WA8LMF Home Page | Main Ham Page | Main APRS Page | Updated 24 June 2014  


USB-to-Serial Adapter Cables for Ham Applications

Introduction | Prolific 2303 Problems | The Ultimate Dongle ??

For over 15 years now, Microsoft has been attempting to force the phase out of classic RS-232 serial ports on PCs.  (They actually coined the term "Legacy-Free PC" to refer to new designs without serial or parallel ports.)   

However, many , many amateur radio applications still require RS-232 serial "COM" ports. Some of the many uses are: packet TNCs, radio memory programming, connecting GPS receivers, sound-card-interface transmit keying (PTT), rotator controls for satellite tracking, and remote control & logging applications on HF transceivers.

Virtually no new PCs available at retail for the last 5 years have serial ports. Serial ports are still available on some expensive specialized machines intended for non-consumer use, such as Panasonic Toughbooks and certain vertical-market Dells.  The majority of "civilian" users have been forced to resort to the notorious and frequently problematic serial<-->USB converter cables a.k.a. "dongles" if serial ports are required. 

These cables are not just pieces of wire with a different kind of plug on each end. They actually contain an active microcontroller device, . One of a half-dozen or so specialized serial/USB conversion chips, provided by one of 4 or 5 manufacturers is inside the molded DB9 plug, powered from the 5 VDC available from the USB end. In turn, this chip is dependent on a software driver installed into the operating system to function. Normally, such drivers create a virtual COM port that serial-using applications can then use like an actual physical serial port.

The quality and stability of the drivers varies wildly from chip vendor to chip vendor.  Some versions of these drivers emulate a physical serial port far more faithfully than others.  Some drivers will work with certain versions of Windows but not others. Or only certain applications will recognize the virtual COM port created by the driver.


Further, users may be dealing with the headaches of serial<-->USB conversion without even realizing it.  So-called USB GPSs, USB interfaces on transceivers, "USB" versions of TNCs and other devices are actually serial internally.   Exactly the same kind of serial<-->USB chip as in the stand-alone cables, is used to offer a "USB" version of the device.  The only difference is that the serial<-->USB conversion takes place inside the device rather than in a cable between the device and the computer. Many of these so-called USB devices use exactly the same chips and drivers as the stand-alone serial<-->USB cables.  

The give-away is that the applications on the PC, that use these devices, still require you to choose a COM port rather than referring to the USB device natively by name. 

For example, the "USB" interface on the Kenwood TH-D72 APRS handheld is actually the serial interface of it's predecessor TH-D7 with a serial<-->USB chip added internally.  The "driver" provided for the PC reconstitutes the serial COM port of it's predecessor for the benefit of APRS and packet programs that only think in terms of classic RS-232 COM ports.   The ultimate irony is that the radio-specific memory programming utility for this "USB" radio requires you to choose and access a virtual COM port, instead of natively accessing the USB port.

A second example. The USB-based "GPS Locator" bundled with some versions of Microsoft Streets & Trips, MapPoint & Autoroute, the Globalsat BU-353 low-cost puck GPS, the Pharos iGPS-180, many Holux GM-series GPSs, and countless other GPS devices are all based on the Prolific PL-2303 chip. They use exactly the same driver for the Prolific PL-2303 chip that you find bundled with countless low-cost serial<-->USB dongles.   The only difference is that the device description (that shows in the Windows Device Manager) has been changed from the generic "USB-serial Bridge" to "Microsoft GPS Locator" or something similar.


The Major Problems with the Prolific PL-2303 Chip and it's Drivers

One of the most widely-used chips in low-cost serial<-->USB dongles and "USB" GPS devices is the Prolific Technology PL-2303.   It's drivers have been released in countless versions for every flavor of Windows beginning with Windows 95/98 up to and including the latest Windows 8-64.  This device has also been supported on various flavors of Linux, the Mac OS and even on Android smart phones.  Prolific's English-language home page in Taiwan is here:


This device and it's associated drivers worked reasonably well until manufacturers on the Chinese mainland began counterfeiting Prolific chips several years ago, and started pirating Prolific's drivers.   Prolific responded by placing a kind of DRM (Digital Rights Management) into it's drivers. The driver somehow tests the chip for "authenticity" and refuses to run if the chip is deemed a fake. This yields the dreaded yellow triangle with exclamation mark in Windows, along with "Error Code 10 - Failed to install driver". 

The fake 2303 chips have managed to infiltrate the world-wide electronics-manufacturing supply chain, and randomly appear in hundreds of products from dozens of legitimate manufacturers.  Many manufacturers of GPS devices and serial<-->USB dongles have taken to bundling older versions of the Prolific driver (that lack the "genuine check" routine) with their products to work around this headache.    However these older drivers often won't work with newer variants of the PL-2303 chip.  Since many different devices use the PL-2303 chip, you experience some version of the following scenario:

Or everything worked great on your old Windows XP computer, but now nothing (or only some devices) work(s) on the new Windows 7-64 computer

Some manufacturers bundle new driver versions that have been hacked to disable the "genuine check".  These work on 32-bit versions of Windows XP and Win 7.  However, they fail miserably on Windows 7 & 8 64-bit editions.  This is because the 64-bit editions of these OSes require drivers to be tested, certified and blessed by Microsoft with a "digital signature" before they will install.  The "hacked" versions of the driver fails the digital signing validation and won't install on 64-bit systems.

Or you can go through a byzantine procedure involving registry hacks and reboots into "Safe mode" that defeats driver signing tests in Win 7-64. (There is a "Test" mode, intended for developers of new drivers, that will defeat the driver signing test and allow the installation of "unofficial" drivers for testing and debugging.)   

After the "test mode" tweaks, the hacked driver works for a while....   until the ever-helpful Windows Update decides to automatically download and install the latest official Microsoft "signed" version of the PL2303 driver that DOES include the "genuine" check in it.

There are really only two ways to get around this mess.

This May Be The Ultimate Dongle For Ham Applications!

Serial<-->USB interfaces based on the FTDI chip set do not suffer from the numerous problematic driver issues that plague the Prolific chipset.  There are numerous serial<-->USB devices based on the FTDI chipset, but the one pictured below, a "Gearmo FTDI2X" is exceptionally useful for ham applications.

Typical Serial Port Configuration Dialog

FTDI Expanded Serial Options

This product is made by "Gearmo".   Their website is here:


Note that they offer a variety of FTDI-based dongles in versions with 1, 2 or 4 serial ports from one USB port. They sell through the website. 


I got mine for USD $10 less from this Amazon page:


Update  22 May 2013:  Apparently the writeup on this page has already caused a sellout of the limited supply of the Gearmo cables at the cheap price this vendor had!   Hope that they restock.


A version with a single serial port on a short (less than 1 foot) pigtail is here:


Googling for "ftdi usb to serial" yields quite a few other dongles based on this superior chipset, which should have about the same capabilities.

    From NewEgg

    Another (single port) Gearmo from Amazon

    Even Walmart