[aprssig] Re: Serial port to USB question

Stephen H. Smith wa8lmf2 at aol.com
Sat Sep 3 21:19:56 CDT 2005

victorf at windreader.com wrote:

> *I am attempting to connect my D700 to APRSPoint. I have a 'modern' 
> Dell laptop sans serial ports. I can attach the TNC output to a USB 
> port using a Belkin Serial => USB converter and can see the APRS 
> packets streaming into a terminal program - 9600Baud, 8N1. So I am 
> sure the converter is working and the comport selection matches what 
> is found in the Windows XP Device table (com4 in this case). However 
> attaching in EXACTLY the same way to APRSPoint and setting the TNC 
> port as above does not work. I get the error message "TNC not 
> detected". I have MapPoint 2004 installed and am using AP 2.1 for MP 
> 2004. I AM a registered user of both MP and AP.*
> **

Serial-to-USB converter "dongles" vary wildly in how faithfully they 
emulate a real serial port.  Especially how they emulate (or don't 
emulate!) the hand-shaking lines of a real serial port since these lines 
don't exist in USB. Some will work only with some programs, others with 
nearly all.   The Belkin converters are especially notorious for poor 
compatibility and have been repeatedly blasted on this list,  the UIview 
mailing list and the MixW list.    

Some of the variables involved are: 
o     What IC chipset is the cable based on? 
o     What IC chipset is used for the USB ports on the PC? 
o     Are the PC's ports USB 1.1 or 2.0? 
o     Are you going directly into a PC's USB "root port" or through a 
USB hub or splitter?
o     What operating system (Win 98SE, Win2K or WinXP) are you using?
o     What patch or service pack level is your OS at?
o     How many other USB devices are in use at the same time?
o     Does the application depend on accurate handshaking or does it 
only require the basic RXD/TXD/Gnd three-wire serial hookup?  [This 
often drives sound-card-interface users to despair since the serial 
port's handshaking lines are used for Radio PTT, CW keying, Receiver 
squelch detect, etc. ]

The Edgeport converters have frequently been commended as being among 
the most trouble free on the UIview list.   I have personally used SIIG 
and pFranc/Purple Computing cables with my D700 and TH-D7.  

The Purple Computing (actually MCT Technology) cable works successfully 
to connect my D700 to UIview, APRSplus and APRSpoint, or to feed a GPS 
into Delorme Street Atlas or Precision Mapping 6.0  or 7.0.  However it 
ABSOLUTELY WON'T WORK to feed a GPS directly into MapPoint 2002 or 
2004.  (The Microsoft web site even confirms that MapPoint will only 
work with "real" serial ports!).  

[Note that I am referrring here to feeding a GPS directly into MapPoint 
for a moving map display of my own location; not using an APRS 
application. I am only citing it here to illustrate how inconsistent the 
behavior of these devices are, and to illustrate  that "because it 
worked with app A but doesn't work with B" doesn't prove there is 
anything wrong with your setup.  ]

The SIIG dual serial-to-USB works perfectly on everything I threw at it 
on a PC with only USB 1.1 ports, but only works on another similar 
machine with USB 2.0 ports with only about 2/3rds of the 
programs/hardware tested.  

A no-name generic cable with a DB9 encapsulated in transparent "Imac 
blue" plastic that is based on the FTDI chipset, has worked flawlessly 
for 12 months 24/7 nonstop connecting a KPC3+ TNC to my APRN / 
HF-VHF-APRS / Echolink "Ham Superserver" based on a Via EPIA-TC 

On a 1.6 GHz P4 Centrino laptop (i.e. recent machine about 9 months old 
with native USB 2.0 ports) running Windows 2K, a USB-interfaced Holux 
GPS mouse will not work with MapPoint directly (It will with Streets & 
Trips!) , but WILL work if I have Franson GPS Gate (a utility that 
intercepts data from a GPS on a single serial port and shares it with 
several programs at the same time) in between the virtual serial port 
and the application.   
     [The Holux, like all "USB" GPS devices, is actually a serial device 
with a built-in serial-to-USB converter chip. These converters are 
identical to the ones used in stand-alone serial-to-USB converter 
cables.  In fact the Holux uses the identical chip and driver as the 
pFranc/Purple Computing cable.  Thus the same random compatibiliy issues 
prevail. ]

Bottom line:

You will have to experiment with several different USB-to-serial dongles 
to find one that works with your particular hardware and OS revision.    

Note further that the chronic random instability of Windows 
"Plug-and-Pray" auto-configuration will cause some of these converters 
to assign themselves a different virtual COM port number on successive 
boots.   Some of the better drivers for Win2K and XP give you an option, 
in the Windows Device Manager, to assign and lock down the COM port 

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

"APRS 101"  Explanation of APRS Path Selection & Digipeating

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