RFI source finally identified! - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 7th Mar 2021, 6:41 pm

For at least a year I've been experiencing intermittent wideband RFI [on both 2M and the Band-II FM broadcast-band]. Attempts to track down the source were frustrating - it _seemed_ to originate somewhere in the house but could not be localised; turning off the mains at the breaker-panel didn't reduce it either.

Something to live with, I concluded. At least it was intermittent, only usually lasting for an hour or two.

Today I finally identified its source. I use a "Pebble SmartStick" external battery to top-up the charge in my phone between proper charges; seems that this contains a Li-Ion battery and a small 'boost' converter to lift the voltage to a USB-friendly 5V, and my interference issue was coming from this.

See below for a photo of the offender.

That I was using a 1-Metre-long USB cable to connect it to my phone certainly was not helping - I had inadvertently included a nice 1/2-wave-long 144MHz 'antenna' to help it radiate!

So now I know.

Kentode · 7th Mar 2021, 7:58 pm

I hope you opened the front door and drop-kicked it down the road!

G6Tanuki · 7th Mar 2021, 8:55 pm

I was thinking of donating it to one of my enemies!

7th Mar 2021, 9:05 pm

Quote:

I was thinking of donating it to one of my enemies!

I hope their neighbour isn't a radio user!

Herald1360 · 7th Mar 2021, 10:07 pm

An interesting challenge- could you shut it up by stuffing it in a die-cast box with some I/O filtering?

Is it noisy when it's being charged itself?

G6Tanuki · 8th Mar 2021, 4:23 pm

The metal case of the thing is already a spun-aluminium tube with a screw-on top, so it should be relatively well-shielded against radiation direct from the internal SMPS.

It doesn't radiate when being charged.

Can't be bothered to investigate it further - it ws a 'freebie' given out as part of a conference goodie-bag some years back so it's not as if I'll be losing anything if I just bin it.

greg_simons · 8th Mar 2021, 4:53 pm

Hmm, just got a couple of boost converters to play with, I'll keep an ear out for any spurious radiation!.
Greg.

G6ONEDave · 8th Mar 2021, 6:28 pm

It can be bad enough dealing with spurious interference from rf systems that are designed for rf use. It's another ball game sorting out designs that are not supposed to transmit rf interference in the first place. Well done in finding the culprit of the trouble! Maybe a friendly steam roller driver could run over the item for you.
Dave

agardiner · 8th Mar 2021, 6:38 pm

It just shows, you can't trust anything modern! Even batteries themselves!

G6Tanuki · 8th Mar 2021, 6:50 pm

Quote:

Originally Posted by greg_simons

Hmm, just got a couple of boost converters to play with, I'll keep an ear out for any spurious radiation!.
Greg.

That was, in part, one of the motivations for my posting this: I see regular forum discussions about charging- and using Li-Ion batteries to power things and as my experience shows, it's perhaps a bit more-complicated than at first meets the eye.

[My plan to build a Li-Ion based replacement battery-pack for my Clansman PRC320 is now very much on-hold!]

7th Mar 2021, 6:41 pm	#1
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	RFI source finally identified! For at least a year I've been experiencing intermittent wideband RFI [on both 2M and the Band-II FM broadcast-band]. Attempts to track down the source were frustrating - it _seemed_ to originate somewhere in the house but could not be localised; turning off the mains at the breaker-panel didn't reduce it either. Something to live with, I concluded. At least it was intermittent, only usually lasting for an hour or two. Today I finally identified its source. I use a "Pebble SmartStick" external battery to top-up the charge in my phone between proper charges; seems that this contains a Li-Ion battery and a small 'boost' converter to lift the voltage to a USB-friendly 5V, and my interference issue was coming from this. See below for a photo of the offender. That I was using a 1-Metre-long USB cable to connect it to my phone certainly was not helping - I had inadvertently included a nice 1/2-wave-long 144MHz 'antenna' to help it radiate! So now I know. Attached Thumbnails

7th Mar 2021, 7:58 pm	#2
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,301	Re: RFI source finally identified! I hope you opened the front door and drop-kicked it down the road! __________________ Regards, Ken. BVWS member

7th Mar 2021, 8:55 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: RFI source finally identified! I was thinking of donating it to one of my enemies!

7th Mar 2021, 10:07 pm	#5
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: RFI source finally identified! An interesting challenge- could you shut it up by stuffing it in a die-cast box with some I/O filtering? Is it noisy when it's being charged itself? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

8th Mar 2021, 4:23 pm	#6
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: RFI source finally identified! The metal case of the thing is already a spun-aluminium tube with a screw-on top, so it should be relatively well-shielded against radiation direct from the internal SMPS. It doesn't radiate when being charged. Can't be bothered to investigate it further - it ws a 'freebie' given out as part of a conference goodie-bag some years back so it's not as if I'll be losing anything if I just bin it.

8th Mar 2021, 4:53 pm	#7
greg_simons Octode Join Date: Jul 2004 Location: Evesham, Worcestershire, UK. Posts: 1,422	Re: RFI source finally identified! Hmm, just got a couple of boost converters to play with, I'll keep an ear out for any spurious radiation!. Greg. __________________ Picture, sound?, DOOR.

8th Mar 2021, 6:28 pm	#8
G6ONEDave Octode Join Date: Dec 2019 Location: Owston Ferry, North Lincolnshire, UK. Posts: 1,701	Re: RFI source finally identified! It can be bad enough dealing with spurious interference from rf systems that are designed for rf use. It's another ball game sorting out designs that are not supposed to transmit rf interference in the first place. Well done in finding the culprit of the trouble! Maybe a friendly steam roller driver could run over the item for you. Dave __________________ Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)

8th Mar 2021, 6:38 pm	#9
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Re: RFI source finally identified! It just shows, you can't trust anything modern! Even batteries themselves!