[InHam] Fwd: [IndianaD-STAR] Re: Indiana Repeater Council Meeting

[Mark Thompson]

----- Forwarded Message ----
From: "Stephen M. Parker, WR9A" <wr9aradio at gmail.com>
To: IndianaD-STAR at yahoogroups.com
Sent: Tue, July 12, 2011 4:09:45 PM
Subject: [IndianaD-STAR] Re: Indiana Repeater Council Meeting

Here is the full text of the IRC D-STAR Proposal, as submitted by
Charlie, N9MEW, at the Indy Hamfest IRC Meeting on July 9, 2011:
__________________________________________

The IRC is proposing to change the way that we coordinate D-STAR
systems.  Currently we are assigning D-STAR to normal Analog channels.
We will be using a plan similar to one of the adjacent states.  We
have several D-STAR applications pending.

We propose to offset the D-STAR carriers either 5.0 KHz or 6.25 KHz.

At this time, we are encouraging the incumbents to change frequency,
but we will not require that.  The present D-STAR HOC’s will be
notified individually the offset that we propose.

Each analog channel will accommodate Two D-STAR systems.
Theoretically two adjacent channels can be accommodated in the same
location.  This has not been tried yet by another state.  A different
state has placed them as close as 10 miles. We will not go that close.

For 2 meters, both the 15 KHz channels, and the 20 KHz channels will
use plus or minus 5.0 KHz offsets from the analog channel center.  The
15 KHz channels make a tight fit, but is workable.  We normally
require more distance to the adjacent channels for the 15 KHz
channels, than we do for the 20 KHz channels.

For 70 cm and other bands that use 25 KHz channels, we will use plus
or minus 6.25 KHz. Offsets.  This is a good fit.

There are several benefits to use the offsets.  First, we can
accommodate more D-STAR systems, in that the channels can be shared,
and it will minimize interference on the analog channels.

Some Coordination bodies have certain frequencies assigned only for
D-STAR use.   Indiana does not have any frequencies available over the
complete state.

A plus or minus offset will be selected by the coordinator depending
on how close the adjacent channel is.  This is especially important on
the 15 KHz 2 Meter channels.

Normal center channel repeater spacing will be used, for D-STAR, as
for Analog channels.  We may assign another D-Star system to the other
offset channels, depending on adjacent channels and other factors.

A note. D-STAR and Analog cannot share the same channel at the same
location. If the channel/location is used for D-STAR, then normal
mileage spacing is required to place an analog system on that channel,
per the chart that the IRC coordinators use.
__________________________________________

As has been previously mentioned on this reflector, it was voted on at
the meeting to change all references in that document from "D-STAR" to
"Narrow-band digital", in order to accommodate other digital voice
modes such as APCO-25. Otherwise, the document passed out at the
meeting is as stated above.

I have added my own notes about this topic below:

Here is an EXCELLENT web page with details about D-STAR bandwidth and
the results of extensive testing (with laboratory-grade equipment by
real RF engineers) in the real-world of D-STAR and analog FM repeaters
coexisting:
http://utahvhfs.org/dstar_channel_spacing.html

Here is what I think are very relative paragraphs from that web page:

"The relative "narrowness" of the D-Star signal is oft-touted as one
of its strong points.  To be sure, more of the total transmitted
energy is confined near the center frequency than is the case for the
analog signal.  For the D-Star signal, the majority of the energy is
constrained to within +-3.6 kHz of the center frequency.  In the case
of the analog signal, the majority of the energy is constrained to
within +-5 kHz of the center frequency.  This only tells part of the
story:  If one looks at the -30dB points of the two signals, one notes
that the bandwidth of the D-Star and analog signals are +-5 kHz and
+-6 kHz, respectively - and it is the energy in these sidebands that,
in part, dictates adjacent-channel concerns.  If one considers just
the -30dB points of the transmit signals, a minimum D-Star to D-Star
spacing of 10 kHz and a D-Star to Analog spacing of 11 kHz is
suggested.

Perhaps even more important is the detection bandwidth of the
receiver.  Ideally, the D-Star's receiver's filter need only be wide
enough to accommodate the primary "hump" that contains the majority of
the energy - that is, out to +-3.6 kHz, or a total bandwidth of about
7.2 kHz, but practical considerations (manufacturing tolerances in the
manufacture of the filter, achievable shape factor, group delay,
expected transmit or receive frequency errors, etc.) require that the
filter be wider than this.  As mentioned previously, the -6dB
bandwidth of the IF in the IC-91AD is, in fact, 8.6kHz (+-4.3 kHz),
dropping to -30dB at 11.2kHz (+-5.6kHz).  It is largely the
combination of the receiver filtering plus the occupied bandwidth of
the adjacent signal that dictates the minimum spacing of two D-Star
signals.

Receivers designed for traditional analog FM use in amateur service
are designed for a signal with a +-5 kHz modulation, so the receivers'
filters are necessarily wider - typically 15 kHz wide at the -6 dB
bandwidth and about 21 kHz wide at the -30 dB bandwidth.  For this
reason - plus the fact that the analog signal is wider - it is
necessary that the spacing between an analog signal and either another
analog or even a D-Star signal must be wider than that between two
D-Star signals."

Bottom line quote from that article:
"Based on the above test data as well as frequency and spectral
analysis, the following are recommendations of the Utah VHF Society:
D-Star to D-Star channel spacing:  12.5 kHz minimum
D-Star to Analog channel spacing:  15 kHz minimum"

In addition, here a link to an excellent technical article on the
subject, as well:
http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/Dstar_Co.pdf

________________________________________
Stephen M. Parker, WR9A
WR9Aradio at gmail.com
________________________________________


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