[RFI] wireless power transfer via 160M band

[Hare, Ed W1RFI]

Most of the systems I know of are adjusting the transmit frequency for maximum power transfer.  This is somewhat dynamic, so the fundamental signal of these devices tends to wander a few kHz, making the higher-order harmonics wander quite a bit.  

If these devices are inductively coupled, as most of the ones I know of are, then the fields diminish rapidly with distance.  A device that charges as a distance has to, well... radiate a signal at a distance, and we can't expect a 1/r^3 decay in field strength from a radiating sytem.  

Higher powered chargers could operate under Part 18 and have power in an ISM band be unlimited. However, there is no ISM band in the MF and LF bands where most of the chargers operate nowadays.  The low-powered ones operate under Part 15, and have relatively low emissions, but higher-powered ones in the MF and LF bands will probably need a waiver to be able to do things like charge electric vehicles.   If given, this waiver would probably be only for the fundamental frequency, with harmonics and other spurii still meeting Part 15.

I will ask around. I am a member of a ANSI C63 committee working group that is developing standards on how these devices should be tested.

Ed, W1RFI


-----Original Message-----
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Dennis Monticelli
Sent: Wednesday, February 07, 2018 12:30 PM
To: rfi at contesting.com
Subject: [RFI] wireless power transfer via 160M band

This has been researched in the universities.  MIT made some PR on it several years back.  My former employer was close to this research activity.  The idea is for the receiver to be in the near (induction) field of the transmitter and tuned to the exact frequency.  But in order to get a decent throw distance some serious power is required and the efficiency of capture is low.  Where does the wasted power you ask?  It does into heat, it goes into nearby wiring, it gets radiated for hams to pick up.  BTW, most wireless charging does take place after dark when people return home and/or are sleeping.

I suggest that the ARRL take the lead in determing the noise signature of this particular experiment and make that info available to the amateur community so we will know when we receive it. Without reports of intercepted interference the FCC will not act.

Generally it is just a carrier with some low bit rate modulation that feeds back sync info to the transmitter.  If the receiver and transmitter do not have their hi Q circuits locked the power transfer efficiency is very low.
There are schemes that adjust the TX and there are schemes that adjust the RX or RX's.  The wavelength must be long enough for a receiver to be in the induction field regardless of where it resides within the home but not so long that it is impractical to have efficient tuned loops, hence the desire for 160M.

BTW, I have no knowledge of the scheme that this Texas company is using.
It may be different.

Dennis AE6C
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