1import visa
import time

###  Agilent N9340B spectrum analyzer
instrument_descriptor = 'USB0::0x0957::0xFFEF::CN03490905::INSTR'
AFG = visa.instrument(instrument_descriptor)

###  I/O timeout for exception raising
AFG.timeout = 100

print AFG.ask('*IDN?')

###  Reset and clear the AFG status
AFG.write('*rst')
AFG.write('*cls')

###  Set the analyzer center frequency (Hz)
AFG.write('SENS:FREQ:CENT 1e6')

###  Set SPAN
AFG.write('SENS:FREQ:SPAN 2e6')

###  Start Freq
AFG.write('SENS:FREQ:START 750kHz')

###  Stop Freq
AFG.write('SENS:FREQ:STOP 970kHz')

###  RBW
AFG.write('SENS:BAND:RES:AUTO 0')
AFG.write('SENS:BAND:RES 1kHz')

###  VBW
AFG.write('SENS:BAND:VID:AUTO 0')
AFG.write('SENS:BAND:VID 300Hz')

###  AMPTD
AFG.write('SENS:POW:ATT:AUTO 0')
AFG.write('SENS:POW:ATT 0dB')

###  Ref Level
AFG.write('DISPlay:WINDow:TRACe:Y:RLEVel -30dBm')

###  Set screen Scale
AFG.write('DISPlay:WINDow:TRACe:Y:PDIV 10')

###  Set averaging 
AFG.write('SENSe:AVERage:TRACe1:COUNt 2')

###  Turn on averaging
AFG.write('SENSe:AVERage:TRACe1:STATe 1')

###  Measure loop
i = 0
while True:
	###  Continuous <1> or Single Sweep <0>
	###  AFG.write('INIT:CONT 0')

    ###  Run measurement immediately
	AFG.write('INIT:IMM')

	###   This command causes the instrument to wait until 
	###   all pending commands are completed before 
	###   executing any additional commands
	AFG.write('*WAI')

	###   6 peaks search
	AFG.write('CALCulate:MARKer:ALL')

	###   Query and read the marker1 frequency [Hz] 
	print AFG.ask('CALC:MARK1:X?')

	###   Query and read the marker1 amplitude [dBm] 
	print AFG.ask('CALC:MARK1:Y?')

	###   Restart averaging
	AFG.write('SENSe:AVERage:TRACe1:CLEar')

        ###  Number of  loop execution times
	i = i + 1
	if ( i > 3):
		break