[RTTY] Fldigi Question]

[Ed]

-------- Original Message --------
Subject: Re: [RTTY] Fldigi Question
Date: Thu, 29 Jan 2009 19:47:04 -0500
From: Ed <w3nr at comcast.net>


Kok Chen wrote:
> On Jan 29, 2009, at 1/29    7:56 AM, Lee Buller wrote:
> 
>> I've tried to glean through the documentation, but does Fldigi  
>> support devices like SignaLink USB?
> 
> It should work.  There is really no issue in the SignaLink USB a  
> software modem has to specifically address.
> 
> All the SignaLink has is a 16-bit sound card (using a Burr Brown chip  
> from the PCM2902 chip set), a couple of transformers (one in, one  
> out), pots for level control, and a VOX circuit to generate PTT (what  
> microHAM calls "auto PTT," but only available on the microKeyer II as  
> far as I can tell).
> 
> The only connection you need to make from the computer is to the USB  
> sound card.  And you don't need a special drivers when used with  
> Windows and Mac OS X since the Burr-Brown is USB audio class  
> compliant.  I suspect that is true with Linux, also.


The same is true of Linux as well as BSD. The chip is supported in all
current Linux kernels.



> You didn't say which operating system you are using fldigi on.  But  
> there could be issues that are not fldigi specific, but specific to  
> the PCM2902 and the underlying operating system (you didn't say if  
> you are running it on Windows, Linux or Mac OS X).


There have been no problems with the Signalink ony any platform. However
fldigi will not run on Win 95/98. Nor does it like less than a 700Mhz
machine.



> The thing you need to be careful of when using the Burr-Brown, ergo  
> the SignaLink USB, in Windows is that you need to select sampling  
> rates that evenly divides 96000000.  I.e., don't choose 11025 s/s or  
> 44100 s/s sampling rates, or your transmit frequency might not zero  
> beat to your receive signal (no kidding!)  Choose something like  
> 12000 or 16000 or 32000 s/s instead.


I would suspect that 48000 is the native samplerate for this. There were
problems with noise on some cards that were tested and required setting
the samplerate as Chen suggested. 11025 is a definite no-no.



> Mac OS X modems that uses Core Audio does not have this frequency  
> discrepancy since Core Audio resamples audio to the internal clock of  
> the computer based upon time stamps.
> 
> However, on the Intel version of Mac OS X, has a much worse problem  
> if you choose 11025 or 44100 s/s with the Burr-Brown PCM2902.  So you  
> also need to use 16000 or 32000 s/s if you are on an Intel based Core  
> Audio modem software.
> 
> fldigi does not use Core Audio, so it does not have that problem on  
> Mac OS -- but to be safe, use 16000 or 32000 s/s when you use a Burr- 
> Brown codec sound card such as the SignaLink.  You can identify them  
> by the PCM2902's USB PID/VID.  You should be able to Google for the  
> PID/VID of that codec.


It is suggested to calibrate the sound card (highly recommended) and
fldigi has a built-in WWV modem to do this. It is well documented in the
help files. fldigi supports /dev/dsp, portaudio, and pulseaudio.



> 73
> Chen, W7AY


I always enjoy reading Chen's dissertations. He is a man of remarkable
knowledge.

73

Ed W3NR

alpha tester: fldigi