[RTTY] 45 baud

[Kok Chen]

On Nov 8, 2011, at 5:03 AM, Jim McDonald wrote:

> Since MMTTY has both 45 and 45.45 baud rates, I was curious whether my HAL
> DXP38 was using 45 or the precise 45.45 baud rate, so I asked Joe K9SZ at
> HAL.

The manual for my HAL DSP-4100 says "45 baud," but I had always suspected that they meant 45.45 baud.  Since HAL also caters to the commercial market, I had always believed that the HAL modems did the correct thing when it comes to baud rates.  

The one FSK hardware interface I know of which you can only select 45.0 baud is not manufactured by HAL.  With that particular family of interfaces, the FSK baud rate is determined by 2700/n where n is some integer division factor.  Ergo, 45.45 baud is not possible.

Indeed, it is better to us a division factor of 49 with that interface and select 45.76 baud, which is closer to 45.45, than to use a division ratio of 60 which gives 45.0.

Anyhow, IMHO the difference between 45.0 and 45.45 is small enough to practically ignore.  Don't lose sleep because of it (let silly guys like myself lose the sleep over factions of dB here and there :-).

Switching between 45 and 50 baud is a different story, which most people know about from the P5/4L4FN experience.  The 45 vs 45.45 problem also pales in comparison with the problem of using something like EXTFSK.  Unfortunately, the transmit baud rate losses only affect your FSK transmit signal and many people don't even realize that their signal is a little noisier to copy because of it.

73
Chen, W7AY