EECE 380 – Design Studio III
Technical Memo 1
Project Team: L1—B4
Names and Student Numbers:
Omar Omari
Michael Long Li
Qian Fang
Nat Wongpatimachai
54434105
28084101
55983100
54589106
Team Organization Meeting – Outcomes
Tuesday 17th September, 2013:
We went through the Group Activity checklist provided by Dr. Michelson. We discussed our
strengths, weaknesses and interests so that we can all be aware of what skills we are most
confident about, and what skills we would like to develop. We elected Omar Omari to be the
group leader for this week and next week. We all agreed to meet on Tuesday, Thursday, and
Friday at 5pm every week.
We created a blog for our group where we will post our memos, important group updates and
shared files.
We asked questions about the Spectrum Analyzer’s and Magnetometer’s purpose and use in the
project. We also asked questions about the schematic diagram from the previous lecture.
We researched the term ‘DC interference’ and its relation to the MRI and NMR. We found that
MRI and NMR are sensitive to small changes in DC fields; so we need to build the
Magnetometer to measure the intensity of magnetic fields created by changes in the DC field,
which will cause interference with the MRI and NMR imaging systems. Through this, we
understood why the MRI and NMR instruments need to be placed in a stable DC field with low
DC interference.
Through group discussions with the help of the T.A., we have a more clear understanding of the
project’s final outcome. For the Magnetometer, we need to measure the magnetic field intensity
created by the DC interference, and for the Spectrum Analyzer, we need to measure AC
interference.
We were given assignments to review specific circuit components for the Spectrum Analyzer,
and explain to the group the purpose of these components. Our group leader Omar was assigned
to investigate the schematic diagram for the Spectrum Analyzer and explain how the device
works in our next meeting, which is on Thursday 19th of September.
Thursday 19th September, 2013:
We discussed each of the components in the Spectrum Analyzer schematic diagram to get a
better understanding of how the Spectrum Analyzer works.
To gain further understanding of the filters in the schematic diagram, Omar and Nat were
assigned to investigate the filters to find out their purpose and, if possible, their specifications.
Qian was assigned to further investigate the SA602A Mixer to find out why we are taking the
difference of the RF and Local Oscillator signals, and any other useful information. Michael was
assigned to research on how to build the Magnetometer.
We were all asked to compile a list of questions to ask the TA and the professor if we were
unsure about anything that we find during each of our investigations.
Sunday 22nd September, 2013:
By researching the magnetometer, Michael found out that a current flow in an inductor will
create magnetic field around it. By changing magnetic field through a looped inductor, it can
generate current flow through the inductor and create a voltage difference. By amplifying the
voltage signal and checking it with an oscilloscope we can find the magnetic field change in the
inductor. Furthermore, by supplying an alternating current to the inductor and setting the
resulting stable magnetic field as a reference, any magnetic interference around the inductor will
create a voltage difference. Using the voltage difference, we can measure the difference between
the external magnetic field and the reference magnetic field to obtain the magnetic field
interference.
From the investigation, Nat found the correlation between some of the filters used in the
schematic and the recommended ratio or specification for them in order for the Spectrum
Analyzer to function at an optimum performance. Nat also found several equations that can be
useful later on during the circuit design and the debugging part of the project.
By looking into RF amplifiers and reviewing the SA602A Mixer datasheet, Omar derived a
relationship between the maximum input frequency for the Mixer and the 3dB frequency for the
“Preselector-Low-Pass filter”. This relationship can be used to determine how much the Input RF
signal should be attenuated by the RF Attenuator, and thus provide the necessary specifications
for a particular RF attenuator component.
From the SA602A datasheet the maximum RF input frequency to the Mixer is 500MHz.
However, the Mixer is designed for optimum low power performance; therefore we cannot just
simply input 500MHz. The datasheet specified that at 45MHz, the amount of noise produced is
less than 4.7dB, so the RF input signal must be attenuated to a range of 45MHz +/- 10MHz for
example, in order to reduce the amount of noise input from the RF input signal. Therefore
assuming the worst case scenario using the above example, the 3dB frequency of the PreselectorLow-Pass filter would be approximately 55MHz. Therefore, we now know that we need an
Operational amplifier that has a 3dB frequency of around 55MHz to design our Preselector-LowPass filter.
From the research Qian did, she found out that the purpose of the mixer in the spectrum analyzer
is that it shifts signals from one frequency range (of the input signal to be processed in this case)
to another frequency range of the receiver. In this way, frequency of the receiver does not need
to be changed as long as we input signals of different frequencies from the local oscillator input
channel controlled by myDAQ. Since the mixer produces new signals at the sum f1+
f2 and difference f1-f2 of the original frequencies, Qian assumed that it depends on whichever
frequency is within the frequency range of the receiver that can be used as input to the receiver.
But this point needs further confirmation.