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

[Eric Knaps, ON4HF]

Hi there,

Do you really think that the European alligators will wait for 3 seconds?


Op 21/06/2010 16:04, Jan-Albert Koekemoer schreef:
> 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)
>
>
>
>
>
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>
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>    

-- 
Amateur Radio Station ON4HF
Eric Knaps
Satellite manager UBA

Tel. +32472985876 (mobile)

http://www.on4hf.be