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  1. logbook

    Q-factor of spring on a Rotary Actuator

    I have just designed and built a rotary actuator which uses flexures rather than bearings. These things are essentially springs which have the ability to support an armature and allow several degrees of rotary action against a light spring force. I have just done an open loop test on the device...
  2. logbook

    ANSOFT Designer: Non linear AM simulation

    Can anyone tell me how to set up the basics of a non-linear AM simulation in Designer. The help files are non-existent and our ANSOFT support expired. Basically I reduced the circuit down to almost nothing, a source with AM on it and a resistive load. I did a 1-tone harmonic balance simulation...
  3. logbook

    PICDEM2+ LCD problem

    I just bought this PICDEM2+ demo board. £56 from RS components. Wonderful little thing with all sorts of goodies. Run up the pre-programmed demo code and it does lots of good things. Then comes the hard bit. The demo code is in assembler, and lots of it. Hundred of lines of code per file. Of...
  4. logbook

    Directivity of a Directional Coupler

    I guess this is a similar question/problem to my last question on waveguide spacers. (These are factual statements not academic thought experiments) I have a 10dB directional coupler with a claimed directivity of 30dB. I have four nominally identical terminations each claiming to have a VSWR of...
  5. logbook

    Waveguide offset pieces (spacers) for calibration

    I thought I had understood waveguide offsets (an empty waveguide spacer section) to estimate mismatch errors, but it seems I was over-confident. I bought a quarter wave offset waveguide section to reverse the mismatch error in my scalar measurement system and therefore give me an uncertainty...
  6. logbook

    Waveguide "cookbook"

    Has anyone seen a sort of waveguide cookbook for the tuning structures that you need to put into T-junctions and magic-Ts to make them work at all? It is evident from my HFSS simulations that untuned structures are no use at all at all frequencies in the pass-band. I am of course running...
  7. logbook

    Cavity Modes

    I have been searching my microwave textbooks for information on rectilinear cavity modes and have found very little practical information. For standard rectangular waveguide we have simple rules like the height is half the width making the next pair of modes 2:1 above the dominant mode. A cubic...
  8. logbook

    What happened to Agilent components?

    Did I blink and miss something? I was looking for the Agilent/HP range of pHEMTs and microwave detector diodes and I couldn’t find any components on the Agilent web site. Has this section been sold off or something. I looked at the history page on the Agilent website and the number of employees...
  9. logbook

    Convection Time-Constant in Air

    My book on heat flow analysis does not help me with respect to the time-constants involved with natural or forced convection in air. My application is just an ordinary electronic circuit bolted to an ordinary finned aluminium heatsink. I could calculate the steady state temperature rise from...
  10. logbook

    "Force" Window function

    I have been asked to help code the "Force" window function in a C++ application. I did the original window functions rectangular, Hamming, Hann, flat-topped, and so forth, so I have the original papers by Harris, Nuttal etc, but I had never heard of the Force window until asked. I have googled...
  11. logbook

    Waveguide open-circuit?

    I am trying to work out how to calibrate a return loss measurement jig in waveguide. The system is just a CW power source, two directional couplers and two power meters. I thought that I could put on a short-circuit piece and an open circuit piece and say that both should give 0dB return loss...
  12. logbook

    DAC7571 latch up

    I am running a DAC7571 12 bit I2C DAC from a 5V rail butteh load is going to a -5V power rail, the Thevenin equivalent circuit being a 1240R resistor to -3.8V. At power up the DAC latches at -2V and will not recover. This circuit and this load worked fine on the last two issues of pcb and now it...
  13. logbook

    OpampÆs Aberrant Input Offset

    I designed in a TLC082AID dual opamp into my brand new circuit. First batch worked fine. Second batch were a pile of pooh. Checked the opamps themselves and the input offsets were over a mV in some cases. The data sheet claimed 0.75mV worst case at room temperature. So I have had to make a test...
  14. logbook

    Resonances in a scanning mechanism

    I am trying to understand the resonances in a scanning mechanism being developed where I work. The mechanism is driven by a stepper motor via an offset bearing and pushrod to give a reciprocating motion of a few degrees. The stepper motors are only of the order of 2 watts, so we are not talking...
  15. logbook

    Inertial Load Referral to a DC Motor Shaft

    This is not a student posting even though it may sound like a homework question. I am phrasing the question in a fairly general manner because the project is very sensitive. I have a DC motor driving what is essentially a purely inertial load. The load is minimal except when being accelerated...
  16. logbook

    Detector Noise

    I am trying to work out how to investigate the noise in a diode based detector circuit theoretically (that is, before I build it). For the sake of the discussion let’s consider a 10MHz carrier with 0.1% 1kHz AM. I want to run the detector diode at a relatively low power level so it is used in...
  17. logbook

    Galvanically Isolated Waveguide?

    Is anyone aware of galvanically isolated waveguide sections? I was thinking about earth loops in the DC end of the system and how to prevent them, and it occurred to me that the field would jump a small gap in the waveguide, so it should be relatively straight forward to put an insulating shim...
  18. logbook

    CPW SM attenuator chip

    I am using a nice little 3dB surface mount attenuator, roughly 0805 size, which works up to 20GHz. Unfortunately it only has three terminals; in, out, and ground. What I really want is the same thing but with two ground terminals so it fits more symmetrically on coplanar waveguide. Has anyone...
  19. logbook

    Extending the range of wireless networked pc

    I have a Belkin FSD7010 802.11g wireless notebook network card and I want to extend the range. Unfortunately there is no external antenna socket on it to allow me to connect up a yagi antenna or a cantenna to boost the signal. However it seems to me that I ought to be able to reactively couple...
  20. logbook

    Transmission/Reflection Frequency Response of a Polarising Grid

    I have been trying to find out some quantitative information on polarising grids for RF/microwave signals and despite checking over a dozen electromagnetics and physics text books I have found almost nothing. In the early experiments of Hertz 66cm waves were passed through a polarising grid...

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