FreeFlight 2101 I/O PLUS, Руководство по установке и проверке

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Page 3-15
Revision E
May 31, 2006
FreeFlight 2101 I/O Approach Plus GPS Navigation System
3.2.4.3 Comm Test
Harmonic interference from VHF transmissions on the following frequencies may affect GPS signal reception:
Frequency in MHz
121.150 131.250
121.175 131.275
121.200 131.300
Installations intended for IFR approvals should be tested to ensure no interference is generated by VHF
transmissions.
For each interfering frequency, perform the following test:
1. Tune the VHF radio to the frequency under test.
2. While observing the GPS satellites tracked display and internal GPS annunciator, key the VHF transmitter
for 20 seconds.
3. If the number of satellites in use drops to the point that GPS navigation is no longer possible, then too much
interference exists between VHF radio and the FreeFlight 2101 I/O Approach Plus.
Two common sources of interference are from the VHF radio front panel to the GPS antenna and from the
VHF antenna to the GPS antenna.
To minimize front panel to antenna interference, ensure that all cabin doors and windows are closed when
performing the test. This type of interference is also minimized by being away from the ground and ground
structures. If required, the test may be performed in flight. Finally, the location of the GPS antenna may
affect levels of VHF front panel to GPS antenna interference.
For VHF antenna to GPS antenna interference, a filter may be inserted in line with the VHF transmission
line.
The following filters are recommended:
VENDOR VENDOR P/N
FSY MICROWAVE, INC. LC539-7BBM
1055 First Street
Rockville, MD 20850
PH: (301) 294-8950
FAX: (301) 294-3007
TRILITHIC 3LC500-3-50-CD
9202 East 33rd Street
Indianapolis, IN 46236
PH: (800) 344-2412
FAX: (317) 895-3613
SPECIFICATIONS FOR LOW PASS FILTER
I.L. = 0.4 dB max. @ 140 MHz
3 dB cutoff = 539 MHz nominal
50 dBc @ 1500 MHz
Power: 30 Watts CW
Size: 0.5" Dia. X 3.00" T.T.
Connectors: BNC female/ male
After modifying installation as appropriate, repeat steps 1 and 2 for each interfering frequency. If interference
continues, please contact FreeFlight Technical Support at (254) 662-0000.