The latest Saelig Newsletter focuses on Pico Technology news: their new 4444 4-channel differential scope and novel probes, new helpful tech videos, as well as useful tech tips. It's here: http://bit.ly/2mYhPPz
Rigol has published lots and lots of new app notes and videos to describe in detail the use of their products. 77 articles on scopes alone! 58 on spectrum analyzers, 39 on waveform generators. Quite a gold mine!
Clamp diodes are widely used in
analog electronic circuits. Like all real-world components, these diodes have
some non-ideal characteristics; this paper investigates some of these
characteristics for a few diode candidates. The AMETRIX® Instruments’ Model 101
Picoammeter is used for measuring these small currents.
Reverse biased leakage current
is a characteristic of concern for a clamp diode. Ideally the leakage would be
zero but this is the real world, so what can one live with? In a typical
application there might be two clamp diodes, one to +15 V the other to -15 V
and a common connection to the signal to be clamped. The leakage current drops
as the voltage drops, so if that signal is nearer to +10 V, then the lower clamp
diode would have more leakage than the upper one. So in such an application, a
diode with both low leakage and a fairly flat leakage vs. voltage would be
1 is plotted data of
leakage measurements versus reverse voltage. A quiet DC supply was used along
with an AMETRIX Instruments’ Model 101 Picoammeter to measure the current (and
yes, that is single-digit femptoamps you are seeing).
Comments about reverse leakage:
1.The SST4391 is rated for 35 V
gate-drain and gate-source
2.The SST4391 costs $0.057 each
3.The 2n3904 has a Vcb maximum of
4.The MMBT3904LT1G is $0.0231
5.The FLLD261 is $0.0275 each
6.The BAS16 costs $0.0151 each
7.The BAT54 costs $0.0204 each
8.The BAS70 costs $0.0323 each
9.The MMBD4148CC costs $0.0194
So even though there is a 3:1
price ratio between the most and least expensive, they are all < 6¢, so cost
is probably not a serious part of the decision process.
The forward voltage
drop is another diode characteristic to be considered for a voltage clamp.
These measurements were made as follows (the data is presented graphically in figure 2):
1.Forward bias the diode
with a quiet DC supply that has fine resolution; in this case an EDC calibrator
generator set to pulse, 1 Hz, 1% duty cycle, drive a mercury wetted reed relay.
Connect the relay contacts across DUT such that the DUT is shorted for 990 msec
and unshorted for 10 msec; this is to minimize self heating effects.
voltage with Tektronix MSO4104 scope with Model 100 Series' probes to
minimize the low forward current errors. Set the scope’s bandwidth limit to 20
MHz to minimize noise. Use the scope’s vertical channel’s offset mode and 10 mV
range, adjusting the offset knob until trace is in center of screen, then
document the offset voltage.
In conclusion, some
simple measurements can provide much insight into the components that you think
might be ideal in a given application; and they might reveal some things that
Low-cost Universal Serial Bus (USB) radio frequency (RF) signal generators have recently come on the scene in the wireless world. They promise to be game changers for many reasons. Until these devices came out, a prospective buyer had two choices when it came to RF signal generation solutions. The buyer could either purchase a $20K+ benchtop box with all the bells and whistles, or they could purchase a $6K narrowband “synthesizer”, either hard coded to one frequency, or with an RS-232 programming port to figure out. Both of these solutions would typically take eight weeks to deliver. They are generally build-to-order components.
USB RF signal generators are actually a hybrid approach to both of those options mentioned above—they can be much cheaper and deliver in a couple of days. A great (made in the USA) example is the Windfreak Technologies SynthHD Dual Channel Microwave Signal Generator for $1,279. This price is surprisingly cheaper than some RF test cables.
The device has two independent channels that can tune in 0.1 Hz increments from 54 MHz to 13.6 GHz. The SynthHD’s RF power is adjustable in .01 dB increments from -50 dBm to +22 dBm. It also has many modulation features including FM chirps. The relative phase between the two channels can be adjusted in .01 degree increments. It is a hybrid approach because the device can either be controlled with a PC graphical user interface (GUI) like benchtop test and measurement (T&M) equipment, or it can be programmed to function as a module inside a communication system without a PC, like the narrow band synthesizer mentioned above.
The SynthHD signal generator will generate sweeps. The sweeps can be single channel or dual channel. The device can sweep up or sweep down. It can also ramp up or down amplitude while sweeping. The sweep can be controlled with an external trigger to either perform a full sweep per trigger, or perform a single step. In dual channel mode you can program a constant frequency offset between the two channels for the sweep.
