[time-nuts] GPS from a window seat

Robert Atkinson robert8rpi at yahoo.co.uk
Sun Oct 4 09:14:29 UTC 2009

This is correct. There was also an issue with harmonics from the local oscillator in the aircraft's own VHF nav/comm receivers blocking the GPS. The answer is a 1575MHz notch filter, e.g. http://www.edmo.com/index.php?module=products&func=display&prod_id=18006
Another problem was bias oscillators in tape players, these could interfere with Omega/VLF receivers. Not a problem now of course. While on the subject of Omega/VLF If you come across a Global GNS-500A OEU box, it has a Efratom FRK Rb in it. There is one on ebay at the moment, item 150257671674, but the price is way to high.
It's very had to predict interference on aircraft. While the probability is low the consequences during take-off and landing are severe. Hence the total ban on electronics during these flight phases. The "illegality" is endangering an aircraft, however you do it. Avionics design is my day job.
Robert G8RPI MRAeS 

--- On Sun, 4/10/09, David I. Emery <die at dieconsulting.com> wrote:

From: David I. Emery <die at dieconsulting.com>
Subject: Re: [time-nuts] GPS from a window seat
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Date: Sunday, 4 October, 2009, 8:36 AM

On Sun, Oct 04, 2009 at 12:20:26AM -0700, Hal Murray wrote:
> > Why the ban on AM/FM receivers? 
> I assume it's EMI from the local oscillator.
> Is anybody shipping an AM/FM radio that isn't superhet?

    FWIW, I have read and been told that there was an era when some
cheap AM/FM radios put out a lot of signal from the LO 10.7 MHz away
from FM stations and that at least a few of them used high side LOs
which would put that LO signal potentially right in the middle of the
band used by VOR navigation beacons and ILS localizers... just above the
FM band from 108-118 MHz.   This would obviously not be good if the
signal power was great enough to interfere with navigation receivers.

    The broad rule was put in place because there was no effective
way of determining if any particular radio a passenger might have
radiated or if it even had FM tuning capability.  It was safer just to
ban everything because of those few radios that were way outside of
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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