[amsat-bb] Re: SO-67 back on air!

[Ron Overdrive]

Honestly sounds like a good way to keep people from doubling/tripling up on
each other. Might end up making more contacts per pass if everyone is forced
to wait between transmissions to be heard.

On Mon, Jun 21, 2010 at 10:04 AM, Jan-Albert Koekemoer <
jan.koekemoer at sunspace.co.za> wrote:

> Hello
>
>
>
> After much delay we are now in a position to re-activate the SA-AMSAT
> payload
> schedules on a regular basis again!
>
>
>
> During the downtime we conducted several experiments in order to
> investigate
> possible alternatives for the "cut-off" problem experienced by many at the
> end of last year / beginning of this year.  The cut-off is caused by SW
> running on piggyback electronics that continues to gate the received audio
> onto the transmitter for about 3s after a specific ground transmission has
> ended, whereafter the received audio is cut off.  The SW then waits for the
> next ground transmission with a valid "transponder" tone embedded, before
> gating the audio onto the transmitter again.  So if a second transmission
> starts within the 3s "tail" period, it will be cut off when the 3s expires.
> Listen to this mp3 recording as an example:  http://tinyurl.com/38vvg3o
>
>
>
> Unfortunately the piggyback electronics does not have reprogramming
> functionality, so we are not able to change the SW.  We did however manage
> to
> implement a mechanism on the satellite transponder (used by the piggyback)
> that should be of some assistance when using the payload:  the PTT of the
> transmitter now STAYS ON for the duration of the payload activation (i.e.
> 15
> min), regardless of a valid "transponder" tone received.  Note that this
> does
> not get rid of the "cut-off" problem, nor of the requirement to embed a
> valid
> tone when you want to use the payload - see detailed explanation below.
>
>
>
> The following example depicts the ideal usage scenario of the payload:
>
> 1.       As the satellite comes over the horizon, an unmodulated carrier
> ("quieting") will be received by all on UHF
>
> 2.       Person A starts to transmit on VHF (with valid "transponding" tone
> embedded in the transmission) and the transmission is relayed on UHF
>
> 3.       When Person A releases his/her PTT, the satellite will continue to
> transmit what it is receiving (usually this will be "noise") for a further
> ±3s.  Nobody should start to transmit during this time!
>
> 4.       At the end of the ±3s period, everybody will again hear the
> unmodulated carrier.
>
> 5.       NB: only when this unmodulated carrier is heard should Person B
> start to transmit.  Listen to this mp3 recording as an example of valid
> usage:  http://tinyurl.com/32rjbxm
>
>
>
> I suppose this will take some getting use to - at least the system has a
> built-in "punishment" mechanism for the impatient! ;-)
>
>
>
> Please refer to previous posts on general voice quality optimization when
> using the SA-AMSAT payload on SO-67.
>
>
>
> I will request Gladys Magagula at the Satellite Application Centre to
> obtain
> regular schedules from the regional coordinators as soon as possible.  We
> will start off with day passes only, transmit on 2.5W and see how things
> go.
>
>
>
> Enjoy!
>
>
>
> Regards
> Jan-Albert
>
>
>
> ________________________________________
>
> Jan-Albert Koekemoer, PrEng
>
> Sun Space & Information Systems (Pty) Ltd.
>
> Stellenbosch, South Africa
>
> www.sunspace.co.za <http://www.sunspace.co.za>
>
> +27 21 880 8117 (tel)
>
> +27 83 461 6643 (cell)
>
> +27 21 880 1703 (fax)
>
>
>
>
>
> E-mail Disclaimer
> http://www.sunspace.co.za/emaildisclaimer.htm
>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
>