The SynthHD signal generator will generate hops. The GUI allows the user to program up to 100 arbitrary points with a frequency and amplitude in dBm. This table is stored onboard in nonvolatile memory. Like the sweep mode the user can then have an offset on the other RF channel, hop up the list, hop down the list, and work with the trigger input.
Additionally, the SynthHD signal generator will digitally modulate FM, AM, and pulse. FM can be a typical sinusoidal signal, or it can also be a chirp. AM can also be the t ypical sinusoid signal or it can be ramps. The modulations can be combined. Combining a pulse and a chirp allows the user to set up a frequency modulated continuous wave (FMCW) radar signal. You can even combine this with the sweep function. As an electronic warfare example, you could sweep a pulsed waveform across a range of frequencies. Rates can be very slow, or in the case of FM, up to 5 KHz. Of course, all of these features can be saved to the device; it will begin sweeping on power up without a PC connected!
Use the external Trigger connection to perform external modulation such as FM, AM and Pulse. More details here!!!!
Kenneth Wyatt - November 25, 2013:
Every once in a while, I discover a product that is so incredible I wonder why it hasn’t been
publicized more widely. This is the case with Windfreak Technologies $599 miniature RF generator,
the model “SynthNV” (Figure 1). In case you’re wondering, their company is named after the
Figure 1 - The Windfreak Technologies SynthNV RF generator weighs just a few ounces and easily
fits in your hand.
For months, I’ve been seeking a small RF generator that could replace the 40-pound monster I keep
under my workbench. What really caught my eye initially was that the generator could AM modulate
the RF output - perfect for radiated immunity pre-compliance testing! In addition, it will pulse
modulate the output - perfect for testing to the MIL-STD-461 and DO-160 standards. The RF output
level is sufficient to drive a near field probe with enough field strength to investigate susceptibilities
within a product’s internal circuitry.
But wait, there’s more! Here’s rundown of the features of this palm-sized jewel. Some of these
additional features will be reviewed in Part 2 of this series.
• RF sweep generator (34.4 MHz to 4.4 GHz at up to +19 dBm output)
• Network analyzer (34.4 MHz to 4.4 GHz)
• VSWR analyzer (using external power coupler)
• RF power meter (real time)
The generator is USB powered and can run on most Windows operating systems, including Windows
8. It also includes an external power adapter input, so it can be programmed into a given state and
then disconnected from the PC and run standalone as a local oscillator or RF generator. There is a
port that can source or receive an external 10 MHz clock, as well as an RF input port for measuring
power. This port is also used for the network analyzer function.
Figure 2 - The basic user interface for the generator is based on National Instruments Labview.
The well designed user interface (Figure 2) is based on National Instruments Labview and the
provided software includes the runtime engine for those who don’t own the full Labview software. It
installed and ran just fine on my Macbook Pro with Parallels 9 and Windows 8. There are several
tabs along the left half of the panel. These select the major functions of the instrument controller.
When in manual mode, the large knob tunes the frequency in preset steps of 1kHz, 10kHz, 100kHz,
1MHz, 10MHz and 100MHz. The user may also enter frequencies directly by typing in the data
blocks or by using a keyboard control in place of the large knob. The nominal +19 dBm RF output
power is controlled by the rightmost panel. There are two buttons controlling the preset output. The
High Power button will switch between the default high power or when pressed decreases the
overall power output by about 55 dB (Low Power). A second button turns the RF on/off. The slide
control further adjusts the output power by up to 31.5 dB. Note that the power scale is “dB’ and not
the actual output power in “dBm”. This can be confusing at first, because the natural inclination is to
assume the scale corresponds to the actual power output. This requires some mental calculations (or
confirmation measurement) to set the precise output level. I suspect one slick way to confirm the
desired power level is to run the output (through attenuators) to the “RFin” port to make that
measurement. One improvement might be to redesign the slider to conform to the actual output
power level - changing the scale according to the three preset power levels.
Effective non-contact torque
monitoring can help production
quality as well as identify machine
problems before they happen.
The importance of torque measurement
in manufacturing environments is a new
concept to some, but an everyday essential to
others. Realizing the enormous cost benefits
of measuring torque in rotating systems is
sometimes not recognized by those tasked
with improving profitability. The challenge is
to be able to monitor and measure torque as
accurately, unobtrusively, and economically
as possible. For continuous-manufacturing
processes where machines are driven by rotating
shafts, machinery failure and subsequent
downtime must be avoided in order to maintain
profitability as well as consistency of output. The
effective use of precision non-contact torque
monitoring instrumentation can preemptively
identify problems that might affect machinery
reliability—extremely important for situations
where a single machine failure can lead to costly