Running VAC 4.09 on Vista & Win7 x64 (64-bit)

Running VAC 4.09  on Vista & Win7 x64 (64-bit)

  System Dependencies
  Minimum PowerSDR Version:     N/A  
  Applicable Hardware:     All transceivers  

Content provided by: FlexRadio Systems Engineering

Virtual Audio Cable, more commonly referred to as VAC is a third-party software package that facilitates digital audio transfer between PowerSDR and other sound card enabled programs, like most digital mode programs (MixW, Digipan, MMTTY, etc.).  VAC is able to do this because it is a kernel mode Windows device driver that emulates a sound card.

NOTE: VAC is a third-party software program and is not directly supported by FlexRadio Systems.  FlexRadio Systems recommends its use with PowerSDR to facilitate digital audio transfer (DAX) between other third-party sound card programs.  All inquiries in regard to the basic operation of VAC or concerns regarding it being unsigned (see below) must be directed to the VAC developers ( themselves.

Windows Vista and Win7 come in two basic configurations; 32-bit or x86 and 64-bit or x64.  A Windows device driver has to be the same "bit size" as the operating system, so a 32-bit operating system can only use 32-bit device drivers and 64-bit operating systems can only use 64-bit device drivers.  VAC comes in both a 32 and 64-bit version, so from a driver architecture standpoint, VAC can operate on both 32-bit and 64-bit Windows operating systems.

With the introduction of Vista x64 and continued on with Win7, Microsoft imposed another requirement for 64-bit device drivers.  They require all 64-bit kernel mode drivers to be signed with a digital signature in order to operate normally.  VAC is not a signed driver, therefore special boot time operations must occur for the driver to load under Vista x64.

Please refer below to the information about running the unsigned VAC device driver under Vista/Win7 x64 as taken directly from the VAC Help file (vac.chm) documentation included with the VAC application.

From the VAC Installation Guide in the Application's Help System
Under 64-bit Vista, kernel-mode drivers require a publisher's digital signature to be loaded. VAC is not signed due to Microsoft's security policy that does not allow an individual developer to obtain a publisher certificate. Even the installation completes successfully, 64-bit Vista displays a warning and does not load the driver. Unsigned drivers can be loaded in the "test modes" only. Please read "Installing an Unsigned Driver During Development and Test (Windows Vista)" article explaining how to enable the test modes.

There are two ways to successfully load VAC driver under 64-bit Vista and 2008 Server systems:

At early boot time, press F8 and select "Disable driver signature enforcement". In this mode, Windows will not check driver signatures during current session. But if you reboot Windows, you should press F8 and disable signature enforcement again. So you need to make selection at every boot.
Enable Windows test-signing mode by one-time issuing "bcdedit /set testsigning on" command from a command prompt (under Administrator account). This permanently allows Windows to load drivers signed by test certificates. After issuing bcdedit command, reboot Windows. 64-bit VAC driver module is signed by a test certificate named "Eugene Muzychenko (Test)" so it will be successfully loaded in the test-signing mode.

This KB article may reference additional files that are available on the FlexRadio Systems web site Downloads page. Please use the URL(s) below to download the referenced materials.

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Posted Thursday, March 19, 2009 by Administrator