Output relating to my work on coupled-coil wireless-power transfer by magnetic resonance.
My work over the past fifteen years has revolved around this kind of output
Where a pair of 30mm-radius, three-turn, inductive loop coils illustrate that 5V DC power can be thusly utilized to power wirelessly.
TODO: Calibrate the graticules and rephotograph for ease of viewing. Discuss and document the calibration in the appropriate repos.
There is a task to measure the coupling-coefficient between two 12mm radius, ten-turn, inductive loop coils. It is interesting to know whether the efficiency is better or worse with small coils verses the larger ones that can power lamps at a distance. We would like to determine emperically what are the losses across a frequency sample (band); in this case, between 100 kHz and 100 MHz.
Using the hp8601A Sweeper/Generator in tracking generator mode, one can observe the linearity of two 12.5mm-radius, 10-turn inductive-loop coils on a hp141S Spectrum Analyzer. Before we can do this, the hp8601A is set to run as a tracking generator by modifying the internals in such a way as to direct the VTO out and the 1st LO in.
Where the input for the 1st LO will come as an output from the hp8553L RF Section plug-in for the hp141S Spectrum Analyzer. As the hp8601A OPT007 that has this particular feature is nearly impossible to find, I made the appropriate modifications according to the Service Manual. To note, the schematic shows a RF amplifier but I opted to test if the modification would work without as the amplifier is a passive type meaning it would only engage if following too low a power value required by the VTO board. I did have an hp8447A at-the-ready should amplification be required (drift from the set power) if it were to not be included. I tend to do this with Hewlett-Packard test equipment as, from experience, they are over-built rather than under-built. Draft testing showed the amplifier not required at the 8601A-007 input and there is enough signal strength to traverse a 3m cable between the hp8601A and the hp141S/8552A/8553L set perpendicular to one another.
When using in a single-frequency setting, one can turn the knob on the hp8601A to change the output;
for the purposes of this experiment the entire range will be applied to the coils that are attached by a special cable to the BNC cables to each piece of test equipment.
When powered-on, the following is displayed on the hp141S.
Where one can see how the coupled-coil arrangement performs under the frequency range of interest.
Observing that the output power of the hp8601A is set to -30 dbm and the meter-trim set to 0 -- from the figure it reads -2 meaning it actually has an output value of -32 dbm -- this is the sweep power for every frequency sent across the band and is visible on the display. In order for the calibration between the two pieces of test equipment, they should be set in a referential manner -- meaning the LOG REF setting on the hp8552A IF Section plug-in is also set to -30 dbm. Therefore, one can determine the linearity of the coupled-coils over the entire sweep.
100,000 - 100,000,000 | 50 graticules - TODO: Write a mathematical expression
On the spectum analyzer display screen, the dashed-line bisecting horizontally is the -30 dbm reference line, as it shares this with its internal calibration signal. The graticule indicators along the bottom are from low (the left) to high (the right) as this is in tracking generator mode rather than center frequency mode. What is the graticule to measure the result is the one traversing the center of the screen from LIN to LOG. By examination, one can see that the coil arrangement has a peak coupling (minimal loss) at the fourth graticule 2 MHz then which slowly increases losses reaching is maximum value at the thirty-fifth graticule 75 MHz at -43 dbm, then rises in efficiency to -40 dbm level at the end of the sweep. We could state that it would be most efficient to have the circuit perform at the 2 MHz frequency indication.