OT question about blocking interference

OT, but lots of radiation and etc experts here.
I'm a country (interior of Brazil) doc and use an ECG in the
local free state clinic, which avoids patients traveling 60 kilometers
or so to the nearest free hospital to get them done.
Recently, there has been a terrible amount of interference ,
making it almost impossible to do a readable ECG. So the manufacturers
took it back on the guarantee, and gave us a replacement, which also
did not work. Our original works fine at the factory.
So the problem is the locale, not the machine.
So I tried things like punching an earth straight into the
ground(no good), unplugging from the mains, and running on
batteries(no good either), and moving the patient and machine around.
And discovered that the clearer the view of the telephone companies'
retransmission tower, the worse the interference.
This tower probably transmits on wireless frequency,
cell-phone frequency, and maybe something in the way of bulk, as we
are between two major cities. It has a lot of drum shaped antennas all
around it's structure, pointing in various directions.
So I suggested that the ECG people find some way of protecting
from the radiation. Today the "solution" arrived, a nice big metal box
to put the ECG machine in. Of course it did not make any difference,
the machine is already shielded, it's the leads and the patient that
are not.
I thought of making some sort of screen to reflect the
radiation away, the same way a parabolic antenna will reflect wireless
to a dipole, but I have no idea on what material (mesh, sure, but what
size?), and it must be light, I might have to rush the machine and the
screen into another room if someone decides to have a heart attack.
Any ideas ?
TIA
PS, we noticed that the fatter the patient, the worse the
interference, does that make sense or is it a coincidence ?

On 4/7/2010 8:28 PM, Shadow wrote:
> OT, but lots of radiation and etc experts here.
> I'm a country (interior of Brazil) doc and use an ECG in the
> local free state clinic, which avoids patients traveling 60 kilometers
> or so to the nearest free hospital to get them done.
> Recently, there has been a terrible amount of interference ,
> making it almost impossible to do a readable ECG. So the manufacturers
> took it back on the guarantee, and gave us a replacement, which also
> did not work. Our original works fine at the factory.
> So the problem is the locale, not the machine.
> So I tried things like punching an earth straight into the
> ground(no good), unplugging from the mains, and running on
> batteries(no good either), and moving the patient and machine around.
> And discovered that the clearer the view of the telephone companies'
> retransmission tower, the worse the interference.
> This tower probably transmits on wireless frequency,
> cell-phone frequency, and maybe something in the way of bulk, as we
> are between two major cities. It has a lot of drum shaped antennas all
> around it's structure, pointing in various directions.
> So I suggested that the ECG people find some way of protecting
> from the radiation. Today the "solution" arrived, a nice big metal box
> to put the ECG machine in. Of course it did not make any difference,
> the machine is already shielded, it's the leads and the patient that
> are not.
> I thought of making some sort of screen to reflect the
> radiation away, the same way a parabolic antenna will reflect wireless
> to a dipole, but I have no idea on what material (mesh, sure, but what
> size?), and it must be light, I might have to rush the machine and the
> screen into another room if someone decides to have a heart attack.
> Any ideas ?
> TIA
> PS, we noticed that the fatter the patient, the worse the
> interference, does that make sense or is it a coincidence ?

Too much I don't know on this subject to give any good advice. But, let
me throw out some far-out ideas, and maybe others will pick up on them
and help you weed out the bad from the impossible.

Are you sure the leads aren't shielded? If not -- how involved would it
be to shield them? This is something you would probably need the
guidance of the EKG manufacturer on, but maybe replacing the leads with
light weight coax, and some means of grounding the shield to the EKG
machine might just do it.

Probably it is safe to assume the interference is getting into the
machine via the leads. I don't know what frequencies are involved with
the desired signals from the patient, but I suspect they are much lower
than what the cell tower is putting out. How about slipping ferrite
beads over the leads at the machine end? They become much more
effective as you go up in frequency. There are lots of different mixes
the beads are made from -- if you could guess at the frequencies
involved, possibly one of the manufacturers of ferrite materials could
give you some help.

If you were always working in one room, then you could try to shield the
entire room. I guess copper screen would be a good material, but maybe
cheaper to try would be aluminum foil. Maybe you don't need to do the
entire room -- just the side toward the tower might be enough.

