Both GMSK modem and DMK URI provide a shaped and limited waveform
that can be directly FM'ed at what is easily set to 1.8khz +/-
typical... ( this is what the Icom stations use) the waveform is cleaner
out of my station than the Icom D-Star radio keying it and filtering is
better out of the station. Excessive deviation really annoys Icom's
D-Star radios so not much slop is tolerated. Deviation above ~2k is a
problem as the receiving radios start having issues.
We have no currently mandated amateur initiative for 12k5 (11k0f3e) let
alone 6k25 (6K00F3E/2D/2E) so I am not losing a lot of sleep with my
12k5/25k0 switchable receiver running in 25k0 mode...My repeater council
authorized spectrum allocation is a 25k0 spec channel.. The GMSK modems
and URI's do not seem to care as of now.. so I am planning on dealing
with narrowband RX hardware down the road...Hardware narrowband filters
are much more problematical in flatness and ringing... etc...
What we really need is DSP based second IF's.. I suspect with HPSDR
and other similar projects.. in the not too distant future...we could
and will come up with an 11.2 mhz (or whatever is needed for a
particular station... ) DSP based second IF with direct sampling
hardware... just like, for one, GE ( Harris) does for P25...... I think
it will come sooner than later. We are, after all, part 97.. not part 90
here.. My R & D budget is a lot less than Icom or Motorola... but if we
do not try... we never will get there...as has been said
before..necessity is the mother of invention...
In my state we authorize 25k0 modulation on 12k5 centers in non
overlapping areas of operation... both use 16k0f3e deviation masks so I
am not really worried about trying to set 6k25's adjacent TODAY... For
now I think we are safe using 12k5 channel masks and channel centers for
coordination ...and operate there on 6k25's and we will worry about
getting closer as equipment gets better...
As has been pointed out by others.. we have lots of non used
repeaters.. In most of the US..we are not really in a spectrum crunch..
we are in a political crunch to figure out what constitutes
underutilized and how to-be-recovered pairs can be returned for re-use.
For the most part.. in amateur...6k25 is necessary only because it is
the D-Star SPEC... not because we have that great of spectrum issues in
most of the country..technology will catch up as need arises...and I do
not think most places we are there yet.
Doug
KD8B
Jeff DePolo wrote:
>
>
>
> > Anyone who is currently building analog AllStar Link
> > repeaters using a DMK URI already has the parts for a D-Star
> > repeater .. assuming your TX and RX will handle GMSK data of
> > your repeater.. This includes many Mastr II stations which
> > seem to be a large portion of the amateur repeater world..
>
> What are people doing about narrowbanding the RF hardware? There's no
> geo-spectral advantage to be gained by using D-Star/GMSK with a
> theoretical
> OBW of 6 kHz when the RF equipment is still wideband (mainly Rx IF,
> but also
> Tx must also be limited and LPF'ed).
>
> --- Jeff WN3A
>
