Cell Phone Interference

Interference is possible and difficult to perdict in advance. I have not personally seen a "hospital approved" advertised cell phone and would not know what to expect in same. Perhaps there is some other aspect besides RF interference that they are complying with?

FYI - There is (was?) a magazine called "Compliance Engineering" that routinely reported on RF interference to unintentional "receivers". A classic case is motorized wheel chairs being interfered with by taxi cab radios. In another case (documented!), a patient died in the Operating Room because of a P5 or P6 VHF Paging Transmitter located on the rooftop. Later analysis concluded the paging transmitter was not malfunctioning and the problem was traced to conducted interference. (Not all of the O/R Suite equipment was battery operated.)

That said, beware of "spin". I'd be curious to see the ad.

-mpm

These phones are bigger, and yellow and black here. Look more like a portable house phone.

By the way, I wish they made some SMALL portable house phones.

I'll try to search for those hospital phones some more.

There is an area here where they put up signs warning of any RF device. The manufacturer of some very important equipment made that suggestion after failure of said important system. Seems like they need a better design.

greg

A long while back, a researcher requested the pager antenna be moved from his room area. The antenna was probably about 25 feet away. It obviously made some interference. I have known cars to malfunction driving near a TV tower. Seems like things are much better. On a British TV show they zapped a car with artificial lightning, and it did OK.

greg

I did find some info. There appears to be very similar to portable cell phones, but the power level appears to be 100 mw or less.

Phones by Spectralink

greg

There was a lecture hall in college in a building adjacent to a main thoroughfare. The wireless microphone system in the room would pick up the taxi cabs if they keyed up just as they whizzed by... :-)

Back in high school days, there was this Ham opperator, a woman, using 1000 watts on 6 meters, on the military freqs, well she was heard for miles around, I think it was every Sunday night. Everybody used outside antennas back then. Gracy K3JTH

greg

Did anybody talk to her about it? Usually, hams are very concerned with interference - I've even heard of hams who, when their neighbors complained about picking him up on their TVs, _GAVE_ them filters to filter his signal out of their cheap TV front ends, and came over and installed them!

Cheers! Rich

Don't remember exactly, but her affiliation as a Mars radio station probably gave her some immunity. U.S. ARMY MILITARY AFFILIATE RADIO SYSTEM

greg

I wasn't going to bring up all the weird things I've seen (I used to have a high-profile job dealing with lots of towers in the US)...

I recall one episode where a music teacher was teaching students on her piano. She called in complaining she could hear music coming out of her piano. (Duh!??) (At first, I couldn't figure out what she was talking about until it dawned on me she had a digital piano!) Of course, she was in a blanketing contour and the audio she was hearing was coming from an FM on the tower. I don't think the station ever resolved the problem. She was late reporting it, and they were under no legal obligation. (This was from an FM upgrade in power)

Another guy swore up and down our tower was causing interference to his TV reception. (The tower was completly empty - no tenants - no antennas!!) I asked him to send me a video of the interference. After which, I suggested he call the local power company and get the pole transformer replaced! (That fixed it.) I understand this is a big problem with low-band hams, like broadband over power lines promises to be...?.

And then you have the truly weird ones... A paging operator calls me up and says they can't receive a GPS signal at the tower. (Which is unusual to say the least. ...weird because there's clear view of the sky and this particular complaint had "never" came in before. (Trust me, we heard 'em all.) And besides, you could pretty much guarantee the GPS satellites were working!) But the tech swore it was "us".

Sure enough, a low-power TV station on an adjacent tower had removed their 2nd harmonic filter. I forget exactly which channel, 47 I think? (We didn't own the station.)

Reinstall filter, slap engineer on wrist, "Don't do that again!". Problem solved.

Next time, I'll tell you about the kitchen sink (actually a metal frame base slop sink) at an AM station that was causing interference

200 miles away! We were really lucky to find that one. Had been going on intermittently for years. I didn't find it myself, but I understood the problem was so unbelievable (and yet definitely repeatable), that the whole sink was unbolted, packed up and shipped off to the engineer in charge at the affected FCC monitoring point. True story.

So "Yeah", if someone tells me they have a "Hospital Approved" cell phone, I'll listen. If a bit skeptical. -mpm

...OK just one more, 'cause this one is just too damned funny!!

Customer calls in saying the shelter is "nuclear hot" inside. Air conditioner is running, but not blowing cold.

