[RTTY] TinyFSK modem for 45 and 75 baud

[Joe Subich, W4TV]

On 10/11/2013 9:52 AM, Jim W7RY wrote:
 > So which is it?  EXT FSK or hardware?

I don't understand the question.  Traditional serial ports - even the
internal expansion cards and the Edgeport devices work just fine with
no special drivers.  microHAM's "Keyer" products do stable FSK timing
at any of the amateur speeds with a UART based software interface.

In addition to Andy's solution, one could also use a USB to parallel
interface with an externally clocked shift register (parallel to
serial converter) with custom drivers.  Finally, Andy's hardware could
be made to emulate a UART by using the FTDI D2XX (DLL) drivers and a
custom virtual serial port front end (e.g., Eltima's VSPAX) which is
essentially the process used in the microHAM "keyer" products (they
are also ATMega devices with an FTDI USB port).

73,

    ... Joe, W4TV


On 10/11/2013 9:52 AM, Jim W7RY wrote:
> 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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