B&K 4070A Manual Do Utilizador

 

 

BK Precision 4070A User Manual Rev.2.2 

37 

   NOTE: For wideband FSK (where the difference between Mark and Space frequencies is > 1.0 MHz), the output 
level may shift slightly between the mark and space frequencies.  The 4070A has internal leveling circuitry is 
disabled in this mo de, in order to offer higher FSK modulation rates.  

   NOTE: The level specified is a 50O loaded level. This is the level of the signal, which will appear across a 50O 
load connected to the SIG Out connector. Intoau open circuit, the output swing will be twice the value entered.  

   You can enter an offset voltage for the output signal. For more information on output offsets refer to section 4.4.  

 

   In Data Modulation mode this input functions as an external trigger input. Logic low-to-high transition on this 
input will trigger the transmission. This input has an internal pull down resistor so that the input is held at a logic 
low when this input is left unconnected. See section 2.0 for more information on the External Trigger Input. 

   To download the modulation data, you must send an ASCII message to the 4070A through the serial port.  To do 
this, first cable the PC’s serial port to the 4070A as shown in the Remote Operation section of this manual. 

 

   The following example has you generate an ASCII disk file and download it to the 4070A. If the file already has 
the “W M” header, you may use the WAVELOAD.EXE utility with the “no header” option (/N) to send the file to 
the 4070A. (See the chapter on Downloading Arbitrary Waveforms for more information on WAVELOAD.EXE). 
   You may also write your own program to send the data to the 4070A.  If you wish to use your own program, be 
sure to set the serial port parameters to1 start bit, 8 data bits, 1 stop bit, and no parity. The baud rate of your program 
must also match that of the 4070A. To inspect or change the 4070A baud rate, press the Mode key and then the 
Offset key. 
   Modulation Data is sent to the 4070A in Hexadecimal format.  (For more information on hexadecimal numbers, 
refer to the chapter on Hexadecimal Format in this manual).  The message consists of a two character header. Bit 
count word, and the modulation data words. It does not matter what mode the 4070A is in when the data is 
downloaded, however you must switch to Internal FSK mode in order to transmit the message. 

   The message is best explained by example. An example message is: 

W M 0012 FE96 AA20 X 

It breaks down as follows: 

W  

- This is the first character. It tells the 4070A to download data from the user

 

M  

- This character tells the 4070A that the data is MODULATION data (as opposed to an arbitrary 

 

 

   wave form)

 

0012  

- This is the bit count. In this case, the message is 18 bits long (0012 in Hexadecimal is 18 in base 10) 

                 960 bits maximum.

 

FE96 

- This is the first 16 bits (one word) of the binary message. The first bit to be transmitted is the MSB  

                 of  this word. 

 

AA20 

- This is the second 16 bits of the binary message. Since the message is only 18 bits long, only the MSB 

                and the next lower bit will be sent (in this case a 1 then a 0). After the last bit is sent, the 4070A turns off 
                the carrier and awaits another trigger condition. 
X 

- This character denotes the end of the data and is optional. If the “X” character is missing, the 4070A will 

                 assume all data has been sent after 1-second time-out. 

 

The 18-bit message for the data

 FE96 AA20 is 

sent as follows:

 

 

1111     1110     1001     0110     10 

 

First bit transmitted   

        

 

Last bit transmitted 

 

Since this message is only 18 bits long, the last 14 bits of AA20 are ignored.