[RTTY] Sound Cards

[Ian White, G3SEK]

Kok Chen wrote:
>
>If the weakest detectable audio signal from the rig (post AGC) is at 
>least 5% of the max audio from the rig (i.e., 26 dB range or a loss of 
>4 bits full scale for the weak signal), I don't think you can ever see 
>better copy with a better ("more expensive") converter.
>
>But if the range of audio signals from the receiver is greater than 40 
>or 50 dB, you probably will see an improvement with more bits in the 
>converter if your operating system knows how to move more than 16 bits 
>of sampled data.  Again, just MHO.
>

By coincidence I have been trying to answer the same general question 
for my monthly column, and have been discussing it with Peter Martinez, 
G3PLX (Mr PSK31). Peter's view is that just about any modern sound card 
is good enough for amateur radio data applications. You certainly can 
measure objective differences between sound cards in the lab, but in 
radio applications these will be masked by much bigger variations in 
transceiver performance and the user setup of I/O levels.

To some extent, this is an obsolete question. Early PC sound cards were 
only just good enough, and some of them weren't, so differences between 
models could be important. But today, even the most basic sub-$20 PCI 
soundcard will have a chipset that outclasses anything you could buy ten 
years ago.

Recommended reading is K1UHF's article in QST, October 2003, about using 
sound cards:
http://www.westmountainradio.com/pdf/Ins&Outs.pdf

K1UHF's article has a further link to:
www.barberdsp.com/tech/cs100.pdf
This article is about a specific audio software product, but the section 
titled 'Is my sound card good enough?' has some interesting information.

Both authors make the point that it's much better to use the Line Input 
jack rather than the Mic input. Not all of the cheap PCI cards or 
onboard sound systems have a separate Line Input jack, so this is a 
feature to check when choosing a cheap card (although you can still use 
the Mic input instead, with the 20dB boost switched OFF).


BTW, I bought two of those Turtle Beach Santa Cruz cards from Ebay, that 
were being discussed here a couple of months ago. I was well satisfied 
with the deal, because you can't buy them at anything like that price in 
Britain (100% satisfaction about the vendor also). But they certainly 
won't be going into the radio PC!


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek