5600 lowest frequency

[madd]

Hello

According to NI 5600 downconverts any frequency to 15Mhz(with 20Mhz bandwidth). but specification says 5600  has a range of 9Khz -2.7Ghz. what if the input frequency is 9Khz or lower than 15Mhz. what does it do .does it upconvert the signal to make 15Mhz  or what? i have seen a badpass filter in the block diagram of 5600 (not a low pass which always downconverts the signal ) in inital stage of 5600 does this bandpass act as highpass for lower frequencies than 15Mhz . am i right or no

Regards

Madd

[Speedy_Badger]

Hi Madd,

You're initial thought is correct. Frequencies below the 15 MHz IF output are upconverted. More interestingly however is that the first mixer stage of the PXI-5600, see the block diagram in the NI RF Signal Analyzer Help or NI-5660 Help, always upconverts the signal.

Let's break down the signal chain portion of the block diagram:

• 1: The Low Pass filter here ensures that the signal we are manipulating has significant power confined to within the 2.7 GHz range of the device.
• 2 & 3: This first mixer upconverts the signal to an IF frequency, allowing us to spread out the images and harmonics that result. We can then filter this signal to focus in on the pertinent information as well as ensure qualities such as passband flatness.
• 4. We then downconvert the result from the BPF in step three to another IF frequency.
• 5. This BPF is the actual filter which sets the 20 MHz bandwidth of the 5600 device. It also allows us to do further conditioning of the signal.
• 6. The result of step 5 is then downcoverted with this mixer to the IF frequency you mentioned, 15 MHz +/- 10 MHz.
• 7. A final LPF is used to condition the IF output signal before it is sent on to a digitizer or third party device.

Hopefully this gives you a better impression and understanding of the signal chain.

Best Regards,

Message Edited by Speedy Badger on 07-08-2008 08:47 AM