GSM-only interference [Telecom]

On Sat, 22 Aug 2009 09:16:21 -0400, Michael Grigoni wrote: .....

If a disease-carrying mosquito bites you on the face you will probably feel it compared to if it bites you on the back, but you still have the same chance of being affected/infected by the bite - it is just one area of skin is more sensitive than the other.

If you notice a GSM phone interfering with something because of the noticeable modulation pattern and you do not notice another type of transmitter interfering with the exact same equipment because its interference pattern is different, chances are the equipment is still being affected by both devices - especially if the interfering power levels and frequencies are similar.

In article ,

Better shielding of the 'affected' devices *IS* the answer.

Just curious: how does one retrofit shielding into affeected hearing aids and other implanted medical appliances as was mentioned in the 1994 article from the comp.dcom.telecom archives and recently reposted by me?

Google search just now didn't find it, so I uploaded the article here:

The article claims GSM's interference problems were suppressed until after GSM's rollout.

If the manufacturer didn't build the device correctly in the first place, _who's_ fault is that?

FCC rules are _very_ explicit on the matter -- if a device is affected by a _properly_operating_ transmitting device, the 'problem' *is* in the device that is being affected.

If the device isn't 'repairable', the option then is to _replace_ it with one that is properly shielded. It is solely the problem of the user of the affected device. So says the (*long* established) law.

Retrofitting to ameliorate poor design is difficult. Implanted medical devices are especially problematical.. you probably have seen signs near microwaves, antitheft gates, etc. warning pacemaker users. I suppose you could wrap yourself in aluminum foil, but that's not attire suited for all social occasions.

Fortunately, cell phones don't seem to affect implanted hardware much. It might be that the surrounding tissue provides shielding for the implanted device, or maybe those devices are not actually very sensitive to interference.

Dave

Well, *only* the GSM phones generate a data patten resulting in an envelope wave-form that in the audio spectrum.

That does *NOT* mean that RF from other phones, or other RF-emitting devices, is not getting into the same devices -- just that you don't "hear" it as 'sound'.

You appear to be an RF engineer -- do the following:

Pick an intercepted signal strength level.

Calculate the radius away from a 600 milliwatt transmitter where the intercepted signal will decline below that level.

Repeat that calculation for a 900 kilowatt ERP television transmitter.

Or a 3-5 megawatt aviation radar.

Now, for the 'hard part' -- explain why GSM is 'so much more unsafe' than those other emitters.

Per the information in the 1994 comp.dcom.telecom article, it can be argued that GSM cell phones are inherently flawed. To wit (from the article):

" 1. General R/F pollution. Any system that switches its R/F " transmitter on and off rapidly (GSM does it 217 times a second, TDMA " does it 50 times) will scatter EMI throughout the adjacent radio " spectrum. And the sharper the edge of the switch power (on and off), " the wider the band of hash it scatters. These sets need a 3-5MHz " guard-band between them and analog AMPS channels,and they try to ramp " up the power, and still they scatter crap into nearby television " broadcast bands. We've never had anything that generates EMI like a " GSM handset before in these bands. We need large numbers of them like " we need a hole in the head. " " 2. Audio-Hz interference. The on-off cycle of transmission power will " be read by any analog circuit nearby (with any rectification or " asymmetrical circuits) as an intrusive audio tone of 217Hz, and the " two major harmonics above. This buzz intrudes into hearing aids at " distances up to 30 metres, and is often intolerable at 2 metres. It " also gets into cassette recorder, wireline systems, and into modems as " a carrier tone.

I don't see how anyone can justify the above two items as being "normal", especially since a GSM cell phone can be transmitting at up to 2 Watts.

The 1994 article concluded:

" The real problem with both GSM and American TDMA is the way in which " all these problems were kept secret, and the systems were rolled out " slowly and quietly without anyone admitting problems until the press " started shouting. When they play these sorts of games, they have only " themselves to blame when the press reacts strongly and shouts 'foul' " especially when it is likely to be hearing-impaired people who suffer " in office environments. " " Later, problems were reluctantly admitted, but always the admission " was associated with "Don't worry, well fix it!" which is just another " of their lies. Most of these problems are intrinsic in time-division " power pulsing. " " More recently the tactic has changed once again: now they blame the " lack of shielding on hearing-aids and other electronic equipment, and " want to boost the standard of immunity, rather than reduce their own " emissions. " " It's the smoke-stack blaming inefficiencies in gas-masks for the " problems. ETSI is its own worst enemy.

Are you disagreeing with the above?

Interesting deduction, but true, in the microwave arena for GTE's Electronic Defense Labs back in the 1960s before computers completely caught my fancy and I left to join a computer startup (Tymshare).

Ever wonder why the first commercial microwave ovens were named the Amana Radar Ranges? The story as related to me at White Sands Missile Range was the discovery that jackrabbits and other critters downrange of our RADARs were being crispy-cooked by the microwaves.

GSM cell phones pumping out up to 2 Watts splattered across the spectrum does not sound (no pun) good to me. Interfering hearing aids is not a friendly act.

I am simply curious why such a noise emitter was approved by the FCC.

