Anything important operate on ~980Khz? - Page 1
Forum section: electronics / general

author: Things
author_rank: Regular Contributor
timestamp: March 27, 2013, 03:20:59 pm
content: Just curious, I've built a plasma speaker Tesla coil that operates around 940-980Khz at around 100W, wondering if anything important works within these ranges, so whether I can expect random vans to start appearing out the front of my houseDan

author: Balaur
author_rank: Unknown
timestamp: March 27, 2013, 03:27:59 pm
content: Quote from: Things on March 27, 2013, 03:20:59 pmHeh, heh. That frequency is smack in the middle of the AM medium wave band. Just tune your radio to it and find what you can hear.

author: c4757p
author_rank: Super Contributor
timestamp: March 27, 2013, 03:28:17 pm
content: AM radio. I doubt that's the only frequency you are broadcasting on, though. I don't have much experience with Tesla coils but I suspect they are decent wideband jammers.

author: Things
author_rank: Regular Contributor
timestamp: March 27, 2013, 03:55:40 pm
content: Haha no kidding, grabbed an AM radio and I can actually hear the audio it's playing too! Only reaches to about my driveway, but not bad considering it wasn't designed to be a radio transmitter (At least, most tesla coils these days aren't, I know that was kind of Tesla's intended purpose).And you're correct about it being a jammer, almost instantly wipes out my modem, and it almost killed my camera's SD card! Also wipes out the station on the AM radio as soon as I turn it on.Interesting stuff

author: c4757p
author_rank: Super Contributor
timestamp: March 27, 2013, 03:58:08 pm
content: Quote from: Things on March 27, 2013, 03:55:40 pmThat's good. Like I said, I know jack shit about Tesla coils, but I'd expect the fundamental to be the strongest output frequency. If the fundamental is only reaching your driveway at least you're not jamming up the whole neighborhood.

author: c4757p
author_rank: Super Contributor
timestamp: March 27, 2013, 04:01:15 pm
content: At least 2.4 GHz isn't a harmonic. You know your fun will be ending very soon if you start messing with people's Wi-Fi.

author: kc0ngu
author_rank: Contributor
timestamp: March 27, 2013, 04:11:49 pm
content: You built a spark transmitter - sort of, so expect your generating all sorts of harmonics, thats why the radio pioneers soon looked to develop better ways of getting there signals out. Depending on how much power you are actually generating at whatever is acting as an antenna in your set up will determine how much activity you are creating havoc with.Have fun, but be aware you are likely to become noticed if you continue long enough.

author: Things
author_rank: Regular Contributor
timestamp: March 27, 2013, 04:49:27 pm
content: Well, the thing draws about 96W total, so take say 300mA of that for the control electronics, say 1A in heating/losses roughly, I'm probably looking at about 50W of transmitting power. Although a fair bit of that would be lost in the arc as heat too etc. Still, waaaayyyyyy more than whatever the legal limit is.Who listens to AM anymore anyway?

author: c4757p
author_rank: Super Contributor
timestamp: March 27, 2013, 05:03:02 pm
content: Quote from: Things on March 27, 2013, 04:49:27 pmWell, I'd guess that the vast majority of that 96W is the arc itself!

author: AlphZeta
author_rank: Regular Contributor
timestamp: March 27, 2013, 05:58:36 pm
content: QuoteI am afraid your receiver wasn't sensitive enough. A QRP transceiver can communicate around the globe using as little as 3W RF power. The sparking produces a broad spectrum interference (like lighting) and the frequency you mentioned is the switching frequency of your circuit I assume so that itself generates some interference but the majority of the RF power would be generated from the spark.

author: ddavidebor
author_rank: Super Contributor
timestamp: March 27, 2013, 06:33:40 pm
content: Quote from: Things on March 27, 2013, 03:20:59 pmYou absolutely need a faraday cage surrounding the speaker

author: tom66
author_rank: Super Contributor
timestamp: March 27, 2013, 06:53:06 pm
content: You need to "cheat" -- add spread spectrum! Then you'll pass EMI tests and jam out more than 980kHz!

author: ivan747
author_rank: Super Contributor
timestamp: March 27, 2013, 08:56:32 pm
content: Quote from: Things on March 27, 2013, 04:49:27 pmDude! It is legal as long as there aren't cops around

author: Someone
author_rank: Super Contributor
timestamp: March 28, 2013, 01:00:43 am
content: Quote from: c4757p on March 27, 2013, 04:01:15 pmBut the first harmonic sits right in a navigation band, which is exactly the sort of thing that gets noticed by sensitive people. For the full Australian listing:www.acma.gov.au/webwr/radcomm/frequency_planning/spectrum_plan/arsp-wc.pdf

author: vk6zgo
author_rank: Super Contributor
timestamp: March 28, 2013, 03:33:39 am
content: Well,the upside is all the new friends you are going to make,from the irate neighbours,to the ACMA Inspectors,Police Officers,your Defence Lawyer,your Bank Manager when you try to get a loan to pay for your defence & huge fine,the Magistrate,& finally,when you get chucked in the hoosegow,your new special friend,Bubba!

author: Things
author_rank: Regular Contributor
timestamp: March 28, 2013, 05:40:16 am
content: Someone, looks like the link got shortened by the forum, it won't workIt's OK, the signal is flakey by the time it gets out of the house, combined with a tin roof, and in a valley, with a less than optimal antenna, it isn't gonna go far

author: codeboy2k
author_rank: Super Contributor
timestamp: March 28, 2013, 06:13:21 am
content: Quote from: vk6zgo on March 28, 2013, 03:33:39 amI hate Bubba the most

author: madshaman
author_rank: Frequent Contributor
timestamp: March 28, 2013, 07:02:37 am
content: Seriously though, fun and games aside. Imagine the fuzz showing up (guarantee they won't be technical people) and just taking everything in your house that's electronic and carting it away until someone who *is* technical has a time to sort out what's illegal and what isn't...Sure, it's unlikely that someone's going to get a warrant before anyone speaks to you first but do you want to take that risk?see:http://www.austlii.edu.au/au/legis/cth/consol_act/ca191482/s3f.html

author: c4757p
author_rank: Super Contributor
timestamp: March 28, 2013, 05:24:33 pm
content: Quote from: Someone on March 28, 2013, 01:00:43 amYeah, I figured there was a harmonic sitting on something important, I was just being a bit facetious.