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Re: APRS and Digital 2-ways



Hi Bob and others:

An "Idea" for mixing APRS and DIGITAL 2-way QSO's on a single FM satellite
channel. 

Background:

Listen to AO-27 on a weekend. If the right people are on and cooperate
it has been possible to almost get 2-ways between 18 different hams on the
satellite in one pass. In thinking how this worked and giving up on training
and getting the hams to follow it I thought it might work if it was enforced
by the satellite software and done with all users using 9600 bps packet.

The same problem exist on Mir. Some people are trying to use the BBS,
others are trying for 2-ways and now others are trying to do APRS.

How and When:

I am working on the JAWSAT amateur satellite that is scheduled to be 
launched in September of this year. It should have two VHF 2m uplinks
(145.960 MHz and 145.xxx) and two UHF 70cm (437.175 and 437.075) downlinks.
Each can do 9k6 packet and voice.

As of now we do not plan on it being a store and forward BBS. It will have
files to be downloaded by WISP but uploading from WISP will not be
implemented. At some point down the way (approx. 6 months) I may be able to
experiment with some new digital modes. A FM bent pipe will be on one pair
of frequencies and the other will be for the digital.

At the bottom of this posting is my reply about dumb terminal UI packet
users on Mir. I have ex paned on it with reply to Bob reply. I hope to have
time to expand on it more in several months.

		But for now here is my reply to Bobs reply.

Bob
At 01:16 AM 6/5/99 -0400, you wrote:
>Don't confuse a 2-way with requiring an ACK.  Two differnet animals.
>
>ANyone can do a 2 way via MIR or any poor channel.  Just keep trying.
>
>But if the chance is 10% of a packet getting through, then the chance of
>getting an ACK back is 10% of 10% or 1%.   AND NOONE wants to watch you
>send your message 100 times just to get the ack.

The ACK I was referring to was another packet from the other station with
my callsign in it. If he knows he had it repeated by Mir then he knows I could
have seen it.  It helps if you can run full duplex so you hear every thing
coming down from the satellite. From Mir this is hard unless you gateway it
out on another frequency from a remote location.  On the 9600 birds it will
be easier. JAWSAT could downlink on 70cm with 8 watts with a receiver on the
ground like the PCR-1000 with AFC, it adjust for Doppler.  You need
some good filters to wipe out your 2 meter harmonics.

>If two stations are doing a 2-way without waiting for acks, then each one

Once again not an ack from mir but a packet from the other ground station
with some information so you know it was directed at you.

>gets 10% probabilty which isnt too bad... It would be bad to write any
>code that demands ACKS via a poor channel...  Unless you then add
>redundancy to the ACK.  APRSdos does this, but Mac/Win/APRS+SA dont...

The code would be like the PACSATs in that there will be a PB packet that
would be a queue of callsigns requesting to do 2 ways contacts. When
your call came first on the queue you would then send your information for
each of the other calls on the queue to the satellite which would then
transmit it.  If the first entry on the queue is CQ then stations can send
their grid locator and ask to be added to the queue.

When it is your turn to transmit you could send your APRS format to APRS
and it would be relayed back to a central ground station for insertion into
the Internet.  The satellite would also kept a record of all the successful
2-ways in a log which could be downlinked to the ground in a compressed
format.
The log could be used to verify 2-ways for awards, QSL card checking etc.

>> >Our chances of convincing them to type in our format is small...  oh
>> >well...

Please put the format some place on your APRS home pages where one can find
it. There are lots of pointers to the various programs but not many how to
do it on MIR without one of the APRS programs.
 
73, Randy

=========================================================================
		Here is my original reply to Bob
=========================================================================

> At 10:38 PM 6/4/99 -0400, you wrote:
> >On Fri, 4 Jun 1999, Thomas M. Schaefer wrote:
> >
> >> Well, on the 1852 pass and the 1715 (MDT) passes, both times I saw my
> packet
> >> repeated by the D7. I heard lots of stations on my mobile rig, but not
much
> >> on the D7.
> >
> >Yep, I notice that too... Problem is that the THD7 will only see standard
> >APRS stations and other THD7's.  It will not see other dumb-terminal UI
> >users.  And the majority of users on the MIR channel are such UI users.
> 
> Maybe we want to see if someone is connected to the Mir BBS before we send
> our UI packets.
> 
> >Our chances of convincing them to type in our format is small...  oh
> >well...
> 
> Maybe not if you add an extension so we could request an acknowledgement
> from a particular callsign. That way you could track where we
> are and we could get a 2-way exchange so it qualifies for one of the 
> awards (VUCC, WAS etc) on Satellite. I would write my own program to look
> for calls that are in of the grid squares that I was looking for and send
> a request to those callsigns only.  
> 
> Better yet if you did that I might leave my OSCAR station on all the time
> and gateway the calls into the Internet.
> 
> I am not the only one who gets frustrated when I hear some in a grid square
> I have been trying to work for several years.  Can you just imagine the
> uproar if someone got on HF from a rare DXCC county and just transmitted 
> "Hey! I am on Heard Island" for example but would not do any 2 way contacts.
> 
> I am the one doing the communications for JAWSAT and also helping out on the
> flight software.  I may implement a digital queued 2-WAY QSO system on
JAWSAT
> that would allow for a maximum of exchanges on one FM channel (VHF up/UHF
> down).
> I could enhance it so it would let APRS be digipeated and play in the queue.
> I may only do that if there is someway to get 2way contacts with the APRS
> ground stations.
> 
> 73, Randy N7SFI
> 
> 

---------------------------------------------------

73, Randy N7SFI

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