OT question about blocking interference

Google for Faraday cage. There are a lot of industries that require effective RF screening, and this is the real answer.

There are FC's and FC's, of course. Some are built like a coldroom, with every service (power, air etc) going in through a filter, and there are those that are a far simpler design. The difference is the target reduction in RF levels. The serious ones we used were the coldroom style, as we needed to see all RF products that our spectrum analysers were capable of detecting.

In your case, a less ambitious target - say a 30 or 40dB reduction - would probably provide you with more than adequate signal/noise levels. This may take the form of a "room" with wire mesh on all sides (and don't forget the floor). I have seen them built using bronze flywire mesh. The key is the size of the mesh aperture in wavelengths at the highest likely interfering frequency - a *maximum* of 1/4 wavelength will introduce significant attenuation, smaller is better but going much below 1/10 wavelength produces rapidly diminishing returns. Don't know Brazil's cellphone systems at all, but I'd work on Fmax is around 2100MHz so a wavelength is 14cms.

This may all sound like a lot of trouble, but it is a fairly safe bet that the ECG manufacturer has already put as much filtering on the leads as he can without compromising efficacy.

As you noted, this enclosure needs to house the entire setup - patient, leads, equipment - and your power system for the machine needs to be either filtered at the entry point or btery within the enclosure.

Bigger receiving antenna?

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

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

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-

The problem is the machine. If properly designed, it would have sufficient shielding and filtering to prevent interference from causing the malfunction. Clearly it is the design since its replacement has the same susceptibility.

It is possible the interference is actually caused by cell phones rather than signals from the nearby tower. Try turning off all wireless devices (WiFi routers, laptop computers, cell phones) and see if the problem is reduced.

As others mentioned, a screen room (Faraday cage) would likely provide shielding. To make or buy one would be somewhat expensive, and would limit the portability of your equipment.

A better solution would be to have the manufacturer come to your location and work with you to install any needed shielding and filtering. It should be relatively simple to design a low pass filter that would not affect the ECG signals, but would reject all radio/microwave signals that might be in the environment.

The manufacturer should be interested in solving the problem. Such a sensitive machine is likely to respond to the mere presence of cell phones (which are continuously transmitting even when not being used). They would be libel for any injury that might occur to a patient who suffered as a result of the machine's inability to perform.

Fred

So if I have a slow leak in my tire, and take it to the garage, but their tire machine won't work with my tire, and on the way home, it blows out and I cause a huge accident, the garage and tire machine mfg are liable ?

As part of a jury, I would never vote against the company for either situation above....nor would I ever award a verdict to person injured during the commision of a crime....nor would I ever make an award for injury on property that wasn't *truly* the owners fault....some retard falling down my front steps and injuring themselves is just that....a f'n retard. Now if the steps were wood and rotting, and I knew about it, and the step collapsed because I didn't fix it, that may be something different.

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.

consider something like a faraday cage big enuf to put a bed/couch in (metal mesh screening) if you have it in an office... want something portable? How bout an aluminized mylar "space blanket"/metal impregnated fabric/metalalized tarp with a grounding strap/clip/lead/etc, that can be carried around, and thrown over the patient... no reason you can't do both, one in an office and one for portable use

can't imagine why the weight of the patient would matter

be carefull that the leads themselves are sheilded too (actually the wires between the patient and the machine, not sure what to call the wires between the things on the patient and the machine), wouldn't do to have them picking up interference

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

} 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)

Not making a recommendation just a link to one source