate only on the 2 meter VHF band or the 440 UHF band support DMR.  So except for these 2 bands it is for the
moment not very appealing to experiment with. I got an MD-380 and experimented with it; and was underwhelmed.
DMR linking is for now lacking any substantial established RF backbone and relies on commercial internet providers;
it is a nifty toy but not currently robust and reliable enough to be suitable for EComm situations. 

I see mobile amps advertised which claim to be compatible with DMR.  I tend to be wary of these claims given the
short length of the time slices.  So for this reson I am wary of even suggesting that an external amp could give an HT
some help if used in a mobile environment. With DMR I feel that if you need more power you probably need a
different radio. 

P25 (Project-25) commercially available radios like DMR also are too rare to be of interest to most Hams except on the
VHF and UHF bands.  

D-Star uses a codec which requires a license fee to experiment with much less use widely on a variety of bands. So the
$200 price point for a DV-Dongle; which is the lowest entry price-point for people that want to experiment with this
mode. $200 for an experiment will be off-putting to many Hams. 

I have not explored C4FM nor the proprietary System Fusion implementation of it. So I can not offer an informed
opinion about its strengths and weaknesses. It is my perception that C4FM is also pretty much only implemented on
2 meters and 440. I know that the Kenwood repeaters are limited to these bands. I am unaware of any radios which
support System Fusion on 6 meter VHF. 

FreeDV has the right price-point to make it worth experimenting with. It is implemented on a computer which
interfaces to a sound card. So it can be tested and utilized on any band with any radio which can be interfaced to the
sound card.  As Ham's; for majority of us that means it can be used on any radio we own. The exception to this is
vintage radios for which the original connectors are hard to get; In EComm situations using modern radios often
makes more sense because those radios tend to be much lighter in weight and they tend to require less power to
operate. Modern radios which use less power can operate longer from a battery which has a given number number of
amp hours.  Running off of a generator with a modern and more energy efficient transceiver can mean that you can
use a smaller and presumably lighter weight generator to keep you radio operating. 

- NN0M