[RFI] Air Cleaner Interference

John Wagner jwagner at dxengineering.com
Thu Sep 29 17:03:27 EDT 2005

Jim wrote: 
I just had an unusual interference problem that I want to share with the

I just bought a Honeywell 'desktop' HEPA type air filter that also included
an ionizer option.  It's pretty small and was just what I needed for my
computer/radio room.

I had it running about a day and noticed the red light which meant the
filter needed to be cleaned would blink once a second or so but would not
stay on solid red.  According to the manual, solid red would mean the filter
needed to be cleaned.

The first evening I had it in the room, I turned on the radio and heard this
repetitive impulsive noise and noticing the sky was very cloudy, I just
assumed this was precipitation static from the oncoming storm.  I always
disconnect my antenna outside and then turn off the radio during a storm.
Sure enough about an hour later we had a lightning storm and I thought
nothing more of it.  

I have heard precipitation static build up before a storm and since there
was a storm later, I thought I had the problem identified. I do remember
being a little puzzled as usually the precipitation noise will increase the
rep rate until there is a particularly strong impulse and the process will
start over getting faster and faster until a large discharge.  This one was
unusual in that it was more consistent.

This morning I plugged the antenna back in and turned on the radio and here
was the impulsive noise again!  The noise blanker took care of it but it was
clearly something local.  Walking around the house/yard with my R-10 tuned
to 19 MHz convinced me it was coming from my house.   I have horizontal loop
and also a vertical dipole in the attic and the vertical had a much stronger
signal.  I then walked around the rooms of my house with my R-10 and nowhere
in particular made the noise louder.  I was checking all of the gear in my
room and then checked the new air filter.  I was about to leave it as the
noise level was the same as everywhere else when I happened to notice the
red light would flash every time I heard the impulsive noise.  Turning off
the UV option on the filter made the noise go away!

The UV option, or what ever it was they were using to 'purify' the air was
the culprit.  It was most interesting the noise was not stronger right by
the unit nor did it show any apparent polarization.

I took the unit back to the store this afternoon and went back to a larger
HEPA filter which has no 'air purifier' built into it.  It's working fine

73's for now

Jim  K5QQ

I would suspect they are using an ionizer that produces ozone by some kind
of spark! Probably feeding down the ground system of the house power.

73 John

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