Cellphone interference?

Chuck,

I worked on the battlefield cell phone contracts. They were quite a bit stronger than what we carry around. They also had their own frequencies and portable cell towers. Could this be what you read?

Cell site ERP can be up to 500W

"At a cell site, the total RF power that could be transmitted from eac transmitting antenna depends on the number of radio channel (transmitters) that have been authorized by the Federal Communication Commission (FCC) and the power of each transmitter. Although the FC permits an effective radiated power (ERP) of up to 500 watts pe channel (depending on the tower height), the majority of cellular site in urban and suburban areas operate at an ERP of 100 watts per channe or less.

An ERP of 100 watts corresponds to an actual radiated power of 5-1 watts, depending on the type of antenna used. In urban areas, an ERP o

10 watts per channel or less is commonly used. For PCS cell sites, eve lower radiated power levels are normally used. As with all forms o electromagnetic energy, the power density from a cellular or PC transmitter rapidly decreases as one moves away from the antenna Consequently, normal ground-level exposure is much less than th exposure that might be encountered if one were very close to th antenna and in its main transmitted beam. Measurements made nea typical cellular and PCS cell sites have shown that ground-level powe densities are well below limits recommended by RF/microwave safet standards used by the FCC."

-- Lomceva

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Not the best of flying conditions either way. Especially for such a model as that one. And I think that was the real point!

Maybe! But as I recall, the impression I received at the time was that it referred to commercial products. Either way, technology marches on and what was standard yesterday is not standard today which in turn will disappear before tomorrow.

I think both of you are both right and wrong. The cell tower communicates with the cell phones at the same signal strength, if it did not then it would transmit futher than the cell phones and interfer with phones in adjacent cells. However cell towers have a stronger radion on differant frequencies to transmit and relay the phone messages to a central station where they are converted to landline or microwave transmission. I believe the max power for GSM phones is one watt TDMA and analog (which use the same analog cell system) use up to

3 watts. Not enough to bring down planes nor fry computers or brains but just my opinion.

Since we seem to disagree, I don't see how that can be the case.

That's simply not true.

Cellsites have much better receive antennas than mobiles. Therefore they can receive lower power signals.

It depends on the system architecure, but the cellsite might also have full diversity receiver (dual-antenna/dual-receiver) hardware to combat rayleigh fading. Some systems divide the cell up into "sections" by the use of high gain directional receive antennas.

Cellsites can afford to spend more weight/power on receiver circuitry in order to make it better able to detect and descriminate low-power signals.

Cellsites also have separate rx/tx antennas which allows the receiver to avoid be desensitized by the transmit signal.

All of this means that the cellsite can receive signals at much lower power levels than a mobile can.

Mobiles transmit at 1/10 to 1/100 of the power level transmitted by a cellsite.

There may be a microwave link to a switch. Those links are generally have a very narro beamwidth.

Cellsites transmit at up to 100W. 10-30W is probably more typical.

My referance is the strength of the cell phone. If the cell tower is that much stronger than the cell phone, how is interferance from cell phones in nearby cells avoided? I know the channels skip cells so that that cannot happen to the adjacent cell, but with that much power I would think that a cell phone could pick up the cell tower transmission from two or more cells over.

I believe the microwave link is at a central cell tower those are trasmitted to a switching station for landlines, but I suppose some companies my use a switching station for each sector.

You mean how is interference from nearby cellsites avoided?

Firstly, the signal received by the mobile from the "other" cellsite is going to be NdB below the signal from the "desired" tower regardless of whether they're both transmitting at 3W or both at 30W. Generally speaking, it's the relative strength of the two signals that matters.

Secondly, remember that the mobile has a pretty crappy receive antenna. Even if the cellsite is transmitting 10 times the power as the mobile, the signal seen by the mobiles recevier's front end may not be any stronger than the signal seen by the cellsite receiver's front end.

If a cellsite receive antenna has 10dB of gain compared to the mobile's receiver antenna, then the cellsite _has_ to transmit

10X as much power in order for both receivers to see the same signal levels.

Likewise, if the cellsite receiver can be built to tolerate 3dB worse S/N ratio, the mobile can cut it's tx power in half and you still have the same bandwitdh/quality in both directions.

It depends. There's usually only a single switch for a large group of cells. The links between the switch and the cells can be copper, fiber, or microwave.

Most people around here are used to flying in crappy weather. It's that or no flying for 8 months of the year!

Sure! And I've flown in 30mph winds with no problems. But would I launch something like that big multi K Buff in something like that? Even though I can afford to pay for and lose a dozen like that, no way would I risk it in those conditions.

Try as I might, for the life of me, I just can't see how having cellophane near your transmitter can cause interference.

Oh - nevermind!

Ed Cregger

snipped-for-privacy@webtv.net (Bill Sheppard) wrote in news: snipped-for-privacy@storefull-3173.bay.webtv.net:

Ouch. For the rest of us, $5k x 8 = $40k. That's an expensive Figure-9. I don't know if they'll allow another 8 engines.

Yes, that was a little eerie, both sharing same attitude and fate.

Almost then sounds like some non-scale changes to conventional ailerons for stability would have of course, detracted a little from scale for the purist, but for most observers, still fly reasonably like the real thing (with out the nasty tendencies.)

"Chuck Jones" wrote in news:7i4ne.26055$iU.15021@lakeread05:

I was going on memory, but after reviewing that video again, they announced it, although "Wren" didn't come out too clearly. Even with sponsored engines, that was an expensive crash. Any model airplane that costs more than a good motorcycle is not worth owning! ;-)

So far the only inteference I am sure of is from the charger for my cell phone. It puts out garbage on the car radio when charging. I suppose one could bring a cell phone near an AM portable radio and listen for the various pulse noise being radiated. For example a TV remote puts out a lot of hash that can be heard on the AM band when the remote is near the receiver. Transmitters are susceptable to picking up inteference and rebroadcasting it but the inteferring signal would probably have to be strong.

What I am trying to say is those conditions weren't all that bad. Looked a lot worse on camera than the actual.

Ed, it doesn't cause interference. There is anectotal evidence that something in the design of the two items allows the cell phone to alter programming in the receiver.

Top posting is annoying enough, but when you put the quoted material below your sig it makes it especially hard to fix (intelligent newsreaders that trim sigs when quoting postings).

Just as sarcasm and hyperbole are often taken literally, Emily Latella imitations are often missed. To make it more obvious, always start an Emily Latella bit with "What's all this about ?". IIRC, the ending was usually "Oh. Well that's different. Nevermind."

Oh, and remember to type in a high, nasal voice.

I forgot about the prelude. Thanks, Grant.

Ed Cregger