[Dstar] D-Star Bandwidth

[Steven Samuel Bosshard (NU5D)]

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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-- 
A Decibel saved is a Decibel earned.....

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