You could try to make a portable screen -- like the privacy screens that
were like three frames hinged together -- and use copper or aluminum
screen on them. Might work, and could be moved around easily.

Shielding an entire room, and doing it right, is not an easy job. I
would try to work closer to the EKG machine first, and see if you can
tame the situation that way.

Can't offer any suggestions on the size of the patients! I assume
spraying them with aluminum paint is out of the question :-)

....Bob

On Wed, 07 Apr 2010 21:26:40 -0400, Bob K <(E-Mail Removed)>
wrote:

>Can't offer any suggestions on the size of the patients! I assume
>spraying them with aluminum paint is out of the question :-)
People out here are +- lazy. It would probably take me 48
hours to hire a painter. Aluminum paint would take longer to find. My
last patient had a massive anterior left coronary artery infarction,
he was in a hurry ....
As to using smaller patients, I have it a thought, but it's
the big fat ones that insist on getting trying to die. Patients here
to not believe in following the rules.
Humor aside, I will study your suggestions, also "who
where"'s. Tomorrow, it's too late ATM.

TY

Shadow wrote:
> OT, but lots of radiation and etc experts here.
> I'm a country (interior of Brazil) doc and use an ECG in the
> local free state clinic, which avoids patients traveling 60 kilometers
> or so to the nearest free hospital to get them done.
> Recently, there has been a terrible amount of interference ,
> making it almost impossible to do a readable ECG. So the manufacturers
> took it back on the guarantee, and gave us a replacement, which also
> did not work. Our original works fine at the factory.
> So the problem is the locale, not the machine.
> So I tried things like punching an earth straight into the
> ground(no good), unplugging from the mains, and running on
> batteries(no good either), and moving the patient and machine around.
> And discovered that the clearer the view of the telephone companies'
> retransmission tower, the worse the interference.
> This tower probably transmits on wireless frequency,
> cell-phone frequency, and maybe something in the way of bulk, as we
> are between two major cities. It has a lot of drum shaped antennas all
> around it's structure, pointing in various directions.
> So I suggested that the ECG people find some way of protecting
> from the radiation. Today the "solution" arrived, a nice big metal box
> to put the ECG machine in. Of course it did not make any difference,
> the machine is already shielded, it's the leads and the patient that
> are not.
> I thought of making some sort of screen to reflect the
> radiation away, the same way a parabolic antenna will reflect wireless
> to a dipole, but I have no idea on what material (mesh, sure, but what
> size?), and it must be light, I might have to rush the machine and the
> screen into another room if someone decides to have a heart attack.
> Any ideas ?
> TIA
> PS, we noticed that the fatter the patient, the worse the
> interference, does that make sense or is it a coincidence ?

To be sure simply take a couple of dividing screens and line with some
aluminium foil , place the screen between the tower and the patient ,
does it improve ?

You have two choices one being move from line of sight of the tower or
build a Faraday room or both

the phone tower might have an accident but I cant suggest that
good luck

Shadow wrote:
> OT, but lots of radiation and etc experts here.
> I'm a country (interior of Brazil) doc and use an ECG in the
> local free state clinic, which avoids patients traveling 60 kilometers
> or so to the nearest free hospital to get them done.
> Recently, there has been a terrible amount of interference ,
> making it almost impossible to do a readable ECG. So the manufacturers
> took it back on the guarantee, and gave us a replacement, which also
> did not work. Our original works fine at the factory.
> So the problem is the locale, not the machine.
> So I tried things like punching an earth straight into the
> ground(no good), unplugging from the mains, and running on
> batteries(no good either), and moving the patient and machine around.
> And discovered that the clearer the view of the telephone companies'
> retransmission tower, the worse the interference.
> This tower probably transmits on wireless frequency,
> cell-phone frequency, and maybe something in the way of bulk, as we
> are between two major cities. It has a lot of drum shaped antennas all
> around it's structure, pointing in various directions.
> So I suggested that the ECG people find some way of protecting
> from the radiation. Today the "solution" arrived, a nice big metal box
> to put the ECG machine in. Of course it did not make any difference,
> the machine is already shielded, it's the leads and the patient that
> are not.
> I thought of making some sort of screen to reflect the
> radiation away, the same way a parabolic antenna will reflect wireless
> to a dipole, but I have no idea on what material (mesh, sure, but what
> size?), and it must be light, I might have to rush the machine and the
> screen into another room if someone decides to have a heart attack.
> Any ideas ?
> TIA
> PS, we noticed that the fatter the patient, the worse the
> interference, does that make sense or is it a coincidence ?
Hi,
This comes to mind. You build a room which is enclosed with grounded
metal plate walls and ceiling which ECG machine and patient can
use. I worked once radiation proof military computer system which was
installed inside a metal wall/ceiling surrounded room. This room was
grounded well and even door was triple metal chamber.