Vocabulary and phraseology _do_ give significant clues to training/background :)

"Revisionist history", I'm afraid.

Facts: Raytheon came out with a unit *using* the 'Radarange' name, almost exactly _two_decades_ before Amana built their first unit. Their first 'commercially successful' commercial units date from the mid 50's.

The "Radarange" name came from an employee naming contest, circa 1946.

Amana built the *second* 'home use' microwave oven -- the first "commercially successful" one. (Tappan built the first "home" units, more than a decade earlier.)

Amana does have the bragging rights for "the world's first" 115V, countertop microwave. Units prior to that needed 220V and were comparable in size to a full size stove.

See: for the 'real story' of the discovery of microwave cooking/heating.

You suppose that Amana's entry into the microwave oven business might have anything to do with the detail that Raytheon had recently bought them to get a retail distribution channel?

R's, John

I'm not surprised. As the "new" (and youngest) guy in the labs, I was often told stories that seemed credible to me at the time. :-)

But they respected the fact I was the only lab engineer with a certified soldering certificate and who also could make microwave receivers work by just waving my hands over them and moving stuff around that doesn't resemble anything looking like electronic parts. :-) And noone else there could coax a TIXM103 transistor into flat operation across the L or S bands for space apps.

Thank you! It's funny, for decades I was reluctant to buy a microwave oven due to concerns about the seals, and I ended up buying an Amana Radar Range about 15 years ago and it still works fine today.

Because the FCC does whatever Congress tells it to do, and Congress does whatever cellphone companies tell it to do.

How do you think we got the ECPA?

--scott

The whole SMECC site is a fascinating example of an online museum (even if there's a "pack-rattish" character to the whole site, and the HTML aspects of it are amateurish. Tons of great stuff there!

Is there also a real, physical museum associated with it? Anyone ever been there?

L band was 1-2 GHz and S band was 2-4 GHz.

Following is a short anecdote that perhaps should be preserved for posterity.

When I began working in that field, GC or GCPS was the common way to express giga cycles per second (now GHz).

Some people resisted the change to Hz from CPS, and one colleague had a reasonable argument for maintaining the status quo.

If the goal was to honor someone, why not honor Charles Proteus Steinmetz and we'd get to keep CPS instead of changing to Hz.

Food for thought. :-)

On Fri, 28 Aug 2009 00:18:00 -0400, Thad Floryan wrote: .......

You have to be joking, a 800MHz carrier digitally modulated at a few hundred hertz "splattering"?!?

Sit down and work out the spectrum use and then have a think as to why the technology actually works with thousands of handsets in simultaneous use at a busy base station.

I reckon there were very good reasons as to why this particular technology was approved for use in the US as well as virtually every other place on the planet.

It's affecting a lot of things including, as was posted here yesterday, [one model] of [stove] causing [it] to turn on [the oven] to a HIGH setting.

The 1994 comp.dcom.telecom article mentioned the interference to TV also. If you need to reread it:

No one is claiming GSM using TDMA doesn't work; it obviously does. However, had CDMA instead of TDMA been chosen, the interference problem would NOT exist. TDMA is powering ON/OFF the transmitter 217 times a second.

An interesting and not too technical comparison of CDMA and TDMA is here:

Yes, the Feds didn't understand it. An interesting article from 1996 here:

Should have gone CDMA (which will occur in the future).

And as stated in the 1994 comp.dcom.telecom article:

" The real problem with both GSM and American TDMA is the way in which " all these problems were kept secret, and the systems were rolled out " slowly and quietly without anyone admitting problems until the press " started shouting. When they play these sorts of games, they have only " themselves to blame when the press reacts strongly and shouts 'foul' " especially when it is likely to be hearing-impaired people who suffer " in office environments. " " Later, problems were reluctantly admitted, but always the admission " was associated with "Don't worry, well fix it!" which is just another " of their lies. Most of these problems are intrinsic in time-division " power pulsing. " " More recently the tactic has changed once again: now they blame the " lack of shielding on hearing-aids and other electronic equipment, and " want to boost the standard of immunity, rather than reduce their own " emissions. " " It's the smoke-stack blaming inefficiencies in gas-masks for the " problems. ETSI is its own worst enemy.

....... "Splattering" is a specific term of transmitting on frequencies not intended - usually due to poor design or overload of a RF transmitter - it has nothing whatsoever to do with GSM transmitters interfering with devices susceptible to RF.

As has now been stated in forum previously, ANY device transmitting at those same frequencies will cause interference to devices that just happen to be noticeable because of the GSM modulation. The actual nature of the interference will depend on many factors, but if a device picks up the RF from a GSM transmitter, it will pick up the RF from any other transmitter (using the same frequencies).

A non-GSM transmitter could well shut down a susceptible device in a way that may not be apparent, and not immediately knowing that the device is being interfered with could be far more of a problem than the obvious GSM interference.

Which is better, a hearing aid silently shut down by an interfering transmitter or a GSM buzz? If you were a deaf person about to cross the street on the assumption that you would hear a car horn would you prefer silent interference on your obviously faulty device?

The bottom line is that there will still be interference, but GSM interference is more noticeable.