Nav/Comm Radios Can Blank Out GPS
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If you're here looking for the reason cell phones are banned on airline flights, look elsewhere. This site relates to interference with "suction cup" receivers in aircraft, in which the antenna is attached to the window in the manner of a radar detector. It is impossible for a cell phone to interferes with avionics installed in an aircraft.
The following link addresses Cell Phones and Personal Electronics on
Airlines.
ANOTHER NOTE
this website is NOT directed to the EOW cycle! The EOW Cycle
and Loss of Almanac Bugs are described at the bottom of this page.
This primarily affects handheld GPS with antennas inside the aircraft. It is caused by the IF local oscillator (LO) used in superheterodyne receivers. The problem occurs when the nav/com is in the receive mode. That is blatantly obvious to EE's but counter-intuitive to others. If the radio is turned off, it will not transmit the LO signal. The standby frequency does not cause problems.
The signal primarily leaks from the faceplate although it could theoretically leak from the back or through the sides.
The worst offenders seem to be the Narco digitals, although this
artificial "selective availability" has been reported in
King digitals and King 170's.
*** The NAV frequency of 115.50 is the default NAV frequency, which comes up every time you turn on the radio. So select two nav stations on preflight like you're supposed to!
Narco Mk12/D/E & Nav 824/825 if not wired with memory keep-alive or upgraded to Plus configuration will default to 115.5 in the active channel and will jam any GPS receiver while on this frequency.
I called Narco and the person who identified himself as the
customer service manager stated that Narco does not keep a list of
frequencies, and that the frequencies vary between individual
radios. He stated that I was the first person who ever asked for
a list of these frequencies! I asked for a recommended fix, and he
stated that they have nothing but I could place a piece of metal
over the faceplate. (This on an 810 and an 825!)
Instead of following Narco's advise and sticking a piece of metal over the faceplate, it should be possible to do one of two things:
I tried the aluminum tape but it didn't have a significant effect on the problem. I didn't measure reception strength but the radios still blank the GPS. Obviously I couldn't find this particular repair in the shop manuals.
If you do this, use strips long enough to wrap around the inside of the faceplate. This will:
I suspect my cellphone may be causing problems. It's a CDMA unit and doesn't cause a visible loss of signal levels. The nature of the CDMA control channel may nevertheless cause interference.
Just put the phone in the back seat when not using it, or turn it off.
Garwin and presumably other GPS units will seem to forget how to find satellites if not used for several weeks. This is corrected by a reset procedure found on the manufacturer's website. At least on Garmin, the reset does not erase the database or user waypoints.
If let standing for considerable time with no battery or a completely dead battery, the internal battery on the unit will also fail. That repair normally takes someone equipped with an appropriate weapon (solder gun). Send it back to the factory for refurbishment; they'll also update the software.
21-Aug-99 is the "EWO" date. This is a 20 year end-of-cycle date for the GPS almanac, sometimes referred to as the Y2K bug of GPS. Most Garwin units need their clocks erased either with a patch or by manually erasing most data. This is described at their website. AFAIK, most GPS units are able to function past the EOW cycle, but without the EOW "patch" will malfunction during 4 weeks starting with the EOW date.
To reset a Garmin GPS - If it goes "brain dead", for example after shipping the GPS:
Once the disk is used, Garmin databases will not work on a second GPS unit. Therefore update your database from a copy of the original disk. This applies if the license is for one computer only; if it says "for one GPS unit only" then I guess you're not supposed to update more than one GPS, even with the same computer. Why can't I find this database on Napster?
