[amsat-bb] Re: DSTAR vs AO-51

Tony Langdon vk3jed at gmail.com
Mon Apr 27 16:37:09 PDT 2009

At 06:03 PM 4/27/2009, Luc Leblanc wrote:
>On 27 Apr 2009 at 6:42, Tony Langdon wrote:

> >
>That's exactly what i discover compensating for doppler in 5kc steps 
>is probably not enough on on the downconverter IF it puts the signal
>too much in the on an off state having to play back and forth with 
>the knob.  My problem is a rig limitation i'm stuck with a monoband
>DSTAR radio making it useless on V/U mode. The only one way is to 
>find a way to convert UHF to VHF in the 144mhz region to avoid desense.
>As far i remember it is far from an ideal solution but i think some 
>are able to do it?

I see.  I can't run duplex in D-STAR anyway, would need a second 
radio, or an FM box with Jakub's D-STAR Decoder software and a DV 
Dongle running on a PC.  That could solve the 5 kHz step problem, 
because I could tap the discriminator of an all mode radio, and tune 
in 1 kHz or smaller steps.  I would need to use a 70cm downconverter, 
as I have no all mode gear on 70cm, but I happen to have one of those 
handy.  Hmm, might be a worthwhile project for those of us D-STAR 
users with spare gear and a dongle, and are able to do the necessary mods.

>I note Drew's offer but due to my rig limitation i will not be able 
>to use it. This don't mean if someone else with a DSTAR dual band
>want's to try i will not try to uplink few data stream but i will 
>not be able to hear myself :(

Cooperation between a few local hams would yield results, as would 
the method above.

>Again with what i have here S mode can work as i will only have to 
>change my Down Converter IF from 123mhz to 145mhz that can be done
>easily with but the 5kc steps issue. On some rig the steps are 
>adjustable i don't know if the IC2200H can do that as the menus settings on
>this rig is probably the worse i never seen yet. You have to 
>have  manual always with you...

Most FM rigs have 5 kHz as the smallest step available.  The problem 
with 2.4 GHz is the insane rate of Doppler shift, unless you have 
computer control of something in the chain, it's going to be 
extremely difficult to maintain a lock on D-STAR, especially if 
you're stuck with 5 kHz steps.  I don't have computer control here, 
so that's not an option for me.

>P.S. I don't know why nobody never speak about DSTAR here on this BB 
>as some are avid data satellites advocate and DSTAR can transmit APRS
>signal called DPRS plus voice at the same time even slow data 
>messages? Is two DSTAR modules plus a controller unit operating cross band
>flying aboard ISS is possible? With an high speed data 1.2ghz module 
>is it possible to have fast internet access from space? Tapping in the
>next internet ISS lan system? I'm guessing Icom can be interested to 
>offer the hardware if it's to be flown aboard ISS!!
>In bonus it will offer some spare/off time activities for the next 6 
>members crew. Could be ARISS can be interested too?

I can't see 1.2 GHz working.  As far as I know, it's an uplink only 
band, and DD mode works in simplex mode, so it wouldn't be legal in 
the Amateur Satellite service, without modification to work split 
band (say 1.2/2.4 GHz).  Haven't done the path loss calculations, to 
see if it's viable with 10W and a decent gain antenna.

73 de VK3JED / VK3IRL

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