I have noticed that the Verdex pro seems to put out a whole lot of radio frequency interference.  So much so that it blocks reception of GPS signals as well as a handhelp GMRS radio I wired into it.  It's sitting on my desk next to a wireless mouse and seems to cause problems with that as well. 
You might try putting the verdex behind an RF shield and see what happens.  I have not tested it with a spectrum analyzer but based on anecdotal evidence I'm guessing its quite noisy. 

From: Connie C <cciarleg@umd.edu>
To: gumstix-users@lists.sourceforge.net
Sent: Sunday, April 19, 2009 2:29:49 PM
Subject: [Gumstix-users] Serial Receive Issue


Hi,

I have an AerocommAC4790 radio on the FFUART on a Verdex-pro xm4.  I can
successfully send data packets to a separate computer with a radio hooked
up.  I'm not receiving anything however.  I've got a read set up that should
have a reaction to anything being received by the radio.  I know the port
and the radio both work.  I would appreciate any pointers as to where I'm
going wrong reading the port.  The basic code looks like:
To read the port:
pread(char *buf, int length)
{
    curr_char=buf;
    bytecount=0;

    if( (bytecount=read(fd, curr_char, 1)>0) && (length+buf)>curr_char )
        buf+=bytecount;

    return curr_char-buf;

and I've tried 2 functions to grab packets from the radio:
receive_data(char* buff)
{
    for(int i=0;i<BUFF_SIZE;i++)
    {
        int temp=myport->pread(&buffer[i], BUFF_SIZE-i);
        buff[i]=buffer[i];
    }
    return 0;
}
and
get_packet(char*  buff, int length)
{
    //First, read more data
    buff_index+=myport->pread(&buffer[buff_index],BUFF_SIZE-buff_index);
    //Have we reached the packet end?
    temp=0;
    for(int k=0; k<buff_index-CHECKSUM_SIZE; k++)
        if(buffer[k]==PACKET_END_CHAR)
        {
            temp=k+CHECKSUM_SIZE+1; //The full size of the packet
            k=buff_index; //exit loop
            if(temp>length)
                return -1; //buffer is smaller than packet size
            for(int j=0; j<temp;j++)
            {
                buff[j]=buffer[j];
            }
            //Copy data that isn't part of this  packet to the beginning of
the array
            for(int j=temp; j<buff_index; j++)
            {
                buffer[j-temp]=buffer[j];
            }
            buff_index=buff_index-temp;
        }

        return temp;
}

Neither of which have any reaction to incoming packets.  The main program
operates in a loop and continuously checks for packets.  Is this an
incorrect read of the port?
Thanks. 
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