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How to mod your G3RUH 400 bps decoder from 512 to 514--? was Re: [amsat-bb] No Checksum on P3T?



Hi Howard,

I could be wrong, but here goes..

The "old style" P3 telemetry decoders can only do 512 byte blocks---so you 
will not be able to have a checksum check of the block (which requires the 
514 bytes).

Simply put-- won't do checksum as is.

Now, what I do NOT know is if your unit is somehow modifiable/upgradeable 
to do 514 byte blocks with CRC.  I bet James G3RUH's site where he sells 
the units/boards might comment on that?

WAIT---I just found out where the mod information is :-)

In this file are images and text describing how to do it:

http://www.amsat.org/amsat/ftp/satinfo/ao13/demod.zip


Here is an extract of one of the files
---------
Modifications to original 1984 AO-10 Data Demodulator   (MK I)
--------------------------------------------------------------

The original G3RUH demodulator, issued in 1984, outputs 512 bytes per block
(i.e. CRCC bytes are discarded) and has a serial output not at true +/-12 volt
levels.

In this directory are two GIF files that depict the circuit changes you
can make to output 514 bytes/block, and add an RS232 level interface.

In addition, there are some essential component value changes that improve
the PLL performance considerably.  These are:

  R7  330k    C10   1n hi-stab 5%
  R9  150k    C11  47n
  R10 470k    C12   4n7 hi-stab 5%
  R12 330k    C13  47n
  R14 330k    C16  10n
  R17 100R    VR3  50k

Note that the 4046 PLLs are very voltage sensitive, so use a 12v stabilised
supply.

James Miller G3RUH   1994 May 01
<eof>
--------------

Good luck with your mod!  Let us know how it goes...

73,

Mark N8MH


At 04:29 PM 12/4/00 +0000, Howard Z wrote:
>I am using an old homebrew I think it's a G3RUH or something similar 
>(can't really remember ) PSK converter from my AO13 days , Can someone 
>please tell me why I receive no checksum and only receive RAW data , I 
>have tried 512 and 514 bits , is my converter somehow obsolete ..
>
>Thanks
>
>Howard VE2AED

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