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Re: Telemetry sync sequence?



Randy:

All of the software demods for the DSP1232/2232 and EVM and
the hardware demods, such as G3RUH,  look for the sync vector,
but it is not passed out for processing.  It is only used internally
for frame sync.   Some of these, raise and lower RS-232 signals
when a frame is detected and after it is done.

Is this what you meant?  If you are looking at the raw demodulated
bits you may have forgotten that the data is  encoded (the next
transmitted bit is the XOR of the current transmitted bit and the
new actual data bit).  This is true in both data and sync.  And the
bit order in the data bytes is high order bit  of each byte is sent first.
There was a modem built into the old AO-10 and AO-13 lash ups for
sending a convolutional code of the data.   I am uncertain if this was
included on this bird but the rationale for doing so would be the
same, we have a weak emitter for some reason and to get valid
telemetry, we need encoding.  What we have appears to be
doing the job, most especially with this behemoth of a transmitter.

Bob

----- Original Message -----
From: "Eric A. Cottrell" <eac@shore.net>
To: <hamradio@oz.net>
Cc: <amsat-bb@AMSAT.Org>
Sent: Friday, November 24, 2000 5:54 PM
Subject: Re: [amsat-bb] Telemetry sync sequence?


> Randy wrote:
> >
> > Hi:
> >      According to the P3D telemetry information I downloaded from
> > AMSAT-DL (www.amsat-dl.org/p3d/tlmspec.txt) dated 01 November 2000 the
> > P3D telemetry should include a sync sequence preceeding each data block
> > consisting of #39 #15 #ED #30.  Does anyone know if this is what is
> > actually being sent?  I have been looking at the data and I have not
> > found these bytes in the data stream.  Am I doing something wrong or has
> > there been a slight telemetry format change?
>
> Hello,
>
> What are you using for decode?
>
> I know with the AEA DSP-2232 (and others?) the sync sequence is not
outputed
> to the computer.  It is used by the DSP modem to synchronize the data
stream.
>
> I assume other modems (including G3RUH) do the same as P3T works well with
> the DSP-2232 not outputing the sync.
>
> Another part that is not outputted is the idle characters inserted between
> telemetry frames.
>
> 73 Eric eac@shore.net  WB1HBU
> ----
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>

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