Getting Started on RTTY - Page 8
Specifics - Serial port pinouts, USB-to-Serial Adapters & EXTFSK
There are a few things I didn't cover on the other pages
which are good to know, but not necessary to understand in order to get started
on RTTY. These things are specifics which might help you grasp certain concepts
better or help in troubleshooting RTTY problems. There is also information
on USB adapters and using EXTFSK on this page. EXTFSK is required to key
PTT and/or FSK from a parallel port AND when using a USB-to-serial port adapter.
It also has other nice features like allowing FSK transmission from RS-232
outputs other than TxD.
Serial Interface Pinouts
While covering PTT and FSK interfaces, I showed a diagram of a simple transistor
circuit connected to pin 7 of a 9 pin serial port for PTT. However, I didn't
mention that this pin is specified as RTS (Request To Send). It just happens
that pin 4 (DTR - Data Terminal Ready) on a 9 pin serial port does the exact
same thing and could be used in place of pin 7 (RTS). It doesn't really matter
if you use RTS or DTR, but you might want to know this if you are trying to
install jumpers in a RIGblaster Plus or trying to understand why some PTT
interfaces use Pin 7 while others use Pin 4 on a DB 9 connector.
Likewise, I failed to mention pin 3 of a 9 pin serial port, the one used for
FSK, is called TxD (Transmit Data). You really don't need to know this either,
but don't you feel better now that you do?
And because most computers today use 9 pin serial ports, I failed to tell you
what pins would be used for a 25 pin serial port. RTS is pin 4, DTR is pin 20
and TxD is pin 2 on a 25 pin serial port.
Why can't you just connect your radio straight to these pins on your serial
port? Because some of the pins will vary in voltage from +12v to -12v
(RS-232 voltage levels) and your radio may not be able handle that. Your radio's PTT
circuit is looking for a ground to key the circuit and turn on the
transmitter. Your FSK circuit is looking for either an open or a ground to
shift the frequency of the radio. Although some operators have had success
directly connecting the TxD line straight to the FSK input of their
transceivers, I do not recommend this. Thus you need an interface circuit.
USB-to-Serial Adapters
MMTTY has provisions for altering the polling rate and speed on a USB port for
use with a USB-to-Serial adapter when using such a device to run FSK. However,
only one USB adapter, the Belkin F5U103, will run 5-bit Baudot code. The
most successful way to use a USB-to-Serial port adapter is to use EXTFSK. An extension to MMTTY
is available called EXTFSK that can be used to control serial, parallel and USB
ports. See the EXTFSK discussion in the next section on this page.
The problem with USB adapters is the UART used in nearly all adapters today do
not support 5-bit data and will not work for FSK transmission. I have used
the Belkin F5U103 to run FSK and it worked with no problems under Windows 98.
However, I could never get my F5U103 to run under Windows XP. Some
operators claim to have installed their F5U103 adapter under Windows XP, but
I've not had their success. Forget about trying to key directly with the
USB-to-Serial adapter without using EXTFSK. Use EXTFSK!
The Microham USB microKEYER successfully keys FSK via the USB port when used with MMTTY and the MMTTY plug-in for WriteLog. I have tested the Microham USB microKEYER and reported my results on my rttycontesting.com web site. For the Microham pages, click here.
To get to the USB Port Options within MMTTY, go to Options, Setup MMTTY and to the MISC tab. Next to the COM-TxD FSK) option, there is a button that, when pressed, brings up the USB Port Option window.
When the USB Port Option window appears, there are four options to choose from. I used option C: to get my F5U103 to work. Try each of the options to determine if any of them will work.
Using EXTFSK
EXTFSK.DLL is an additional driver that can be added to MMTTY which allows software control of FSK and PTT keying on serial, parallel and USB-to-serial port adapters. Normally, these functions have been controlled by the hardware UART for the serial port or USB adapter. What this means is that it's now possible to key FSK and PTT on a parallel port as well as changing which pins control FSK and PTT on a serial port. With EXTFSK, you can key PTT and FSK on DTR, RTS or TXD on the serial port. The only stipulation is that you can't use the same pin to key both!
By using EXTFSK, it may also be possible to allow USB-to-Serial adapters work for FSK and PTT which would not work under the normal MMTTY setup described earlier. EXTFSK is available from MMTTY page of the MM Hamsoft web site. EXTFSK is contained in the comfsk105.zip file along with the source code and readme.txt file. To use EXTFSK, download comfsk105.zip, unzip it and place EXTFSK.DLL in the same directory as MMTTY.EXE. The readme.txt file contains the information needed to use EXTFSK.DLL.
To activate EXTFSK once EXTFSK.DLL has been placed in the MMTTY directory, first go to the TX tab in MMTTY Setup and select EXTFSK in the PTT Port pull-down window (remember this Port selection is for both PTT and FSK).
If EXTFSK is not showing in the Port pull-down menu, then EXTFSK was not properly placed in the same directory as MMTTY.EXE. After EXTFSK has been selected, go to the MISC tab and select either FSK Tx port option and press the USB button. Select A: Normal and hit OK. Back at the TX tab, hit OK again and the EXTFSK window will appear separately from the MMTTY window. In this window, you can select which COM or LPT port you which to configure. In order to use an LPT port, you must first install DLPORTIO. DLPORTIO installation is covered in the readme.txt file. Additional support on using EXTFSK to key FSK on a parallel port can be found at http://www.g4zfe.com/rtty.html.
I have tested EXTFSK with a Keyspan USB adapter and it worked fine. I've not tested EXTFSK to key FSK on a parallel port , but I do know that others have had success in keying FSK & PTT from a parallel port under Windows 2000 and XP. This is important for those laptop computers that do not have a serial port. You can also change which pins control FSK & PTT on a serial or parallel port. Some sort of interface to convert the control voltages to on/off keying is still needed in most cases.
For WriteLog users, EXTFSK is not available when using the MMTTY plug-in to WriteLog. However, WriteLog allows FSK keying via a USB adapter when using the "Software generated FSK" option under the Port menu in the Rttyrite window.