David Lesher wrote:
> B J Foster
yahoo.com> writes:
> >>> I've actually seen mobile phones interfere with VOR, the needle
>>> swinging from side to side until they are turned off.
>
>> I find this very hard to believe.
>
>> The VOR band is 108MHz to 118Mhz (VHF). The lowest mobile band (UHF) is
>> 900Mhz. If the VOR system has such a poor filter then it is going to be
>> affected by *every* *other* system between VOR and GSM.
>
> You don't seem to understand RF very well. Lots of weird things happen,
> when you mix multiple emitters and Murphy.
Sure. Such as?
>
> First of all, GSM phones emit subcarriers, specifically the harmonics
> of its switching speed. They tends to get into LOTS of things such as
> hospital telemetry.
Harmonics are at higher frequencies, e.g. 800Mhz GSM has harmonics at
(say) 3x = 2.4GHz. Now this might interfere with 802.11 but it is even
*less* likely to interfere with VHF.
Now VHF harmonics might interfere with GSM, but the problem isn't the
"safety of the cellphone" is it?
>
> Second, the front end of a the VOR is 100 Mhz; but the IF's are often
> poorly shielded; put an emitter near by them and....
...what?
The NASA/Oklahoma tests covered several different types of aircraft, one
had a non-metal frame and that had the lowest path loss (as you'd
expect). It was still negligible. e.g. -30db basically mean that 1/1000
of the power emitted by the PED survives the path to the VOR antenna -
and then it is filtered - and if the filter is so bad that 800MHz gets
through then every other frequency between 118MHz and 800MHz will *also*
get through.
>
> Years back, a friend was in a FAA test aircraft, ISTM it was the old
> 727 they had, and while testing a new Mode-S transponder, all was
> well...until they came in to land, the gear cycled and the GPWS went off
> when the radar altimeter went bonkers. It had been tested BUT oops when
> the gear doors were open in transit, it reflected enough RF back that...
What were the frequencies of the altimeter and the transponder? TCAS?
>
> There's another gotchas out there in aviation, like O2 bottles.
> Let's not add move variables.
There is a lot of *attention* given to safety, so consequently it is
*much* safer to travel by air than any other means.
