OK - I think I have a complete explanation of what this is all about.
Here goes:
1) The problem is not really a problem, but rather a feature of most serial
ports, which is an holdover from the early days. The UART (universal
asynchronous receiver-transmitter) device that is part of the serial port can
produce properly timed RTTY characters on it's output, which is the TXD of the
serial port.
2) Newer devices, most notably, USB to serial convertors, do not have this
"old" functionality. I understand that Belkin USB to serial devices may be an
exception to this and have a UART in them. The reason this has changed, is
that this 5 bit capability is only run at 45 baud, and these new devices are
engineered to go so much faster than that, that they have left this capability
out as unnecessary. No one uses 5 bit baudot code any more - right?
3) The input to a radio - the RTTY jack - is a simple input that receives a
logical off or on, open or closed, a 0 or a 1. It does not receive the 5 bit
"data", but instead receives logical open or closed input that follows the
changes in state that produce the 5 bit baudot code. There is no conversion of
the data going on in the radio. If the RTTY input is left open, the carrier is
output on the Mark frequency. When the RTTY input is shorted, the frequency of
the transmitter shifts by 170 Hz. This is all that happens. Open - the
transmitter is on the Mark Frequency; closed - the radio shifts the transmitted
carrier to the Space Frequency offset.
4) The UART in the serial port converts the 5 bit code - not the radio. You
could just connect a momentary pushbutton to the RTTY jack on your radio, and
it might be possible that you could produce 5 bit baudot FSK output from your
radio. The timing is critical enough that you probably cannot communicate with
someone else.
5) It would be possible to use the DTR output of the serial port to provide the
logic necessary for driving the radio's RTTY input - if the functionality of
the UART was emulated in software. However, the approach is to use the UART
since it already has this capability. Sort of a "why re-invent the wheel"
approach. The other school of thought would be to move this to some other
external device rather than doing it in software. We may see new devices that
will provide this capability in the near future.
Summary:
The reason that I wanted to get to the bottom of this, is that I wanted to
understand why we had to sacrifice the radio control capabilities of a serial
port in order to produce a simple switch closure to drive the radio's RTTY
input. The reason is because the UART has the intelligence to convert the
letters and characters to the precisely spaced output which can only be
produced on the TXD output of the serial port. It seemed logical to me (prior
to knowing about the UART stuff) to seek to use the DTR output (CW normally)
instead, as it is not used during RTTY operation.
For the time being, if you want to control your radio, and you want to run FSK,
you will need 2 serial ports. However, you can use any of the USB serial ports
to control your radio, and use the built-in serial port (which likely has a
UART) to do the FSK stuff.
I am now doing this with one of the Microham USB devices to do CW, PTT and
radio control, and the serial port on my computer to do the FSK.
73,
Bob N5NJ
> ------------Original Message------------
> From: Bob Naumann - N5NJ <n5nj@gte.net>
> To: "Nick Kail" <m3mlr@tiscali.co.uk>, "'FireBrick'" <w9ol@billnjudy.com>,
> "'Writelog List'" <writelog@contesting.com>, "'FT1000MP List'"
> <1000mp@mailman.qth.net>
> Date: Fri, Feb-27-2004 10:43 AM
> Subject: Re: RE: [WriteLog] microHAM USB interface
>
> Can someone explain the 5 bit "problem"?
>
> Why couldn't the CW output just be hooked up to the FSK connection on the
> radio? Is that connection on the serial port just not capable of switching
> fast enough to do rtty?
>
> -N5NJ
>
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