SpinCore Technologies RadioProcessor USB User manual

RadioProcessor™ USB
Low Frequency Operation Manual
SpinCore Technologies Inc.
http://www.spincore.com

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SpinCore Technologies Inc.
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© 2010 SpinCore Technologies, Inc. All rights reserved.
SpinCore Technologies, Inc. reserves the right to make changes to the product(s or information herein without notice. RadioProcessor™,
PulseBlaster™, SpinCore, and the SpinCore Technologies, Inc. logos are trademarks of SpinCore Technologies, Inc. All other trademarks
are the property of their respective owners.
SpinCore Technologies, Inc. makes every effort to verify the correct operation of the equipment. This equipment version is not intended for
use in a system in which the failure of a SpinCore device will threaten the safety of equipment or person(s .
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Table of Contents
I.Preparing the Board for DC Operation...............................................................4
II. Operating at Low Frequencies.........................................................................5
Acquisition Parameters.....................................................................................5
III.Receiver Characteristics..................................................................................6
Acceptable Input Voltage Range......................................................................6
Frequency Characteristics................................................................................6
IV.Contact Information..........................................................................................8
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I. Preparing the Board for DC Operation
The receiver of the RadioProcessor is capacitively coupled, leading to attenuation at
low frequencies. To operate at low frequencies, it is necessary to remove the capacitor (C680
at the input of the RadioProcessor. Illustration 1 below shows the location of C680.
NOTE: Removing the capacitor at C680 will introduce a DC offset in measured values when
the receiver is loaded. See the section below on handling the DC offset.
To prepare the board for DC operation, please follow the following steps:
1. Carefully remove capacitor C680 from the receiver of the RadioProcessor (see
Illustration 1 above for the location of C680.
2. Connect the pads at C680 using either a small piece of wire or solder.
3. Verify continuity between R603 and connection created in step 2.
4. Verify that there is no short between C680 and C605.
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Illustration 1: Location of C680

II. Operating at Low Frequencies
Acquisition Parameters
The filter pipeline of the RadioProcessor contains a CIC filter with a cut-off frequency of
approximately 1 kHz. At low frequencies when using base-band conversion, the result of the
conversion leads to spurious peaks in the pass-band of the CIC filter. To avoid these spurious
peaks, it is necessary to set the spectrometer frequency to 0 Hz.
DC Offset
By removing the capacitor at C680, a DC offset will be introduced into the receiver.
This offset can be eliminated in software by first calculating the DC offset at the receiver when
loaded by a 50 Ohm capacitor, and adjusting the values of data acquired. To remove the DC
offset:
1. Terminate the RadioProcessor receiver using a 50-Ohms terminator.
2. Acquire data using at least 1024 points and a spectrometer frequency of 100
Hz.
3. In software, calculate the average value of the data captured by the
RadioProcessor.
4. Modify the acquisition program to apply offset correction by subtracting the
value calculated in step 3 from each point of data downloaded from the board
before storing it to the FID.
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III. Receiver Characteristics
Acceptable Input Voltage Range
Testing of the RadioProcessor with C680 removed showed that the receiver is linear
within the tested range of 0.5V to 2.0V.
The input voltage to the RadioProcessor must be positive. To measure a range of
voltages from negative to positive, introducing a DC offset that will shift the required voltage
range into the linear operating region of the RadioProcessor is acceptable.
Frequency Characteristics
Illustration 2 below demonstrates the characteristics of the RadioProcessor at low
frequencies. The green line represents the characteristics with capacitor C680 and the CIC
filter enabled. The capacitor leads to a large attenuation at low frequencies, while the CIC
filter attenuates higher frequencies.
The red line represents the characteristics of the receiver once the capacitor C680 has
been removed from the receiver circuit. Once the capacitor has been removed, low
frequencies down to DC can be acquired by the RadioProcessor. The CIC filter was enabled
for this test, leading to attenuation at higher frequencies.
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Illustration 2: Low frequency characteristics of the RadioProcessor receiver.
Capacitor Removed
With Capacitor

The data shown in Illustration 2 was collected by performing scans and taking the
maximum magnitude point acquired for each frequency. The spectrometer frequency was set
to 0.0 Hz, and the spectral width was set to 2 kHz for each acquisition.
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IV. Contact Information
SpinCore Technologies Inc.
Telephone: [phone]
Web Form: http://www.spincore.com
Product URL: http://www.spincore.com/products/RadioProcessor/
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