So we get out there to find an old, busted A/C compressor. We get that replaced, and about a month later someone else calls in with the same complaint.

This time though, it looked like some livestock had kicked or knocked over the compressor. This was at an AM station, which are notorious for lack of metal fencing. So we built a nice, solid wooden fence around the (now new) compressor. If you're counting, this is Compressor #2.

Several weeks go by and sure enough, the call comes in again. Only this time, the tech on the other end says the wooden fence is all busted up and he's actually witnessing a bull HUMPING the A/C compressor!!!

Needless to say, compressor #3 went on the roof !!

-mpm

It shouldn't, but then again, I've taken note of your earlier comment, "on the military freqs" - if it was actual military stuff, they probably just didn't give a shit.

Thanks, Rich

That is also the the way legisltion and regulation also read; if your gizmo is important, it had better be hard to interfere with. Just the same incorrect installation may ruin everything.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

Scam? I doubt it. I can pick up GSM cell phones signaling over FM radios from several yards distance.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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Used to entertain myself with the 900 mhz radio and teenagers' cheap radar detectors back when I was driving a cab. Hitting the talk button lit up their detectors. Always good for a chuckle when they slammed on their brakes at 80 mph.

Then it is, by definition, a poorly designed radio receiver. Being disrupted by relatively moderate emissions at 8 or 19 times the normal receiver operating frequency is clearly an inferior design.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

The cellphone here is the prime suspect for a weird thumping the TV set is doing occasionaly (sounds like its power supply does something, several thumps over 3-4 seconds, once a day or so if the phone is at the TV's table). I don't have the statistics on that so I could not swear it is the cellphone, but it has not done it for a week or two since the phone is not put there and it has never done it before without the phone there. What would the phone transmit once a day or so I don't know. It does not interfere with the TV during normal communication, this must be talking to some more remote location. Losing the local station shortly and trying to get in touch with another? Transmitting compressed data it has gathered over the day? Anyones guess :-).

Dimiter

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Typical cell phones are in communication with the base station even when you are not using the phone for conversation. This is how the cell phone company "knows" which cell you're on in case you are moving. (They do not ring every cell tower in the world. That would be a waste of spectrum.)

There are "channels" for signalling, and "channels" for voice communications. If nothing changes, your cell phone might stay on a single signalling "channel" for weeks. But...

If your phone experiences a fade, or loss of signal, the reacquisition may occur on another signalling "channel". (This can, and does, often happen many times a day.) It can also happen if the cell site transmitter drops the channel, or if they dynamically reallocate spectrum to deal with cell site congestion issues, etc...

The point is, when your cell phone (lying peacefully on the TV table) needs to get updated, it will broadcast a short burst of data back to the serving cell site. This is probably what you are experiencing (TV Interference) when the phone is not in Communication.

To extend this reasoning, when you are talking on the phone, First, you are using a different "channel". One other than the Signalling "channel", but very likely in the same general band. But many things have changed. The orientation to the TV for one thing. (Presumably you are further away unless you put your ear on the TV table?) Also, the cell site may have instructed the cell phone to reduce output power on the voice channel, etc...

Unintentional receivers in close proxmity to cell phones and the like are usually bombarded with fairly high RF signal strengths, which their front ends were not designed to deal with. While it is certainly possible to make receivers that would be immune to this proximity effect, it is not often economical, and may impose physical size restrictions (for the front end filtering) which consumers could find objectionable. In short, you just have to live with it.

BTW, I offset the word "channels" in quotes because in the strictest sense, not all cellular systems (air interface standards) use discrete channalized bandwidth, but the intent should be clear from the above.

-mpm

hey

re

Probably front end overload, or direct radiation in the receiver IF sections.

Thanks for your cellphone behaviour analysis.

that's a viable guess, could be the cellphone is trying to talk louder to reach some more distant station. I have not watched its reported signal strength when this happens, I may still do it. Could also be many other things, of course.

Quite unlikely, the area is not densely populated and it also happens during the night when most people are asleep.

No, this can be ruled out. When the phone gets messages and is at that table there is no interference. I doubt it uses a different power level to acknowledge messages. Also, it does not drive the TV mad when it rings.

It is not the front end. It is, like I said, the TV power supply (switched). The thing (the whole TV set thumping madly) happens even when the power is "off" (on enough to see the remote control and to be messed up by the phone), the signal power from the phone must be orders of magnitude higher than it is during normal transmission to achieve that.

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