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

[PE0SAT]

On Mon, June 21, 2010 20:01, Eric Knaps, ON4HF wrote:
> Hi there,

Hi Eric,

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

I rest my case :))

Perhaps when the crocodiles have read this, things wil change?

Some self-reflection would be appropriate ...

73 Jan PE0SAT

> 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!