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[hfsig] Performance of 24/192 soundcards? USB Soundcards

Alexander Kurpiers a.kurpiers at nt.tu-darmstadt.de
Wed Sep 22 13:59:06 UTC 2004


Mark Jordan wrote:
> 	Hi Anthony,
> 
> 	I have sent you a 200kb ZIP file with the G3RUH circuit and partlist.
> 	It would be very interesting having a 9k6bps modem that works without
> needing DC frequency response.

This could already be done with the original modem design, you just need a 
DFE in the receiver.
This is done e.g. in the ALEF NULL project (see PAM-Signaling) 
ftp://ftp.tapr.org/dsp/Motorola/dsp56001/dsp_card_4/doc2.pdf

The problem is: if you have a transceiver with bad DC response a receiver 
with DFE could still be used. But nobody we a "normal" receiver can copy 
your signal well. So you better go and improve your TX to be "compatible"...
I would perhaps make sense to have something like that in the receiver of 
the digipeater to allow the users to have a bad DC response.
Question is: is anybody still interested in 9k6 anyway :-(

>>
>>>http://www.amsat.org/amsat-new/archive/index.php?t
>>
>>=./articles/James_Miller
>>
>>Thanks.
>>
>>The G3RUH circuits are here yes. But the type numbers of all the
>>chips are not on the circuit, and even the pin names (eg. clk) have
>>been omitted, leaving me clueless if U1 is a counter or a shift register!
>>
>>
>>>He was making a modem compatible with the K9NG modem, so the
>>>scrambler algorithm and its place in the grand scheme of things
>>>were already constrained.
>>
>>Indeed. Amateurs (and Pro's) often build on what someone else has done
>>irrespective on whether it was right or good or just plain obsolete.
>>It's called "Engineering".
>>
>>My suggestion is that the receiver could be improved without change
>>to the Tx, so interoperability is unchanged or improved.




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