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Re: Manchester mod



On Mon, 4 Oct 1999, Bob Bruninga wrote:

> I got this from Tim, N8DEU who was the first to build my suggested
> Manchester mod to the TAPR-2.... for uplinking to AO16/LO19/IO26:
> 
> "Actually, I inverted the clock because it did not appear to be
> working.  After looking at a PSK-1 modulator design for the
> disconnect header I found the clock is inverted through the use
> of  a divider chip.  Thus, it struck me to try inverting the clock
> and wall-la it worked."
> 
> So in addition to the XOR gate, you may need an inverter too.
> But on my TINY-2 schematic there is an inverter already on the TXD
> so maybe it would also work if you simply XORED the non-inverted TXD with 
> the existing clock?  Thus you may not need the inverter.
> 
> Anyway, somthing to expermient with...
> 
> I ask the theorists, of the four ways to XOR clock and data, will only 1
> work, or will two of them work?

Since AX.25 data is sent in NRZI format, the phase of the clock
used to produce Manchester encoded data (or BPSK) shouldn't matter
because the phase of the Manchester encoded data doesn't matter.  :-)


73, de John, KD2BD

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