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Re: GPSL Flights... time slotting to enable sharing 144.34 ?

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  • Zack Clobes
    I think time slotting is going to be very important for this year s event. Can someone please define EXACTLY what the accepted definition of time-slotted is?
    Message 1 of 4 , Feb 23, 2004
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      I think time slotting is going to be very important for this year's event.

      Can someone please define EXACTLY what the accepted definition of time-slotted is?  For example, if you're time-slotted at 10 seconds, when do you begin your transmit and how long do you have to transmit?  Do you begin your transmission as soon as you decode the GPGGA string with 10 seconds in it, or do you start after you receive the 09 seconds?


      Is six seconds per minute sufficient time for each group to transmit their needed data?  That would give us 10 balloons on a single frequency with posits every 60 seconds.

      Zack

      K. Mark Caviezel wrote:
      With this many payloads aloft from the same site at
      the same time,
      frequency and time slotting coordination becomes a
      fairly important
      hair-pulling exercise, Zack.
          
      Zack: Mike raises an excellent point.   I'll point out
      that the TinyTrak-supported "time slotting" function
      worked great for two payloads during GPSL 2003 (I
      think it was EOSS's K0YUK-11 and "ES-OS"'s KC0JHQ-11
      beacons < I don't think the EOSS 67 recap fully
      captured all of the frequency assignments as there was
      some last minute juggling>).  Since the time slotting
      is based off of GPS derived time, the relative timing
      can be very accurate, you could probably get reliable
      position updates once a minute from 30 or 60 TT based
      APRS trackers all sharing the same frequency.   I know
      many of the groups coming to GPSL already have a
      TinyTrak and I will suggest that all groups could fly
      a beacon on one frequency such as 144.34 MHz and time
      slot them to enable QRM-free sharing of a single
      frequency.   As long as no payload suffers from 'dead
      key up' this will work fine. 
      
      We'll rely on you to be the point contact for
      frequency co-ordination/QRM elimination.   I'll submit
      a request to fly an APRS beacon on 144.34 MHz, one
      packet per minute at the top of the minute (:00).  
      And, yes, I am sticking to my plans of flying a 1/2
      million cubic foot plastic balloon at GPSL, with good
      prospect of capturing displacement and absolute
      altitude records.  (although now I need to build this
      monster!)    
      
      
      - KMC 
        
    • Mark Conner
      I think the definition should be that the actual transmission occurs between the seconds specified. The participant should program their device to compute
      Message 2 of 4 , Feb 23, 2004
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        I think the definition should be that the actual transmission occurs between the seconds specified.  The participant should program their device to "compute early" by the number of seconds necessary for formatting, etc., by their device. 
         
        Also, chase teams should ensure they have their ground stations disabled from transmitting on 144.34.  We don't care where your car is, just your balloon.  :-P
         
        73 de Mark N9XTN
         
        ----- Original Message -----
        Sent: Monday, February 23, 2004 19:48
        Subject: [GPSL] Re: GPSL Flights... time slotting to enable sharing 144.34 ?

        I think time slotting is going to be very important for this year's event.

        Can someone please define EXACTLY what the accepted definition of time-slotted is?  For example, if you're time-slotted at 10 seconds, when do you begin your transmit and how long do you have to transmit?  Do you begin your transmission as soon as you decode the GPGGA string with 10 seconds in it, or do you start after you receive the 09 seconds?


        Is six seconds per minute sufficient time for each group to transmit their needed data?  That would give us 10 balloons on a single frequency with posits every 60 seconds.

        Zack


      • paul.verhage@boiseschools.org
        Once a minute is fine for me. Paul
        Message 3 of 4 , Feb 24, 2004
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          Once a minute is fine for me.

          Paul

          > Is six seconds per minute sufficient time for each group to transmit their needed data? That would
          > give us 10 balloons on a single frequency with posits every 60 seconds.
        • Mike Manes
          Hi Zack, I think that 60-sec APRS reporting intervals should be plenty often for the GPSL balloons. And the time-slotting is only necessary for those APRS
          Message 4 of 4 , Feb 25, 2004
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            Hi Zack,

            I think that 60-sec APRS reporting intervals should be plenty often
            for the GPSL balloons. And the time-slotting is only necessary for
            those APRS beacons that share a common beacon freq, e.g. 144.34. I
            think ANSR uses a 70 cm freq for theirs, so they needn't time slot
            if no one else is on freq. So probably 10-sec slots will suffice with
            60-sec GGA beacons. Each beacon takes under 2 sec to transmit.

            Now, time slotting works right only when all beacons are using identical
            real time references, usually the time stamp on the GPS GGA sentence.
            The TinTrak beacon and KPC-3+ beacons can be set up to time slot, but
            the KPC-3+ requires you to preset a START time, after which the time
            slotting will begin. This means that you gotta get a good GPS
            acquistion
            before the START time, which should be BEFORE launch! Takes some
            godd guesswork and launch coordianation! On GPSL 2003, I blew it,
            but was able to recover by going into remote sysop mode just moments
            before launch and corrected the START time to 2 minutes later; it
            worked.

            73 de Mike W5VSI, EOSS

            > Zack Clobes wrote:
            >
            > I think time slotting is going to be very important for this year's
            > event.
            >
            > Can someone please define EXACTLY what the accepted definition of
            > time-slotted is? For example, if you're time-slotted at 10 seconds,
            > when do you begin your transmit and how long do you have to transmit?
            > Do you begin your transmission as soon as you decode the GPGGA string
            > with 10 seconds in it, or do you start after you receive the 09
            > seconds?
            >
            > Is six seconds per minute sufficient time for each group to transmit
            > their needed data? That would give us 10 balloons on a single
            > frequency with posits every 60 seconds.
            >
            > Zack
            >
            > K. Mark Caviezel wrote:
            >
            > >> With this many payloads aloft from the same site at
            > >> the same time,
            > >> frequency and time slotting coordination becomes a
            > >> fairly important
            > >> hair-pulling exercise, Zack.
            > >>
            > >>
            > > Zack: Mike raises an excellent point. I'll point out
            > > that the TinyTrak-supported "time slotting" function
            > > worked great for two payloads during GPSL 2003 (I
            > > think it was EOSS's K0YUK-11 and "ES-OS"'s KC0JHQ-11
            > > beacons < I don't think the EOSS 67 recap fully
            > > captured all of the frequency assignments as there was
            > > some last minute juggling>). Since the time slotting
            > > is based off of GPS derived time, the relative timing
            > > can be very accurate, you could probably get reliable
            > > position updates once a minute from 30 or 60 TT based
            > > APRS trackers all sharing the same frequency. I know
            > > many of the groups coming to GPSL already have a
            > > TinyTrak and I will suggest that all groups could fly
            > > a beacon on one frequency such as 144.34 MHz and time
            > > slot them to enable QRM-free sharing of a single
            > > frequency. As long as no payload suffers from 'dead
            > > key up' this will work fine.
            > >
            > > We'll rely on you to be the point contact for
            > > frequency co-ordination/QRM elimination. I'll submit
            > > a request to fly an APRS beacon on 144.34 MHz, one
            > > packet per minute at the top of the minute (:00).
            > > And, yes, I am sticking to my plans of flying a 1/2
            > > million cubic foot plastic balloon at GPSL, with good
            > > prospect of capturing displacement and absolute
            > > altitude records. (although now I need to build this
            > > monster!)
            > >
            > >
            > > - KMC
            > >
            > >
            >
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            --
            Mike Manes manes@... Tel: 303-979-4899
            "Things should be made as simple as possible, but not more so." A.
            Einstein
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