[UK-CONTEST] Data contests

[Andy Swiffin]

>>> On 22/01/2011 at 10:36, in message <4D3AB33D.9090105 at btinternet.com>, David
G3YYD <g3yyd at btinternet.com> wrote:
> 
> On the sound card settings do not use 11025Hz sampling rate as modern 
> sound cards will not provide an accurate rate. It is better to use 
> 12000Hz. Modern sound card sample at 48KHz or integer multiples of 
> 48KHz. The driver software then converts the 48KHz to the requested 
> speed. As a result 12KHz is easy to do by sending every 4th sample to 
> the decoding software. Generating 11025 from such a card will result in 
> a compromise rate, which could be significantly different. This does 
> result in TX/RX baud rate being incorrect along with the received tone. 
> If using FSK this can mean you call people off frequency another reason 
> for using AFSK rather than FSK.
> 
> The baud rate setting should be 45.45 and not 45.


Hi
I've been doing a little investigation on this and submit my findings in case other people might be concerned.

I use the default 11025hz sampling rate on mmtty (+n1mm) on my laptop.  I was a bit concerned about the above even though I've generally noticed when running in contests that people do seem to call me back dead on frequency.

I did a few tests on the bands, calling CQ and seeing where people called me,   they all seemed to be right on my frequency (including one nice chat with well known rttyer Mike K4GMH who certainly knows what hes doing).

So, certainly in my case on my laptop,  11025 doesn't seem to present any problem with a frequency offset between using FSK for transmit and the audio coming in for receive.  

I'm posting this in case anyone else is thinking they might have to change settings to get this right,  I certainly don't have to.

David - do you have any references to the information you post above,   I did some google searches, but couldn't come up with anything?

73
Andy 
gm8oeg






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