[amsat-bb] Re: Yes, DStar can work on LEO,

Mon Feb 26 19:32:41 PST 2007

If the high speed data modes will work, then digital voice should also.  
The DV may not sound like the telephone quality we are used to hearing, 
but the only difference would be the D/A conversion that puts the ones 
and zeros out the speaker instead of  on the screen or paper.  You may 
have to wait for the buffer to fill and output the speach as often 
happens on slow VoIP connections.  We are used to that when someone is 
using vox and AAAahhhhhhhhhhhhhs alot to keep the vox from reacting.  
38k4 may be too slow to avoid this, but how long ago did we just have 
300 baud data or 45 baud TTY.  QRM and QRN will be great obstacles to 
overcome, not to mention the acquire LOCK time before roundtables become 
commonplace.

73,
Jim

MM wrote:

>In my first memo about Digital Audio on Satellites I
>did not have time to go over a few other outstanding
>issues, such as Inverting Transponders and Doppler on
>the 440 band.
>
>Will DV work on Inverting Transponders?
>I do not know.  My guess is that Non-inverting would
>work better, but that's just a guess.
>Let's try it and find out.
>
>Doppler on 440.
>The Doppler on 440 is plus and minus 10 kHz.  That is
>too much for the ID-800 and similar radios running
>digital audio.  Normal FM 5k deviation voice can work
>find at 3 kHz frequency error and is even usable with
>noise up to 6 kHz of frequency error.  Digital Voice
>would work best on 10 meter / 2 meter satellites, with
>non-inverting transponders.  Maybe AO-7 could work. 
>The other satellite VUSat-OSCAR 52 is inverting.
>
>Future Radios:  Wish List
>Most mobile radios made today are designed for channel
>steps starting at 5 kHz, 6.25, etc.
>It would be desirable if manufactures would design
>their rigs for smaller channels steps to allow us a
>little more flexibility in using them for FM
>satellites.  It would not add much cost to a typical
>FM mobile rig to allow 1.0 kHz and 2.5 kHz channel
>steps.  For FM satellites you do not need to be
>exactly on frequency.  You just need to be in the ball
>park (plus and minus 2.5 kHz works).
>
>Miles
>--- Dave hartzell <hartzell at gmail.com> wrote:
>
>  
>
>>Will this still work on an inverting transponder?
>>
>>On 2/26/07, MM <ka1rrw at yahoo.com> wrote:
>>    
>>
>>>The Icom IC-800 will work with some Doppler Error
>>>      
>>>
>>in
>>    
>>
>>>Digital voice mode.
>>>I have been testing the IC-800 specifically to see
>>>      
>>>
>>how
>>    
>>
>>>well it would work in theory with a 2-meter signal
>>>from a simulated LEO Orbit, such as ISS at 240
>>>      
>>>
>>miles
>>    
>>
>>>altitude.
>>>The results have been very promising on Earth.
>>>
>>>The IC-800 will decode good Digital voice, with a
>>>frequency error of > 2.5 kHz.
>>>And this was at an indicated signal level of S1 on
>>>      
>>>
>>the
>>    
>>
>>>radios S-Meter.
>>>At higher S-Signal levels the amount of frequency
>>>error the IC-800 can tolerate in digital voice
>>>      
>>>
>>mode is
>>    
>>
>>>higher.
>>>
>>>I setup a pair of IC-800 20 miles away.  Then by
>>>      
>>>
>>using
>>    
>>
>>>a combination of 5k channels on one radio and
>>>      
>>>
>>6.25k
>>    
>>
>>>channels on the other radio, i was able to
>>>      
>>>
>>simulate 2,
>>    
>>
>>>2.5k and 3k channel doppler errors.  A beam
>>>      
>>>
>>antenna
>>    
>>
>>>was used to Lower the indicated Signals levels
>>>      
>>>
>>until
>>    
>>
>>>audio quality droped.
>>>
>>>The lower the altitude the higher the Doppler
>>>(Frequency dependant too).  The Doppler from ISS
>>>      
>>>
>>is
>>    
>>
>>>approximately Plus and Minus 3.3 kHz.  This means
>>>      
>>>
>>that
>>    
>>
>>>If a LEO satellite is approaching on 2-meters, the
>>>frequency you will see on your radio will be up to
>>>      
>>>
>>3.3
>>    
>>
>>>kHz higher for the first minute, then will quickly
>>>drop to zero Doppler for a few seconds at the 5
>>>      
>>>
>>minute
>>    
>>
>>>mark (assuming a 10 minute pass).
>>>
>>>So, in theory, if the Doppler on a transponder
>>>      
>>>
>>based
>>    
>>
>>>satellite is less than 3 kHz and you have signals
>>>stronger than 1 S-Unit, it should be possible for
>>>2-way Leo satellite via digital voice.  Anyone
>>>      
>>>
>>else
>>    
>>
>>>have an IC-800 and want to test?
>>>
>>>Miles WF1F
>>>
>>>www.marexmg.org
>>>
>>>ka1rrw at yahoo.com
>>>
>>>
>>>
>>>
>>>
>>>
>>>      
>>>
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>>>
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>>-- 
>>"It is far better to grasp the Universe as it really
>>is than to
>>persist in delusion, however satisfying and
>>reassuring." - Carl Sagan.
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