"Shadow" <Sh@dow> wrote in message
news:(E-Mail Removed)...
> OT, but lots of radiation and etc experts here.
> I'm a country (interior of Brazil) doc and use an ECG in the
> local free state clinic, which avoids patients traveling 60 kilometers
> or so to the nearest free hospital to get them done.
> Recently, there has been a terrible amount of interference ,
> making it almost impossible to do a readable ECG. So the manufacturers
> took it back on the guarantee, and gave us a replacement, which also
> did not work. Our original works fine at the factory.
> So the problem is the locale, not the machine.
> So I tried things like punching an earth straight into the
> ground(no good), unplugging from the mains, and running on
> batteries(no good either), and moving the patient and machine around.
> And discovered that the clearer the view of the telephone companies'
> retransmission tower, the worse the interference.
> This tower probably transmits on wireless frequency,
> cell-phone frequency, and maybe something in the way of bulk, as we
> are between two major cities. It has a lot of drum shaped antennas all
> around it's structure, pointing in various directions.
> So I suggested that the ECG people find some way of protecting
> from the radiation. Today the "solution" arrived, a nice big metal box
> to put the ECG machine in. Of course it did not make any difference,
> the machine is already shielded, it's the leads and the patient that
> are not.
> I thought of making some sort of screen to reflect the
> radiation away, the same way a parabolic antenna will reflect wireless
> to a dipole, but I have no idea on what material (mesh, sure, but what
> size?), and it must be light, I might have to rush the machine and the
> screen into another room if someone decides to have a heart attack.
> Any ideas ?
> TIA
> PS, we noticed that the fatter the patient, the worse the
> interference, does that make sense or is it a coincidence ?

I'll take your last quarry first. There *is* a possibility of a correlation
to the size of the patient but without much more data anything I said would
be pure speculation.

First equipment manufactured for the US market is not required to be
hardened to interference the only requirement is that it does not cause
interference to other equipment.

Equipment manufactured for the EURO market does and is required to be
certified with a logo CE { see
http://ec.europa.eu/enterprise/polic...pean-standards } on the device.
Equipment manufactured under that certification are typically much less
susceptible to external interference. (the solution in the US seems to be to
post signs 'turn off cell phones'

Without knowing the system frequency bands and the modulation modes on the
tower I'm going to have to guess on the proximate cause.

Bit of back ground TDMA/GSM (pulsed), them analog, the CDMA is the order of
potential interference. Some may suggest the microwave links could have an
influence but in my experience (near 50 years -- some in designing medical
instrumentation) the power levels and the fact that most microwave links are
highly directional that is an unlikely source.

Going back to my experience at a teaching/research facility (mid 60's) we
had a problem with marine radar (this was New Orleans and blocks from the
Mississippi River)

We employed two approaches. First was shielding the device and second was
using ferrite beads on the sensor leads as they entered the box. This works
because the ECG data are typically composed of signals with components below
200Hz were as the interference is many magnitudes higher. That said I
cannot assure that the use of the beads will not modify the signal data.
It's very unlikely but something you should be aware of since life is at
stake.

Also I'm working based on what you posted there may be other elements that
neither you nor the group are aware.

A screen room would be the ultimate but would greatly limit the usefulness
of your equipment.

If you have more questions post to the group or if the data is confidential
you can reach me back channel at brother_rabbit @ hotmail.com (remove the
spaces)



http://en.wikipedia.org/wiki/Ferrite_bead

http://computer.howstuffworks.com/question352.htm

Not making a recommendation just a link to one source

http://www.palomar-engineers.com/Fer...ite_beads.html