FireMedic_2009
Well Known Member
A friend of mine has a Lancair 290 and has GNC355. He first noticed a problem when his xcruse AP would lose coupling and show a gps flag while doing practice approaches. His plane has been grounded for 1.5 yrs due to needing cracked cylinders replaced which was completed 6 months ago. The GPS and AP was installed about 2.5 yrs ago but only flies VFR and mainly uses the AP for enroute navigation so he was not aware of the GPS flag shown on the AP prior to the cylinders being replaced. He is a retired military and airline pilot and is wanting to become current again for IFR in case he needs to get into or out of an airport that has morning IFR conditions in the winter months. Below is info he posted on the Lancair forum:
Still having problems with this. I replaced the short antenna cable the installer put in with a 6 1/2 foot antenna cable as recommended by Garman. It takes 2 to 3 minutes after the gps is powered up, but I end up getting 9 to 11 satellites. However any time I key the mic to transmit on a frequency between 120.0 and 122.0, satellite reception as displayed immediately drops to zero. The satellite display goes completely blank, then takes a few seconds to recover. I have a Bendix KX 155 and PS Industries PAR 100 (Garmin says the KX155 does not have filters for part number with a -22 and below. My KX155 has a -42 at the end of the part number). It does this when I transmit from either one of these radios only on a frequency from 120.0 to 122.0. I bought a notch filter and experimented with it attached to each antenna cable right next to the radio in turn. No change with either. I talked with Garmin. He said it could be interference with your ELT where the Com transmission could excite the circuit on the ELT even though the ELT is not ON or triggered. Garmin told me to remove the ELT and put it in your trunk of my car to shield it away from Com transmission while I was troubleshooting on the ground. I did that and the gps drops off when transmitting on these frequencies. He said it could be reflection between the metal hangars. I taxied to a large open space on the ramp away from the hangars and it did the same thing. I powered down each radio in turn with its antenna disconnected to isolate the other radio. It did the same thing. These were all ground tests this afternoon. I’m baffled. Key the mic on any of those frequencies, and the satellites are instantly gone. On frequencies 122.1 - 122.7 the gps drops off but it takes 3-5 seconds to loose all the satellites in the gps. Obviously this is not good if one were on a coupled RNAV approach and used the radio. The antenna is on a ground plane of about 10” x 14” of which the Garmin was made aware of which the tech did not see that as a problem.
Is anyone familiar with this type of problem and know of a solution?
Still having problems with this. I replaced the short antenna cable the installer put in with a 6 1/2 foot antenna cable as recommended by Garman. It takes 2 to 3 minutes after the gps is powered up, but I end up getting 9 to 11 satellites. However any time I key the mic to transmit on a frequency between 120.0 and 122.0, satellite reception as displayed immediately drops to zero. The satellite display goes completely blank, then takes a few seconds to recover. I have a Bendix KX 155 and PS Industries PAR 100 (Garmin says the KX155 does not have filters for part number with a -22 and below. My KX155 has a -42 at the end of the part number). It does this when I transmit from either one of these radios only on a frequency from 120.0 to 122.0. I bought a notch filter and experimented with it attached to each antenna cable right next to the radio in turn. No change with either. I talked with Garmin. He said it could be interference with your ELT where the Com transmission could excite the circuit on the ELT even though the ELT is not ON or triggered. Garmin told me to remove the ELT and put it in your trunk of my car to shield it away from Com transmission while I was troubleshooting on the ground. I did that and the gps drops off when transmitting on these frequencies. He said it could be reflection between the metal hangars. I taxied to a large open space on the ramp away from the hangars and it did the same thing. I powered down each radio in turn with its antenna disconnected to isolate the other radio. It did the same thing. These were all ground tests this afternoon. I’m baffled. Key the mic on any of those frequencies, and the satellites are instantly gone. On frequencies 122.1 - 122.7 the gps drops off but it takes 3-5 seconds to loose all the satellites in the gps. Obviously this is not good if one were on a coupled RNAV approach and used the radio. The antenna is on a ground plane of about 10” x 14” of which the Garmin was made aware of which the tech did not see that as a problem.
Is anyone familiar with this type of problem and know of a solution?
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