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[aprssig] desirable laptop computer features?

Stephen H. Smith wa8lmf2 at aol.com
Tue Oct 31 21:31:21 UTC 2006


gregg at wonderly.org wrote:
> Dale Blanchard wrote:
>> Stephen H. Smith wrote:
>>
>>> etc.
>>> Unfortunately, virtually NO consumer mass-market laptops have serial 
>>> ports anymore. You will have to go to higher-priced business and 
>>> specialty-market machines to get real ports.  (This is why I just 
>>> paid USD $1500 for a new Panasonic Toughbook CF-51 15" CoreDuo 
>>> laptop through a specialty reseller,  instead of buying a similar 
>>> consumer market machine for under $1000.)  
>
> I don't really think this is as big of an issue as some make it out to 
> be.  It really depends on the software that you are using, which 
> USB->Serial adapter you get, and then how you can configure that 
> adapter based on the manufactures software support for "setting" the 
> comm port.  The keyspan devices, as has been mentioned here before, 
> seem to be the best choice.
>
> Stephen, I think you've discussed using the keyspan devices before.  
> Can you share more about your need for a real port?
>

I've never used the Keyspan devices but have used a variety of other 
devices.   From my experiences:

1)   Many drivers try to configure themselves at COM5 or higher.   This 
presents a problem with many legacy programs that only offer the classic 
COM1 through COM4 that DOS knew.    For example the "Memory Control 
Programs" for configuring and saving the memory channels of various 
Kenwood radios. Many GPS config or monitor utilities. Or even the 
programming utiltiies provided by the landmobile radio manufacturer 
formerly known as GE that TO THIS DAY distributes DOS-BASED programming 
utilities for their latest and greatest P25 digital radios!

If the the USB dongle's driver does let you force it onto a lower legacy 
COM number, you will often find that  serial-portless laptops have 
already "commandeered"  COM1 through COM4 for modems, serial IR links, 
bluetooth virtual serial ports, cell phone and PDA programming links, 
etc.   

Note also that while the COM selectability is usually present in Win XP 
drivers, it almost never is in Win 98 drivers and may  or may not be in 
Win 2K drivers.



2)   Incompatible with non-standard baud rates and word lengths.  Many 
dongles won't work at 110 baud (for ASCII  RTTY applications) or 45 baud 
5-bit BAUDOT code for "classic" RTTY operation. A surprising number of 
them will only do the standard baud rates that are powers of two 
starting at 300.



3)   Non-constant latency in the USB-to-serial or serial-to-USB 
conversion.   This is not usually a problem when the handshake lines are 
merely controlling the flow of bytes into/out of the serial port UART.   
However many ham apps use the handshake lines in unorthodox ways.    The 
simple soft-modem applications for RTTY and SSTV that feed clipped and 
limited receive audio into the handshake line of a serial port for 
pulse-count demodulation usually won't work with the dongles.  The 
delays for the state change, from the serial port pin to the USB side to 
back to a virtual COM port inside the PC are non-constant, screwing up 
the demodulation by counting microseconds between zero crossings. 

On  the transmit side, some applications wiggle a single outgoing serial 
port handshake line to directly key the FSK input on some HF 
transceivers for  sending classic RTTY, or to send CW by connecting an 
open collector transistor across the radio's CW key jack.  Again, the 
variable latency of the program-to-USB-to-serial conversions make it 
difficult or impossble to reconstruct a precisely-timed 45.45 baud RTTY 
FSK rate or precisely formed CW characters.



4)    Windows absolutely maddening "plug-and-pray".   Many times I have 
had the experience of having Windows automatically DE-INSTALL the driver 
for a particular USB device if the machine was booted several times 
without the device being present.  Then when you DO connect the device 
on a subsequent boot, Windows stupidly acts as though this is a 
brand-new   never-before-seen    device and prompts you through the 
whole driver install drill AGAIN, nagging you for the "manufacturer's 
CD".  Yes, you can usually tell it to look somewhere in the /WINDOWS or 
/WINDOWS/SYSTEM32 directories for the driver, but it's a pain in the 
neck, especially if you are booting a mobile computer and just want to 
get underway in a hurry.






--

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


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