Trying to understand 1054Z with 200mV p2p noise/signal at 100MHz ? - Page 1
Forum section: electronics / beginners

author: julian1
author_rank: Frequent Contributor
timestamp: December 28, 2016, 01:00:03 am
content: Using a 9V battery as dummy DC source (source doesn't matter here )My 1054Z shows a clean 200mV peak to peak signal at 100MHz,It's AC coupled, timebase is 5ns. The factory probes are definitely set to 10x.The scope is 50MHz unhacked - so I'm somwhat surprised it even shows a clean signal.I've tried swapping probes, and swapping channel inputs with the same result. Input is hiZ (there's no physical 50ohm termination).Turning on the 20MHz BW filter and the signal drops to 70-80mV p2p.The only thing I can of is a couple of local FM radio transmitters in this area - 100.9 and 99.3. Would that make sense?

author: ataradov
author_rank: Super Contributor
timestamp: December 28, 2016, 01:11:20 am
content: What happens if you short the probe to ground? And what happens if you short the input BNC connector?

author: julian1
author_rank: Frequent Contributor
timestamp: December 28, 2016, 01:19:47 am
content: short the probe to ground and it's thereunplug the probe from the scope and it's gone.short the bnc on the scope with a short piece of wire (5cm) and me touching it and it's there.short the bnc with a bnc adapter and it's gone (edit actually can still trigger if increase vert-resolution one step) . but if i move my hand near (but not touching) it appears.

author: julian1
author_rank: Frequent Contributor
timestamp: December 28, 2016, 01:26:47 am
content: I've changed vertical resolution, but it's still there. And more pronounced when move hand near.

author: ataradov
author_rank: Super Contributor
timestamp: December 28, 2016, 01:28:24 am
content: Hm. Well, I guess it is possible that this is FM radio, and your body acts as an antenna.In absence of other ideas, I'd try to record a chunk of it and try to demodulate it to see what happens. You may want to hack the scope for bigger memory depth for this

author: DimitriP
author_rank: Super Contributor
timestamp: December 28, 2016, 02:03:16 am
content: A) Also get one of these and check your wall plugs ...https://images-na.ssl-images-amazon.com/images/I/71AGESwD7kL._AC_UL320_SR240,320_.jpgB) and last but not least use different wall outlets (in different rooms).C) unplug your TV and router and computer(s) and try again

author: BrianHG
author_rank: Super Contributor
timestamp: December 28, 2016, 07:39:25 am
content: Have you tried a FM radio next to the scope with the antenna really small or off. Are you getting a blank dead carrier, mute audio, at that frequency?

author: Simon
author_rank: Unknown
timestamp: December 28, 2016, 08:29:23 am
content: You will see whatever frequencies can be represented with 1GS/s, all the 50MHz does is attenuate it.

author: julian1
author_rank: Frequent Contributor
timestamp: December 31, 2016, 01:56:51 am
content: I have tested the outlets for wiring issues, and tried moving the scope to use different wall outlets around the house.The common variable seems to be that in rooms towards the front of the house - in view of a known RF mast some kilometers away - the signal is very strong. In other rooms towards the rear its only just detectable.

author: cdev
author_rank: Super Contributor
timestamp: December 31, 2016, 01:58:44 am
content: What you are seeing is FM radio, you can do the same with an RTLSDR (rtl2832 and r820t based USB TV dongle) and SDR software. (a poor man's spectrum analyzer) Your input is likely picking up a strong signal as it is intended to.

author: julian1
author_rank: Frequent Contributor
timestamp: December 31, 2016, 02:17:54 am
content: I've got a 820t2 currently serving a media center, but purchased with the intention of playing with SDR! Just never had the time to play with it yet.I wonder if higher MHz rated probes would provide better insulation? It's quite annoying in turning the trace into a thick band at much slower time divisions.

author: tggzzz
author_rank: Super Contributor
timestamp: December 31, 2016, 08:35:34 am
content: Quote from: julian1 on December 31, 2016, 02:17:54 amUnlikely.Set the 20MHz bandwith limit.

author: cdev
author_rank: Super Contributor
timestamp: December 31, 2016, 10:57:58 pm
content: You're seeing what is there, so your equipment is doing it's job.A small loop, say 5 cm is useful as an antenna for locating the source of nearby RF signals.

author: Gary350z
author_rank: Regular Contributor
timestamp: January 01, 2017, 02:22:59 pm
content: I get the local FM radio station (99.9MHz) on my scope, but at a much smaller amplitude.See my post here:https://www.eevblog.com/forum/projects/radio-stations-detected-on-oscilloscope/msg965930/#msg965930

author: cdev
author_rank: Super Contributor
timestamp: January 01, 2017, 08:58:46 pm
content: What's All This Scope Probe Stuff, Anyhow?The Bob Pease show.