[RTTY] Audio Card Reccomendations

[Kok Chen]

On Mar 8, 2009, at 5:27 PM, Jim Rhodes wrote:

> From the look of the thing on their web site, it does not do FSK.   
> Is that right Darl? I kind of liked the look of it till I couldn't see
> anything about FSK.
>
> At 08:52 AM 3/8/2009, Darl Deeds wrote:
>> I just use a Signal Link which has an audio card as part of it.

The SignaLink USB is a USB based sound card that comes with a VOX  
mechanism which will trigger a PTT keying line for you when the  
computer sends AFSK tones to it.  In spite of the fact that it  
contains a USB port, there is no way to send a "hard" PTT to it, nor  
can you use it to key an FSK transmitter.

Because it uses VOX, it will only work with full duty cycle (e.g.,  
RTTY, MFSK16) modes, or near full-duty cycle (e.g., PSK31) modes --  
its PTT is too slow to work with J2A.  For RTTY, you need to make sure  
that your software puts out a sufficiently long steady mark tone at  
the start of a transmission to engage the VOX before you begin sending  
the first character or diddle, otherwise the first couple of  
characters may not be correctly decoded at the receiving end.

In addition to the transformer for the transmit audio, it only has one  
transformer for the receive audio and therefore does not completely  
support rigs that have two receivers if your software supports  
multiple receivers.

Since the Burr-Brown codec chip that it uses has no software  
adjustable input attenuators (the Burr Brown PCM-2902 has neither  
master level nor independent left/right level attenuators) and the  
SignalLink's level pots are printed circuit mounted trimpots inside  
its box, there is no way for you to "ride the gain" between weak DX  
and strong signals.

There is a problem with this particular Burr-Brown codec when used  
with Windows XP and Mac OS X (Intel) at 11025 s/s and 44100 s/s  
sampling rates; and you will be restricted to certain sampling rates  
that do work, such as 12000 s/s or 16000 s/s (i.e, something that  
evenly divides 96,000,000).

If you can live with the above constraints, the SignaLink USB is a  
very simple "plug-and-play" device for first time digital mode  
operators.

Vy 73
Chen