My 320 header tank fuel information system
Consists of a capacitive fuel probe and the related gauge (w/needle)
From Sky Sports.
Wing tanks are equipped with VMI probes,(automatic)  transfer to header and
to engine.

1st problem
Since the first flight (sep 2003) I always had the fuel level indicator
Which was dropping from an indicated "exact" value to the "Empty"
information, when transmitting over my KX165 or the GNC 420.

During the last years I could live with this (not state of the art) fact...

2nd problem
Recently the header tank information began indicating unstable (lower)
Fuel quantities. This additional problem was isolated and with a certain
Probability to the (dual) electronic ignition.
Ground tests confirmed this, when RMP > 1700 instability of indication
rises.


Then I decided to investigate to the first problem:

€ Stabilized (w/Regulator to 12.1V) the Fuel probes and gauges power Supply
   -> still the same problem

€ applied different shielding (of the output signal ) options between Fuel
Probe and Gauge.
   -> still the same problem

€ Operating the System from a 9V Battery.
   -> improvement, still minor instability.

Result was at 118 MHz little variation and at 136 MHz the "big one"...
[At least there a certain correlation could be confirmed]

Analyzed (with Klaus 's great and appreciated help) he second problem.
No error source could be located at the ignition system.

All the other Systems HSI, Autopilot DME, Glide slope etc. works perfect..
The VSWR of the two antennas seems to be OK. (not measured now)


Does anyone have a suggestion? Should I change to the fuel level sensor
The the "Princeton Capacitive Fuel probes", as VMI are not any longer
An option...


Thank you for any helpful information


Patrick Hayoz
LNC2, HB-YHQ