[RTTY] TinyFSK modem for 45 and 75 baud

[Jim W7RY]

So which is it?  EXT FSK or hardware?

73
Jim W7RY

On 10/11/2013 6:44 AM, Joe Subich, W4TV wrote:
>
>> However, many people use standard consumer-grade USB-Serial
>> converters without true UARTs and they therefore require the EXTFSK
>> optional module for MMTTY to provide correct Serial timing.
>
> Not quite correct ... most of the commercial USB-Serial converters
> are true UARTs.  The problem is that the chip foundries have increased
> the internal clock speeds in order to operate at higher data rates for
> mass storage applications, processor interfacing, etc.
>
> These higher maximum data rates create a problem because of a fixed
> ratio of the maximum to minimum data rate.  UART data rates are set
> by a 14 bit "data rate divisor" which means (other than certain
> special cases) the maximum rate can't be more than 2^14 (16,384) times
> the lowest supported rate.  As the USB specification has expanded to
> support ever higher data rates and equipment designers have demanded
> hardware support (e.g., transfer 64 GB of data to/from a camera,
> MP3 player, phone, tablet by USB) for faster data rates, the chip
> fabricators have been forced to abandon support for the "obsolete"
> data rates.  Most new USB UARTs are now limited to 300 baud minimum
> and I don't know of any designs introduced since the advent of the
> USB 2.0 standards that support a minimum data rate rate less than
> 110 baud.
>
> 73,
>
>    ... Joe, W4TV
>
>
> On 10/11/2013 3:00 AM, Ed Muns wrote:
>> Nothing ... IF your computer has real, i.e., with good UARTs, hardware
>> serial ports., or you use a USB-Serial converter such as the Edgeport 
>> units
>> with real UART components.  However, many people use standard 
>> consumer-grade
>> USB-Serial converters without true UARTs and they therefore require the
>> EXTFSK optional module for MMTTY to provide correct Serial timing.  
>> Turns
>> out that MMTTY's EXTFSK's "correct Serial timing" is not so correct.  
>> Thus,
>> a solution like Andy's is warranted to obtain perfect RTTY timing via 
>> USB.
>>
>> The Edgeport converters are commercial products retailing for over 
>> $300, but
>> I've bought lots of them for $30 or less (4-port) and $60 or less 
>> (8-port)
>> on eBay.  Just two different approaches to obtain proper Serial timing.
>>
>> Ed W0YK
>>
>> Andy K0SM/2 wrote:
>>>> For those of you looking for a relatively simple and
>>> inexpensive method of doing 45 and 75 baud RTTY using logical
>>> keying ("FSK") you can have a look at a TX-only modem that I
>>> built that will accomplish this.
>>
>> Bill W6WRT wrote:
>>>
>>> REPLY:
>>>
>>> What does this do that MMTTY and a pair of one-transistor
>>> drivers for FSK and PTT does not do?
>>
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