ILS G/S

[Tony Gover]

I'm having trouble getting a Narco Nav 122D working. Help please!!
I have had the instrument checked by a Radio shop here in France and it checks OK on the bench. I then flew the aircraft to the Radio shop and it checked OK with a hand held transmitter in front of the wing with or without the engine running.
BUT!! When I fly to my local ILS airfield, the VOR and Localiser are fine(the antenna is up on the fin) but the glide slope gives a fly up signal below slope, on glide slope signal on slope, BUT a fly up signal when I go above slope. I have built 4 different antennas and tried them on the fin (that interfered with the VHF antenna just below it), under the fuselage,
under the cocpit roof and 3/4 of the way out in the left wing. Always the same fly up signal above slope.

Narco have never heard of this problem, the radio technician says the instrument is fine and the installation too. Try another airfield but Avignon is a commercial airport used by jets and there is nothing wrong with their ILS. Has anyone got any ideas. My VOR/LOC, VHF and transponder antennas work fine.

Sorry but I don't know if Avignon is a two, three, or three+ Antena system. It is gobbledegook to me. I start my run at 2,000 ft (usually) about 7 nm out but always well below the glide slope beam and I go through the glide slope at a constant height. For bad weather reasons the ILS is on 17 (comes from the med') but 95% of the time runway 35 is the active. I cause little disruption to other traffic if I keep the height constant and above circuit height. But I have not yet seen a fly down signal. Below slope fly up, reducing to on slope, then fly up again when above slope. The engine is a VW Porsche mix, no magnetos (CDI car type ignition. The engine rpm gauge is powered an electic pulse from the engine, but it is via a coax cable. That does not affect the VHF radio, transponder or Dynon EFIS so I have no reason to suspect that and changing engine rpm doesn't change anything.

Thanks for the two replies so far. More ideas welcome.

Thanks Tony Gover

[bertdeleporte]

HI,

on your home airport, is the GS is a two, a three or three + control antennas system?

Could you be tracking a false lobe of the GS?

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False signals may be generated along the glide slope in multiples of the glide path angle, the first being approximately 6º degrees above horizontal. This false signal will be a reciprocal signal (i.e. the fly up and fly down commands will be reversed). The false signal at 9º will be oriented in the same manner as the true glide slope. There are no false signals below the actual slope. An aircraft flying according to the published approach procedure on a front course ILS should not encounter these false signals

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http://www.allstar.fiu.edu/aero/ILS.htm

Bertrand