[amsat-bb] Re: SO-67 back on air!
pe0sat at vgnet.nl
Mon Jun 21 11:55:40 PDT 2010
On Mon, June 21, 2010 20:01, Eric Knaps, ON4HF wrote:
> Hi there,
> 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:
>> After much delay we are now in a position to re-activate the SA-AMSAT
>> schedules on a regular basis again!
>> During the downtime we conducted several experiments in order to
>> possible alternatives for the "cut-off" problem experienced by many at
>> 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
>> onto the transmitter for about 3s after a specific ground transmission
>> ended, whereafter the received audio is cut off. The SW then waits for
>> next ground transmission with a valid "transponder" tone embedded,
>> gating the audio onto the transmitter again. So if a second
>> starts within the 3s "tail" period, it will be cut off when the 3s
>> 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
>> that should be of some assistance when using the payload: the PTT of
>> 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
>> not get rid of the "cut-off" problem, nor of the requirement to embed a
>> 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"
>> embedded in the transmission) and the transmission is relayed on UHF
>> 3. When Person A releases his/her PTT, the satellite will continue
>> transmit what it is receiving (usually this will be "noise") for a
>> ±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
>> using the SA-AMSAT payload on SO-67.
>> I will request Gladys Magagula at the Satellite Application Centre to
>> regular schedules from the regional coordinators as soon as possible.
>> will start off with day passes only, transmit on 2.5W and see how things
More information about the AMSAT-BB