Induction Loop "Antenna" in Attic for 60Khz (WWVB) - Page 1
Forum section: electronics / rf-microwave

author: pelud
author_rank: Regular Contributor
timestamp: October 29, 2021, 11:10:09 pm
content: I live in an area that doesn't receive WWVB time signals, and I would like to create some sort of mini transmitter for it for my house. I have created a small ESP8266/ESP32 sketch that works well with a battery powered radio controlled clock movement and a few coils of wire.I've read that building-wide induction loops are a common thing in Churches for heading aids; is it feasible to make something for 60Khz? I was hoping something like this wouldn't radiate much but could still be picked by the the little loopstick antenna in the clock movement.I also thought I saw something about this in a magazine a long time ago, but I can't remember where nor the details.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 30, 2021, 03:31:58 am
content: Make a loop of 22 AWG or so wire around the room near the ceiling (ideally near the center of the house, bigger room is better), then measure the inductance and add a capacitor to resonate at 60kHz. Most likely it would be easiest to have it series resonant since the capacitor will also block the DC bias of the PWM output. Then add series resistance as needed to stay within the current rating of the logic pin.

author: radiolistener
author_rank: Super Contributor
timestamp: October 30, 2021, 08:36:26 am
content: Quote from: pelud on October 29, 2021, 11:10:09 pmcan you please explain what did you mean?

author: pelud
author_rank: Regular Contributor
timestamp: October 31, 2021, 07:03:56 pm
content: ok, as an experiment I will try putting a loop of wire around the outside of the house and see how it works.I was worried that perhaps I would be creating interference, but I assume that the wavelength is just too large to actually propagate.

author: pelud
author_rank: Regular Contributor
timestamp: October 31, 2021, 07:05:45 pm
content: They are called "hearing loops" or "audio induction loops". They create a magnetic field within the room or building that can be picked up by a dedicated receiver.Here is a website that explains it in more detail:https://www.hearinglink.org/living/loops-equipment/hearing-loops/what-is-a-hearing-loop/

author: tkamiya
author_rank: Super Contributor
timestamp: November 01, 2021, 02:05:46 am
content: I think that DIY WWVB misses all the point of having WWVB in the first place. Whatever you do will be less certain than your best standard frequency/time base. I understand if you'd want to experiment; however.... If I were to do this, I'd put a big loop in the attic and forget tuning it to 60KHz. If you are inside (or directly below) your transmission antenna, even very low power should produce a favorable result.As to hearing loop, I recall Disney used to do this for speakers of languages other than English. (mainly Spanish). While mass will hear in English directly, ones with receiver you rent will get you the language of your choice.

author: pelud
author_rank: Regular Contributor
timestamp: November 01, 2021, 04:52:35 am
content: Quote from: tkamiya on November 01, 2021, 02:05:46 amI just want to have the battery powered analog wall clocks show the correct time; this seems like the easiest way to do it. I'm not that concerned with sub-second accuracy.

author: pelud
author_rank: Regular Contributor
timestamp: November 04, 2021, 04:29:56 pm
content: I decided to just try putting a wire around the perimeter of a single room at one end of my house. I used some old telephone twisted pair that I connected in parallel.The "loop" measured approximately 22uH with the single square loop formed around the room (approx. 10'x15'). I played around with the signal generator, and I found that about 320uF of capacitance is about right to make it resonate near 60kHz.I connected the output from the ESP32 to the loop with a 330 ohm resistor to limit the current and help filter out the square wave. There is a nice sign wave on the loop of about 0.5 to 1V P-P.If I connect a 60kHz ferrite antenna directly to the input of my scope, I can receive about 15mV P-P of signal depending on where I wave it around within the room.I can put a clock on the on the other side of the house and it has no problem receiving the signal.