PPRuNe Forums - Emirates vs 5G US

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Quote:

Originally Posted by 3db (Post 11173327)

andrasz
Even more interesting, this was in the mid 1990’s but before Dec 1999. As part of the monthly calibration check of our navigation kit (typical aircraft commercial kit, albeit one receiver was modified for flight inspection use by the manufacturer) after calibration and everything back together with all covers on, I could reliably get my cellphone (cant remember brand/model) to move the glideslope full scale in both directions by walking up and down the workshop. The Nav kit was all on the bench, driven by appropriate sig generators (no aerials in circuit), all very well earthed. Never tried it airborne. If I remember correctly, there was an area of little or no interference within about 1-2m of the kit. However, as soon as I moved further away down the workshop the glideslope (and only the glideslops) would give false readings. The phone was not making/receiving a call, but was communication on data channels with the cellphone base station. I remember I switched my phone off, problem disappeared, hence the source was my phone, and not the cell base station. Glideslope is 330-335MHz and G1 cellphones 890-960MHz, hence 3rd harmonic interference was a likely source. Aircraft kit is built to a spec, but cellphone was built to a price, maybe the transmitter was out of spec? BTW, the workshop was at Biggin Hill, UK.

You just brought it to the point - the price tag on the phone says a bit about the precession of the technology and back in the 90’s the spec where properly not sufficient not to disturb other systems, especially in that close proximity, and therefore back than it was a good advice to switch of phones while on board of an aeroplane. And an ILS is by its analog design highly volatile to disturbance.
i remember back than :
1994 something like d-net (800/900mhz analog signal modulation)
from 1995 on or so E- net or better known as GSM started take place (significantly smaller phones (800/900mhz carrier first digital modulations) transmitter density increased as power output of phones shrinked and first data applications came up.

digital signals are a rectangular signal form and therefore they are the sum of a endless number of sin waves in every third harmonic - says a low cost filter design leaves a wide spread frequency spectrum passing left and right of a carrier which spreads than into neighboring channels or even other frequency bands causing eventually disturbance there.

the way out of this is proper testing, limiting frequency bands allowed around critical areas, and enough margins between telecom and aviation frequencies. The catch here is that per definition the band of 4.2 to 4.4 GHz is part of the 5G network plan and quite essential in the current 5G rollout given the current amount of mobile used data

The price point is always the major consideration in domestic kit. This can introduce major design compromises, mainly based on probability. You are right proper testing is the way forward, but who pays for it? The advice for g1 cellphones was turn them off on aircraft, the third harmonic for an ILS had not been investigated (at least by the cellular companies, don’t know about aviation/CAA). No marketing took place for cellphone in the aviation sector – I think everyone wanted more real world experience in everyday situations before suggesting situations that could be life or death. The size of the kit was not helpful for general personal use either, the first “pocket-able” mobiles arrived in early 1985. However at 20x8x4cm with a 15cm rubber enclosed aerial, it was a bit of a stretch to say you could put it in your pocket.

It was mid 1992 if I recall, that vodaphone introduced GSM in the UK, with other operators following a year or two later. We then started to get large reductions in kit size, but still with good performance. Never tested a GSM in the workshop, so I don’t know how it performed against an ILS on the bench. As you say, they clearly have the potential to be more disruptive to an ILS, but maybe filter design had improved? Also, power output is more accurately controlled now, mainly to extend battery life.

I was employed in aviation from May 1997 to about June/July 1999, so whilst a GSM phone was available, my luddite approach didn’t allow me to get one. I never like the thought I could be tracked via the phone (found that out in 1985) so kept my mobile to the oldest standard that still worked. At least you could turn them off and remove the battery in those days! Nothing to hide by the way, just if you want to track me do it overtly, not covertly.