[Dstar] D-Star Bandwidth

Fri Dec 12 23:48:42 CST 2008

Steven,

Thank you for the reply. I'm afraid I have no technical  knowledge of worth,
on the D-star process. Certainly not enough to calculate a modulation index
for the requirement. It is obvious that D-Star as we have had it supplied,
is in a platform that is compatible with existing FM repeater  systems. That
is of course what you have tested. I wonder, if it was put into a special
digital transceiver of minimal bandwidth requirement, what that requirement
would be?    Would it be 2.7KHz, and that is similar to a SSB transmission? 

Would the data rate effect the bandwidth? Would this increase it to your
6.25KHz? or is it 6.25KHz simply to increase the audio level in a wide
demodulation environment? 

I believe that in the future bandwidth will be a important consideration in
all amateur communications. We are of course still in the 1960s with our FM
transmissions. I remember that in Australia , in 1965 we went from 60 KHz to
30KHz in commercial networks which has translated to 25 KHz  allocated in
the amateur service. 

VK2BZ

From: dstar-bounces at lists.wia.org.au [mailto:dstar-bounces at lists.wia.org.au]
On Behalf Of Steven Samuel Bosshard (NU5D)
Sent: Friday, 12 December 2008 10:52 PM
To: Dstar Digital Radio Mail List
Subject: Re: [Dstar] D-Star Bandwidth

G'Day Barry and the list,

I did run some measurements on dstar using a 91ad talkie and have spectrum
display pictures of my measurements.  The advertised bandwidth is 6.25 kHz
and just squeaks by the 26 dB sideband points.  26 dB is the power points
used to define occupied bandwidth in amateur service.  In commercial (PMR)
service the power points are more like 63dB and at this point the occupied
bandwidth measures 12.5 kHz.  This is from looking at a spectrum analyzer
display and there is certainly some error from government laboratory
measurements - also I am going from memory on the 26 dB and 63 dB points but
I believe these to be reasonably close, if not exact.

In testing a dstar receiver I used a 1000 Hz FM tone modulated at +/- 2.5
kHz transmitter deviation with a signal level around -119 dBm and listening
with a SINAD meter and audio monitor to the discriminator point in the
repeater receiver.  Seems like distortion increased dramatically after I ran
past 3.5 kHz on the generator FM deviation.

So,  30 kHz may refer to the channel spacing, but not at all the occupied
bandwidth that is more like 12.5 kHz.  I believe dstar transmitters can be
placed on adjacent 12.5 kHz channels if there is some geographic separation
or a guard band between channels.

I do hope this is what you were looking for.

73 and Best Christmas wishes,  Steve NU5D

Barry Sullivan wrote: 

Hi, 

I have a question that some very knowledgeable person may consider answering
for me. 

That is: "Why do we need to use transceivers with 30KHz band requirements
when I'm told D-Star only needs 2.7 KHz band width." 

I reason that if only 2.7 KHz is needed then any attempt to move to that
band width would only need a modulation and limiter adjustment in the Tx but
new receive filters in the Rx. 

Therefore is there any provision to permit modification of the current
generation of D-Star radios? 

I think the question is important as there is a current review taking place
of the 400MHz spectrum usage and we may find ourselves very limited in
spectrum allocation in that band. 

VK2BZ  

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